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The role of the genetic elements blaoxa and IS Aba 1 in the Acinetobacter calcoaceticus-Acinetobacter baumannii complex in carbapenem resistance in the hospital setting

Abstract:

INTRODUCTION:

Members of the Acinetobacter genus are key pathogens that cause healthcare-associated infections, and they tend to spread and develop new antibiotic resistance mechanisms. Oxacillinases are primarily responsible for resistance to carbapenem antibiotics. Higher rates of carbapenem hydrolysis might be ascribed to insertion sequences, such as the ISAba1 sequence, near bla OXA genes. The present study examined the occurrence of the genetic elements bla OXA and ISAba1 and their relationship with susceptibility to carbapenems in clinical isolates of the Acinetobacter calcoaceticus-Acinetobacter baumannii complex.

METHODS:

Isolates identified over 6 consecutive years in a general hospital in Joinville, Southern Brazil, were evaluated. The investigation of 5 families of genes encoding oxacillinases and the ISAba1 sequence location relative to bla OXA genes was conducted using polymerase chain reaction.

RESULTS:

All isolates presented the bla OXA-51-like gene (n = 78), and 91% tested positive for the bla OXA-23-like gene (n = 71). The presence of ISAba1 was exclusively detected in isolates carrying the bla OXA-23-like gene. All isolates in which ISAba1 was found upstream of the bla OXA-23-like gene (n = 69) showed resistance to carbapenems, whereas the only isolate in which ISAba1 was not located near the bla OXA-23-like gene was susceptible to carbapenems. The ISAba1 sequence position of another bla OXA-23-like-positive isolate was inconclusive. The isolates exclusively carrying the bla OXA-51-like gene (n = 7) showed susceptibility to carbapenems.

CONCLUSIONS:

The presence of the ISAba1 sequence upstream of the bla OXA-23-like gene was strongly associated with carbapenem resistance in isolates of the A. calcoaceticus-A. baumannii complex in the hospital center studied.

Keywords:
Acinetobacter calcoaceticus-Acinetobacter baumannii complex; bla OXA ; ISAba1; Carbapenem antibiotics

INTRODUCTION

Healthcare-associated infections (HAI) are increasingly affecting public and private healthcare systems and raising not only hospital costs but also the morbidity and mortality rates of affected patients11. Lin L, Nonejuie P, Munguia J, Hollands A, Olson J, Dam Q, et al. Azithromycin synergizes with cationic antimicrobial peptides to exert bactericidal and therapeutic activity against highly multidrug-resistant Gram-negative bacterial pathogens. EBioMedicine 2015; 2:690-698.) (22. Kuo SC, Lee YT, Lauderdale TLY, Huang WC, Chuang MF, Chen CP, et al. Contribution of Acinetobacter-derived cephalosporinase-30 to sulbactam resistance in Acinetobacter baumannii. Front Microbiol 2015; 6:1-9.) (33. Freire ILS, Menezes LCC, Sousa NML, Araújo RO, Vasconcelos QLDAQ, Torres GV. Epidemiologia das infecções relacionadas à assistência à saúde em Unidade de Terapia Intensiva Pediátrica. Rev Bras Cienc Saude 2013; 11:9-15.. The bacterial genus Acinetobacter is recognized as a key HAI-causing pathogen that is associated with high mortality rates in hospital settings22. Kuo SC, Lee YT, Lauderdale TLY, Huang WC, Chuang MF, Chen CP, et al. Contribution of Acinetobacter-derived cephalosporinase-30 to sulbactam resistance in Acinetobacter baumannii. Front Microbiol 2015; 6:1-9.) (44. Pagano M, Martins AF, Machado AB, Barin J, Barth AL. Carbapenem-susceptible Acinetobacter baumannii carrying the ISAba1 upstream bla OXA-51-like gene in Porto Alegre, southern Brazil. Epidemiol Infect 2012; 141:330-333.. Acinetobacter has considerable capacity to spread and develop new antibiotic resistance mechanisms55. Chen TL, Lee Y, Kuo SC, Hsueh PR, Chang FY, Siu LK, et al. Emergence and distribution of plasmids bearing the bla OXA-51-like gene with an upstream ISAba1 in carbapenem-resistant Acinetobacter baumannii isolates in Taiwan. Antimicrob Agents Chemother 2010; 11:4575-4581.. Consequently, numerous HAI outbreaks caused by multidrug-resistant (MDR) representatives of the Acinetobacter calcoaceticus-Acinetobacter baumannii complex have been reported in several countries, including Brazil22. Kuo SC, Lee YT, Lauderdale TLY, Huang WC, Chuang MF, Chen CP, et al. Contribution of Acinetobacter-derived cephalosporinase-30 to sulbactam resistance in Acinetobacter baumannii. Front Microbiol 2015; 6:1-9.) (55. Chen TL, Lee Y, Kuo SC, Hsueh PR, Chang FY, Siu LK, et al. Emergence and distribution of plasmids bearing the bla OXA-51-like gene with an upstream ISAba1 in carbapenem-resistant Acinetobacter baumannii isolates in Taiwan. Antimicrob Agents Chemother 2010; 11:4575-4581.) (66. Tognim MC, Andrade SS, Silbert S, Gales AC, Jones RN, Sader HS. Resistance trends of Acinetobacter spp. in Latin America and characterization of international dissemination of multi-drug resistant strains: five-year report of the SENTRY Antimicrobial Surveillance Program. International J Infect Dis 2004; 8:284-291..

Oxacillinase-type (OXA) carbapenemases (Ambler class D β-lactamases) are the primary factors responsible for resistance to carbapenem antibiotics worldwide77. Kusradze Ia, Diene SM, Goderdzishvili M, Rolain JM. Molecular detection of OXA carbapenemase genes in multidrug-resistant Acinetobacter baumannii isolates from Iraq and Georgia. Int J Antimicrob Agents 2011; 38:164-168.) (88. Opazo A, Domínguez M, Bello H, Amyes SG, Rocha GG. OXA-type carbapenemases in Acinetobacter baumannii in South America. J Infect Dev Ctries 2012; 6:311-316.. Approximately 150 variants have already been described, and at least 45 show carbapenem-hydrolyzing activity77. Kusradze Ia, Diene SM, Goderdzishvili M, Rolain JM. Molecular detection of OXA carbapenemase genes in multidrug-resistant Acinetobacter baumannii isolates from Iraq and Georgia. Int J Antimicrob Agents 2011; 38:164-168.. OXAs are genetically divided into 6 subgroups. The most commonly identified examples are bla OXA-23-like (OXA-23, OXA-27, and OXA-49), bla OXA-24-like (OXA-24, OXA-25, OXA-26, OXA-40, and OXA-72), bla OXA-58-like, bla OXA-143-like (OXA-143, OXA-231, and OXA-253), bla OXA-235, and bla OXA-51-like. The latter subgroup is intrinsic to A. baumannii species88. Opazo A, Domínguez M, Bello H, Amyes SG, Rocha GG. OXA-type carbapenemases in Acinetobacter baumannii in South America. J Infect Dev Ctries 2012; 6:311-316.) (99. Higgins PG, Pérez FJL, Zander E, Fernández A, Bou G, Seifert H. OXA-235, a novel class D β-lactamase involved in resistance to carbapenems in Acinetobacter baumannii. Antimicrob Agents Chemother 2013; 57:2121-2126.. Higher carbapenem hydrolysis rates have been reported to result from the acquisition of insertion sequences (ISs) that affect the expression of the bla OXA genes encoding oxacillinases1010. Peleg AY, Seifert H, Paterson DL. Acinetobacter baumannii: emergence of a successful pathogen. Clin Microbiol Rev 2008; 21:538-582.) (1111. Nowak P, Paluchowska P, Budak A. Distribution of bla OXA genes among carbapenem-resistant Acinetobacter baumannii nosocomial strains in Poland. New Microbiol 2012; 35:317-325.) (1212. Segal H, Garny S, Elisha BG. Is ISAba1 customized for Acinetobacter? FEMS Microbiol Lett 2005; 243:425-429.) (1313. Turton JF, Woodford N, Glover J, Yarde S, Kaufmann ME, Pitt TL. Identification of Acinetobacter baumannii by detection of the bla OXA-51-like carbapenemase gene intrinsic to this species. J Clin Microbiol 2006; 44:2974-2976.) (1414. Mugnier PD, Poirel L, Nordmann P. Functional analysis of insertion sequence ISAba1, responsible for genomic plasticity of Acinetobacter baumannii. J Bacteriol 2009; 191:2414-2418.. These elements are the smallest and most abundant transposable elements and are capable of causing mutations and rearrangements in the genome, thereby contributing to the spread of resistance and virulence determinants in various bacterial species1515. Martinez P, Mattar S. Imipenem-resistant Acinetobacter baumannii carrying the ISAba1-bla OXA-23, bla OXA-51 and ISAba1-bla adc-7 genes in Monteria, Colombia. Braz J Microbiol 2012; 43:1274-1280..

Different ISs have been described in the A. calcoaceticus-A. baumannii complex in association with specific genes; these sequences play a key role in the development of carbapenem resistance1515. Martinez P, Mattar S. Imipenem-resistant Acinetobacter baumannii carrying the ISAba1-bla OXA-23, bla OXA-51 and ISAba1-bla adc-7 genes in Monteria, Colombia. Braz J Microbiol 2012; 43:1274-1280.. Insertion sequence Acinetobacter baumannii 1 (ISAba1) belongs to the IS4 family and has been identified in association with several antibiotic resistance genes in the A. calcoaceticus-A. baumannii complex1414. Mugnier PD, Poirel L, Nordmann P. Functional analysis of insertion sequence ISAba1, responsible for genomic plasticity of Acinetobacter baumannii. J Bacteriol 2009; 191:2414-2418.) (1515. Martinez P, Mattar S. Imipenem-resistant Acinetobacter baumannii carrying the ISAba1-bla OXA-23, bla OXA-51 and ISAba1-bla adc-7 genes in Monteria, Colombia. Braz J Microbiol 2012; 43:1274-1280.. The role of ISAba1 in increasing gene expression was demonstrated for the bla ampC gene encoding cephalosporinase and the bla OXA-23-like genes encoding an OXA that hydrolyzes carbapenems1515. Martinez P, Mattar S. Imipenem-resistant Acinetobacter baumannii carrying the ISAba1-bla OXA-23, bla OXA-51 and ISAba1-bla adc-7 genes in Monteria, Colombia. Braz J Microbiol 2012; 43:1274-1280.. Some studies have also linked the presence of the ISAba1 sequence upstream of the bla OXA-51-like gene to carbapenem resistance phenotypes44. Pagano M, Martins AF, Machado AB, Barin J, Barth AL. Carbapenem-susceptible Acinetobacter baumannii carrying the ISAba1 upstream bla OXA-51-like gene in Porto Alegre, southern Brazil. Epidemiol Infect 2012; 141:330-333.) (1515. Martinez P, Mattar S. Imipenem-resistant Acinetobacter baumannii carrying the ISAba1-bla OXA-23, bla OXA-51 and ISAba1-bla adc-7 genes in Monteria, Colombia. Braz J Microbiol 2012; 43:1274-1280..

The diversity of the genetic elements involved in the resistance of the A. calcoaceticus-A. baumannii complex to antibiotics has spurred research on these determinants of resistance11. Lin L, Nonejuie P, Munguia J, Hollands A, Olson J, Dam Q, et al. Azithromycin synergizes with cationic antimicrobial peptides to exert bactericidal and therapeutic activity against highly multidrug-resistant Gram-negative bacterial pathogens. EBioMedicine 2015; 2:690-698.) (22. Kuo SC, Lee YT, Lauderdale TLY, Huang WC, Chuang MF, Chen CP, et al. Contribution of Acinetobacter-derived cephalosporinase-30 to sulbactam resistance in Acinetobacter baumannii. Front Microbiol 2015; 6:1-9.) (44. Pagano M, Martins AF, Machado AB, Barin J, Barth AL. Carbapenem-susceptible Acinetobacter baumannii carrying the ISAba1 upstream bla OXA-51-like gene in Porto Alegre, southern Brazil. Epidemiol Infect 2012; 141:330-333.) (1616. Castilho SRA. Caracterização fenotípica e molecular de Acinetobacter baumannii isolados de pacientes de UTIs de Goiânia, com relação à capacidade de formar biofilmes e resistência aos carbapenêmicos. Master's dissertation. Goiânia: Universidade Federal de Goiás; 2013. 97 p.) (1717. Carramachi IN, Carvalho KR, Cruz JGV, Zahner V. A preliminary molecular epidemiologic study using analysis of variable number of tandem repeats of Acinetobacter baumannii OXA-23 producing strains isolated from hospitals in Rio de Janeiro State, Brazil. Rev Pan-Amaz Saude 2014, 5:57-62.) (1818. Salimizand H, Noori N, Meshkat Z, Ghazvini K, Amel SJ. Prevalence of Acinetobacter baumannii harboring ISAba1/bla OXA-23-like family in a burn center. Burns 2015; 41:1100-1106.) (1919. Bahador A, Raoofian R, Farshadzadeh Z, Beitollahi L, Khaledi A, Rahimi S, et al. The prevalence of ISAba1 and ISAba4 in Acinetobacter baumannii species of different international clone lineages among patients with burning in Tehran, Iran. Jundishapur J Microb 2015; 8:1-9.. On the basis of the findings of these studies, the present study examined the occurrence of the genetic elements bla OXA and ISAba1 in clinical isolates belonging to the A. calcoaceticus-A. baumannii complex and their association with phenotypic susceptibility to carbapenem antibiotics.

METHODS

Selection of clinical isolates and ethical aspects

The study was conducted at Dona Helena Hospital, a private general hospital with 189 beds, and at the Molecular Biology Laboratory of the University of Region of Joinville [Universidade da Região de Joinville (UNIVILLE)], both located in Joinville, Santa Catarina, Brazil. Clinical isolates belonging to the A. calcoaceticus-A. baumannii complex identified over 6 consecutive years, starting in March 2009, were included in the study. Isolates related to HAI (healthcare-associated infection after 48h of admission), colonization (presence of the microorganism without clinical signs of related infection), and surveillance culture upon admission (detection of colonization in patients referred from other healthcare institutions at the time of hospital admission) according to the criteria defined by the Hospital Infection Control Service of the hospital center studied were included in the study. Only the first isolate obtained from patients with 2 or more isolates derived from the same anatomical site during the same period of hospitalization was considered for this study. All isolates were identified by the Microscan Walkaway automated system (Siemens, Munich, Germany) complemented by Gram staining.

This study was evaluated and approved by the Research Ethics Committee of UNIVILLE (Opinion 788.455).

Antibiotic susceptibility analysis

The determination of the antibiotic susceptibility profile was performed using the disc-agar diffusion method (Kirby and Bauer)2020. Bauer AW, Kirby WM, Sherris JC, Turck M. Antibiotic susceptibility testing by a standardized single disk method. J Clin Pathol 1966; 45:493-496.. The inhibition halos were interpreted according to the current recommendations of the Clinical and Laboratory Standards Institute (CLSI)2121. Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing: 20th Informational Supplement. Published 2010. http://www.clsi.org/
http://www.clsi.org/...
for each corresponding year.

Imipenem and meropenem discs with 10μg of each antibiotic were used. Simultaneously, other classes of antibiotics were tested in the following amounts indicated by the CLSI: amikacin (30μg), ampicillin/sulbactam (10/10μg), ceftazidime (30μg), ciprofloxacin (5μg), doxycycline (30μg), gentamicin (10μg), piperacillin/tazobactam (100/10μg), polymyxin B (300 units), sulfamethoxazole/trimethoprim (1.25/23.75μg), and tobramycin (10μg). All discs were from the same manufacturer (Oxoid, Cambridge, UK).

Bacterial DNA preparation and evaluation

The heat shock method was used to prepare bacterial deoxyribonucleic acid (DNA) from a pure culture grown in MacConkey agar2222. Vaneechoutte M, Dijkshoorn L, Tjernberg I, Elaichouni A, de Vos P, Claeys G, et al. Identification of Acinetobacter genomic species by amplified ribossomal DNA restriction analysis. J Clin Microbiol 1995; 33:11-15.. Initially, 3 colonies collected using a bacteriological loop were resuspended in 100μL of ultrapure sterile water (Milli-Q, São Paulo, Brazil). The suspension was subjected to a boiling water bath for 5 min and then cold shocked in an ice bath for 5 min. The boiling and cooling procedures were repeated, followed by centrifugation at 8,000 ×g for 10 min. The supernatant containing the bacterial DNA was evaluated through spectrophotometric readings at 260 and 280nm and then stored at -20°C.

The extracted bacterial DNA was assessed by polymerase chain reaction (PCR) to determine its viability for use in the subsequent genotypic analyses. A pair of primers specific to the A. calcoaceticus-A. baumannii complex [gltA-F (5′-AATTTACAGTGGCACATTAGGTCC-3′) and gltA-R (5′-GCAGAGATACCAGCAGAGATACACG-3′)] was used to amplify a single 722-bp fragment of the gltA gene encoding bacterial citrate synthase2323. Bartual SG, Seifert H, Hippler C, Luzon MA, Wisplinghoff H, Rodríguez-Valera F. Development of a multilocus sequence typing scheme for characterization of clinical isolates of Acinetobacter baumannii. J Clin Microbiol 2005; 43:4382-4390.. The thermocycling conditions were as follows: initial denaturation at 94°C for 3 min; 30 cycles of 94°C for 1 min, 62°C for 30 s, and 72°C for 1 min; and final extension at 72°C for 10 min2323. Bartual SG, Seifert H, Hippler C, Luzon MA, Wisplinghoff H, Rodríguez-Valera F. Development of a multilocus sequence typing scheme for characterization of clinical isolates of Acinetobacter baumannii. J Clin Microbiol 2005; 43:4382-4390..

Investigation of the genetic elements associated with oxacillinase production

The occurrence of the bla OXA-23-like, bla OXA-24-like, bla OXA-51-like, bla OXA-58-like, and bla OXA-143-like genes in the selected isolates was investigated using multiplex PCR with the primers outlined in Table 1(2424. Woodford N, Ellington MJ, Coelho JM, Turon JF, Ward ME, Brown S, et al. Multiplex PCR for genes encoding prevalent OXA carbapenemases in Acinetobacter spp Int J Antimicrob Agents 2006; 27:351-353.) (2525. Higgins PG, Lehmann M, Seifert H. Inclusion of OXA-143 primers in a multiplex polymerase chain reaction (PCR) for genes encoding prevalent OXA carbapenemases in Acinetobacter spp. Int J Antimicrob Agents 2010; 35:305.. The reactions were conducted in a final volume of 50μL containing approximately 50-500ng of extracted DNA and a reagent mixture with 1U Platinum(r) Taq DNA polymerase (Invitrogen, São Paulo, Brazil), 200μM dNTPs mix (GE Healthcare, Little Chalfont, United Kingdom), 1× PCR buffer (Invitrogen), 20 pmol of each primer (DNA Express, São Paulo, Brazil), and 1.5mM of MgCl2 (Invitrogen). The reactions were performed in an XP Cycler device (BIOER Technology, Tokyo, Japan) at the following conditions: initial denaturation at 94°C for 3 min; 30 cycles of 1 min at 94°C, 30s at 52°C, and 1 min at 72°C; and final extension at 72°C for 10 min2424. Woodford N, Ellington MJ, Coelho JM, Turon JF, Ward ME, Brown S, et al. Multiplex PCR for genes encoding prevalent OXA carbapenemases in Acinetobacter spp Int J Antimicrob Agents 2006; 27:351-353..

The presence of the ISAba1 promoter sequence in the isolates and its association with the bla OXA-23-like and bla OXA-51-like genes were investigated by PCR1212. Segal H, Garny S, Elisha BG. Is ISAba1 customized for Acinetobacter? FEMS Microbiol Lett 2005; 243:425-429.) (2626. Antonio CS, Neves PR, Medeiros M, Mamizuka EM, Elmor de Araújo MR, Lincopan N. High prevalence of carbapenem-resistant Acinetobacter baumannii carrying the bla OXA-143 gene in brazilian hospitals. Antimicrob Agents Chemother 2011; 55:1322-1323.) (2727. Turton JF, Ward ME, Woodford N, Kaufmann ME, Pike R, Livermore DM, et al. The role of ISAba1 in expression of OXA carbapenemase genes in Acinetobacter baumannii. FEMS Microbiol Lett 2006; 258:72-77.. The primer sequences and the sizes of the expected reaction products are outlined in Table 1. Excluding the primers (10 pmol of each primer per reaction), all other components were used in quantities identical to those described for the multiplex PCR, and the reactions were performed using the same thermocycler. The initial denaturation was performed at 94°C for 3 minutes, followed by 30 cycles of denaturation at 94°C for 1 min, hybridization at 50°C for 1 min, and extension at 72°C for 2 min. The final extension was performed at 72ºC for 5 min.

TABLE 1
Primers used to detect genes encoding oxacillinases and ISAba1.

The PCR products were subjected to submerged electrophoresis (TBE buffer, 10 V/cm) in a 1% agarose gel with 0.5µg/mL ethidium bromide. The expected fragments were confirmed by exposure to ultraviolet light (300nm) in a transilluminator (MiniBis-Pro Photodocumentation System - DNR Bio-Image Systems Ltd., Jerusalem, Israel), followed by scanning.

Standard strains of the A. calcoaceticus-A. baumannii complex from the collection of cultures of the Oswaldo Cruz Foundation [Fundação Oswaldo Cruz (FIOCRUZ), Rio de Janeiro, Brazil] labeled 7892 (bla OXA-24-like), 7740 (bla OXA-58-like), and 7572 (bla OXA-23-like and bla OXA-143-like) were used as positive controls. The carbapenem-susceptible A. calcoaceticus-A. baumannii American Type Culture Collection (ATCC) strain 19606 was used as the negative control.

Data analysis

A database was created using Excel 2013 (Microsoft Corp., Redmond, WA, USA) for phenotypic and genotypic data collection and analysis. Appropriate percentages were calculated, and data were analyzed descriptively.

RESULTS

Seventy-eight clinical isolates belonging to the A. calcoaceticus-A. baumannii complex derived from 60 patients (12 individuals contributed 2 or more isolates) were employed in the phenotypic and genotypic analyses established for the study. All isolates were positive for amplification of the bla OXA-51-like gene fragment. These isolates were identified in clinical samples from patients with HAI (66.7%), surveillance culture upon admission (15.4%), and colonization (17.9%).

The isolates were collected from bronchoalveolar lavage (38.5%), wound secretions (12.8%), rectal swabs (12.8%), blood (9%), urine (6.4%), and other types of samples (20.5%). The distribution of isolates by hospital department showed that 53.8% were derived from the intensive care unit (ICU); 29.5%, from the inpatient units; 10.3%, from the emergency room; and 6.4%, from the surgical center. The temporal evolution in relation to the sectors and types of samples corresponding to the analyzed isolates is shown in Table 2.

TABLE 2
Distribution of clinical isolates according to sample type and hospital department over 6 years (2009-2015).

Phenotypic analysis

Evaluation of antibiotic susceptibility profiles showed that 88.5% (n = 69) of the isolates were resistant to the carbapenems imipenem and meropenem (Figure 1). Simultaneously, the proportions of resistance to the other antibiotics tested were distributed as follows: ciprofloxacin, 88.3% (68/77); piperacillin/tazobactam, 87.2% (68/78); sulfamethoxazole/trimethoprim, 74.3% (52/70); ceftazidime, 68.4% (52/76); ampicillin/sulbactam, 41% (32/78); amikacin, 41% (32/78); tobramycin, 28.4% (21/74); doxycycline, 13.7% (10/73), and gentamicin, 10.8% (8/74). All isolates exhibited full susceptibility to polymyxin B.

FIGURE 1
In vitro antibiotic susceptibility profile of Acinetobacter calcoaceticus-Acinetobacter baumannii clinical isolates (%): R: resistant; I: intermediate and S: susceptible.

Genotypic evaluation

All extracted DNA samples enabled the amplification of the gltA gene segment and were considered viable for subsequent genotypic analyses. Figure 2 depicts the electrophoretic pattern resulting from the PCR analysis of the main subgroups of genes encoding oxacillinases and ISAba1 in the clinical isolates of the present study.

FIGURE 2
Identification of genetic elements associated with the production of oxacillinases by PCR. M: molecular marker (100bp; Fermentas, Ontario, Canada); 1: bla OXA-51-like (353bp); 2: bla OXA-51-like (353bp) and bla OXA-23-like (501bp); 3: ISAba1 (548bp) and 4: ISAba1 + bla OXA-23-like (875bp). PCR: polymerase chain reaction.

Seventy-one of the isolates phenotypically identified as belonging to the A. calcoaceticus-A. baumannii complex had the genes bla OXA-23-like and bla OXA-51-like, whereas 7 exclusively amplified bla OXA-51-like. The genes bla OXA-24-like, bla OXA-58-like, and bla OXA-143-like were not detected.

All isolates carrying the bla OXA-23-like gene (n = 71) also had the ISAba1 promoter sequence; this sequence was located upstream from the bla OXA-23-like gene in 69 isolates. A single isolate carried ISAba1, which was not associated with the location of bla OXA-23-like, whereas another isolate proved inconclusive in terms of the insertion position. The ISAba1 sequence was not observed upstream of the bla OXA-51-like gene in the analyzed isolates.

Evaluation of the association between genetic markers and phenotypic resistance to carbapenems

All isolates with ISAba1 located upstream of the bla OXA-23-like gene (n = 69) showed resistance to imipenem and meropenem and were identified during the 6 consecutive years of observation (93.7%, 91.7%, 100%, 91.7%, 85%, and 72.7% of the resistant isolates in each year). Conversely, the only isolate in which ISAba1 was not coupled to bla OXA-23-like was susceptible to carbapenems and was identified in year 1. The isolates exclusively containing bla OXA-51-like (n = 7; 1 in year 2, 1 in year 4, 2 in year 5, and 3 in year 6) also showed full susceptibility to imipenem and meropenem.

DISCUSSION

Carbapenems are the antibiotics of choice for the treatment of infections caused by β-lactam-resistant bacteria of the A. calcoaceticus-A. baumannii complex. However, resistance to carbapenems has increased, thereby limiting the use of this class of antibiotics1515. Martinez P, Mattar S. Imipenem-resistant Acinetobacter baumannii carrying the ISAba1-bla OXA-23, bla OXA-51 and ISAba1-bla adc-7 genes in Monteria, Colombia. Braz J Microbiol 2012; 43:1274-1280.. The present study demonstrated that the presence of the ISAba1 promoter sequence associated with the bla OXA-23-like gene in A. calcoaceticus-A. baumannii was strongly associated with resistance to carbapenem antibiotics in the hospital setting.

The species A. baumannii is the most important and representative member of the A. calcoaceticus-A baumannii complex, and it is considered the leading pathogen of the Acinetobacter genus in health institutions worldwide1010. Peleg AY, Seifert H, Paterson DL. Acinetobacter baumannii: emergence of a successful pathogen. Clin Microbiol Rev 2008; 21:538-582.. Small genomic differences exist among the species of this genus and have been reported by several authors; however, A. calcoaceticus, A. baumannii, A. pittii, and A. nosocomialis are closely related and are collectively termed the A. calcoaceticus-A. baumannii complex owing to the difficulty in separating them using conventional tests1616. Castilho SRA. Caracterização fenotípica e molecular de Acinetobacter baumannii isolados de pacientes de UTIs de Goiânia, com relação à capacidade de formar biofilmes e resistência aos carbapenêmicos. Master's dissertation. Goiânia: Universidade Federal de Goiás; 2013. 97 p.) (2828. Bérézin EB, Towner KJ. Acinetobacter spp. as nosocomial pathogens: microbiological, clinical, and epidemiological features. Clin Microbiol Rev 1996; 9:148-165.. A. baumannii species identification may be confirmed by detecting the presence of the bla OXA-51 gene because it naturally occurs in the A. baumannii chromosome2929. Brown S, Amyes S. OXA (beta)-lactamases in Acinetobacter: the story so far. J Antimicrob Chemother 2006; 57:1-3.) (3030. Feizabadi MM, Fathollahzadeh B, Taherikalani M, Rasoolinejad M, Sadeghifard N, Aligholi M, et al. Antimicrobial susceptibility patterns and distribution of bla OXA genes among Acinetobacter spp. isolated from patients at Tehran hospitals. J Infect Dis 2008; 61:274-278.. This gene is intrinsic to the species and has been identified in a wide collection of isolates of the A. calcoaceticus-A. baumannii complex collected from various geographic areas1313. Turton JF, Woodford N, Glover J, Yarde S, Kaufmann ME, Pitt TL. Identification of Acinetobacter baumannii by detection of the bla OXA-51-like carbapenemase gene intrinsic to this species. J Clin Microbiol 2006; 44:2974-2976.) (2828. Bérézin EB, Towner KJ. Acinetobacter spp. as nosocomial pathogens: microbiological, clinical, and epidemiological features. Clin Microbiol Rev 1996; 9:148-165.) (2929. Brown S, Amyes S. OXA (beta)-lactamases in Acinetobacter: the story so far. J Antimicrob Chemother 2006; 57:1-3.) (3131. Aly M, Tayeb HT, Al Johani SM, Alyamani EJ, Aldughaishem F, Alabdulkarim I, et al. Genetic diversity of bla OXA-51-like genes among multidrug-resistant Acinetobacter baumannii in Riyadh, Saudi Arabia. Eur J Clin Microbiol Infect Dis 2014; 33:1223-1228.) (3232. Levin AS, Mendes CM, Sinto SI, Sader HS, Scarpitta CR, Rodrigues E, et al. An outbreak of multiresistant Acinetobacter baumannii in a university hospital in São Paulo, Brazil. Infect Control Hosp Epidemiol 1996; 17:366-368.. Thus, phenotypically identified isolates that possess the bla OXA-51-like gene were considered members of the complex in the present study. Conversely, recent studies have reported the plasmid-encoded carbapenemase OXA-51 in clinical isolates of Acinetobacter nosocomialis and in other genospecies not corresponding to A. baumannii1717. Carramachi IN, Carvalho KR, Cruz JGV, Zahner V. A preliminary molecular epidemiologic study using analysis of variable number of tandem repeats of Acinetobacter baumannii OXA-23 producing strains isolated from hospitals in Rio de Janeiro State, Brazil. Rev Pan-Amaz Saude 2014, 5:57-62.) (3333. Lee MH, Chen TL, Lee YT, Huang L, Kuo SC, Yu KW, et al. Dissemination of multidrug-resistant Acinetobacter baumannii carrying bla OXA-23 from hospitals in central Taiwan. J Microbiol Immunol Infect 2013; 46:419-424.) (3434. Pinheiro RR, Sabagh BP, Vidal LMR, Veras JFC, Vieira VV, Souto ASS, et al. Avaliação da contaminação microbiana em produtos desinfetantes de uso geral. Rev Inst Adolfo Lutz 2013; 72:170-174.) (3535. Teixeira AB, Martins AF, Barin J, Hermes DM, Pitt CP, Barth AL. First report of carbapenem-resistant Acinetobacter nosocomialis isolates harboring ISAba1-bla OXA-23 genes in Latin America. J Clin Microbiol 2013; 51:2739-2741..

Acinetobacter baumannii has become particularly problematic due to its increased prevalence and resistance to carbapenem antibiotics3636. Chagas TP, Carvalho KR, de Oliveira Santos IC, Carvalho-Assef AP, Asensi MD. Characterization of carbapenem-resistant Acinetobacter baumannii in Brazil (2008-2011): countrywide spread of OXA-23-producing clones (CC15 and CC79). Diagn Microbiol Infect Dis 2014; 79:468-472.. In the present study, 88.5% (69/78) of the isolates showed resistance to carbapenems. According to the Antimicrobial Surveillance Program in Latin America, the resistance rates of Acinetobacter spp. to carbapenems increased from 6.4%, 12.6%, and 0% between 1997 and 1999 to 84.9%, 71.4%, and 50.0% between 2008 and 2010 in Argentina, Brazil, and Chile, respectively3636. Chagas TP, Carvalho KR, de Oliveira Santos IC, Carvalho-Assef AP, Asensi MD. Characterization of carbapenem-resistant Acinetobacter baumannii in Brazil (2008-2011): countrywide spread of OXA-23-producing clones (CC15 and CC79). Diagn Microbiol Infect Dis 2014; 79:468-472.) (3737. Quiñones D, Carvajal I, Perez Y, Hart M, Perez J, Garcia S, et al. High prevalence of bla OXA-23 in Acinetobacter spp. and detection of bla NDM-1 in A. soli in Cuba: report from National Surveillance Program (2010-2012). New Microbes New Infect 2015; 7:52-56.. A cohort study conducted in 5 ICUs of tertiary hospitals of the metropolitan area of the City of Goiânia, Goiás, Brazil, showed a high rate of A. baumannii resistance to carbapenems (73.4%), which is higher than the mean values reported by other Brazilian institutions (25-45%)3838. Godoy CSM. Infecções por Acinetobacter baumannii em adultos admitidos em unidades de terapia intensiva (UTIs) de Goiânia e Aparecida de Goiânia Goiânia (GO). Master's dissertation. Goiânia: Universidade Federal de Goiás; 2012. 86 p..

Oxacillinase production corresponding to bla OXA-23-like expression is the most common carbapenem resistance mechanism in A. calcoaceticus-A. baumannii reported in various countries, including Bulgaria, China, Iraq, Afghanistan, France, and Polynesia3939. Mugnier PD, Poirel L, Naas T, Nordmann P. Worldwide dissemination of the bla OXA -23 carbapenemase gene of Acinetobacter baumannii. Emerg Infect Dis2010; 16:35-40.. In the present study, 91% (71/78) of the isolates were positive for bla OXA-23-like amplification. A study conducted by Carvalho et al.1717. Carramachi IN, Carvalho KR, Cruz JGV, Zahner V. A preliminary molecular epidemiologic study using analysis of variable number of tandem repeats of Acinetobacter baumannii OXA-23 producing strains isolated from hospitals in Rio de Janeiro State, Brazil. Rev Pan-Amaz Saude 2014, 5:57-62. in 10 public and private hospitals in the City of Rio de Janeiro from 2005 to 2007 showed similar results, with the detection of bla OXA-23-like in 96% of the isolates. This rate is higher than the rates observed in studies conducted in other countries, both nationwide, such as in Taiwan (21.1%), or restricted to a few local hospitals, such as in Romania (84.6%), Tunisia (82%), Greece (72.4%), and Italy (40%)3333. Lee MH, Chen TL, Lee YT, Huang L, Kuo SC, Yu KW, et al. Dissemination of multidrug-resistant Acinetobacter baumannii carrying bla OXA-23 from hospitals in central Taiwan. J Microbiol Immunol Infect 2013; 46:419-424..

The expression of bla OXA genes might be increased by the presence of the ISAba1 sequence upstream of the enzyme-encoding gene, which provides higher levels of resistance to carbapenems1414. Mugnier PD, Poirel L, Nordmann P. Functional analysis of insertion sequence ISAba1, responsible for genomic plasticity of Acinetobacter baumannii. J Bacteriol 2009; 191:2414-2418.. The presence of ISAba1 was detected in all isolates positive for bla OXA-23-like gene amplification in the present study (n = 71). Furthermore, all isolates wherein ISAba1 was located upstream of the bla OXA gene (n = 69) showed resistance to carbapenems. This profile of a strong association between ISAba1 and bla OXA-23-like was repeated during the 6 years of observation, which suggests the occurrence of cross-infection, dissemination, and long-term permanence of this resistance mechanism in the hospital center studied. The only isolate wherein ISAba1 was not located upstream of the bla OXA-23-like gene showed susceptibility to carbapenems. Thus, the presence of bla OXA-23-like without the ISAba1 promoter sequence might not be sufficient to cause carbapenem hydrolysis, as reported by Carvalho et al.4040. Carvalho KR, Assef APDC, Santos LG, Pereira MJF, Asensi MD. Occurrence of bla OXA-23 gene in imipenem-susceptible Acinetobacter baumanniiMem Inst Oswaldo Cruz 2011; 106:505-506. OXA-51 carbapenemases encoded by intrinsic (chromosomal) genes have a weak capacity to hydrolyze carbapenems1111. Nowak P, Paluchowska P, Budak A. Distribution of bla OXA genes among carbapenem-resistant Acinetobacter baumannii nosocomial strains in Poland. New Microbiol 2012; 35:317-325.) (4141. Figueiredo DA, Vianna RPT, Nascimento JA. Epidemiologia da infecção hospitalar em uma Unidade de Terapia Intensiva de um hospital público municipal de João Pessoa-PB. Rev Bras de Cien Saude 2013; 17:233-240.. The presence of ISAba1 may provide a strong promoter for the bla OXA-51-like gene, thereby increasing its expression and causing resistance4242. Barin J, Martins AF, Heineck BL, Barth AL, Zavascki AP. Hetero and adaptive resistance to polymyxin B in OXA-23-producing carbapenem-resistant Acinetobacter baumannii isolates. Ann Clin Microbiol Antimicrob 2013; 12:15.) (4343. Figueiredo S, Poirel L, Croize J, Recule C, Nordmann P. In vivo selection of reduced susceptibility to carbapenems in Acinetobacter baumannii related to ISAba1-mediated overexpression of the natural bla OXA-66 oxacillinase gene. Antimicrob. Agents Chemother 2009; 53:2657-2659.) (4444. Ruiz M, Marti S, Fernandez-Cuenca F, Pascual A, Vila J. Prevalence of ISAba1 in epidemiologically unrelated Acinetobacter baumannii clinical isolates. FEMS Microbiol Lett 2007; 274:63-66.. A study conducted in the United Kingdom by Turton et al.2727. Turton JF, Ward ME, Woodford N, Kaufmann ME, Pike R, Livermore DM, et al. The role of ISAba1 in expression of OXA carbapenemase genes in Acinetobacter baumannii. FEMS Microbiol Lett 2006; 258:72-77. showed that carbapenem hydrolysis by isolates carrying the bla OXA-51-like gene only occurred in bacteria in which ISAba1 was upstream of the gene, suggesting that this IS acted as a promoter for the expression of this gene. Antonio et al.2626. Antonio CS, Neves PR, Medeiros M, Mamizuka EM, Elmor de Araújo MR, Lincopan N. High prevalence of carbapenem-resistant Acinetobacter baumannii carrying the bla OXA-143 gene in brazilian hospitals. Antimicrob Agents Chemother 2011; 55:1322-1323. reported that, in their study performed in hospitals of the Southeast and South regions of Brazil from 2004 to 2008, ISAba1 was not observed upstream of the bla OXA-51-like gene; furthermore, none of the isolates analyzed showed the carbapenem-resistant phenotype. The results in our study were similar because only 9% (7/78) of the isolates exclusively amplified bla OXA-51-like, and none amplified ISAba1 concomitantly; moreover, all these isolates were susceptible to carbapenems. This finding reinforces the hypothesis that the absence of ISAba1 or its presence in a region not upstream of the bla OXA-51-like gene renders a very low or nonexistent ability to hydrolyze carbapenems in A. baumannii isolates without other bla OXA genes.

The emergence of carbapenem resistance has limited the treatment of HAIs caused by A. baumannii3636. Chagas TP, Carvalho KR, de Oliveira Santos IC, Carvalho-Assef AP, Asensi MD. Characterization of carbapenem-resistant Acinetobacter baumannii in Brazil (2008-2011): countrywide spread of OXA-23-producing clones (CC15 and CC79). Diagn Microbiol Infect Dis 2014; 79:468-472.) (3838. Godoy CSM. Infecções por Acinetobacter baumannii em adultos admitidos em unidades de terapia intensiva (UTIs) de Goiânia e Aparecida de Goiânia Goiânia (GO). Master's dissertation. Goiânia: Universidade Federal de Goiás; 2012. 86 p.. In the present study, 41% of the isolates showed resistance to ampicillin/sulbactam, which is nearly half that of the 85.2% rate reported by Carvalho et al.4545. Carvalho MR, Moreira ICCC, Amorin Neta FL, Guimarães MSO, Viana VGF, Oliveira FW. Incidência de bactérias multirresistentes em uma unidade de terapia intensiva. R Interd 2015; 8:75-85. from 2002 to 2010 in the ICU of a public institution in the City of Teresina, Piauí, Brazil. The use of ampicillin/sulbactam has been effective for the treatment of systemic infections caused by MDR A. baumannii; however, a steady decline in susceptibility rates has been reported in recent decades4646. Lin MF, Lan CY. Antimicrobial resistance in Acinetobacter baumannii: From bench to bedside. World J Clin Cases 2014; 2:787-814.) (4747. Viehman JA, Nguyen MH, Doi Y. Treatment options for carbapenems resistant and extensively drug-resistant Acinetobacter baumannii infections. Drugs 2014; 74:1315-1333.. Furthermore, in Latin America, A. baumannii has been commonly reported as being MDR, with high rates of resistance to other antibiotics in addition to carbapenems, including ceftazidime, piperacillin/tazobactam, and ciprofloxacin. Thus, Latin America appears to be the highest-ranking region in the world for the prevalence of MDR A. baumannii3838. Godoy CSM. Infecções por Acinetobacter baumannii em adultos admitidos em unidades de terapia intensiva (UTIs) de Goiânia e Aparecida de Goiânia Goiânia (GO). Master's dissertation. Goiânia: Universidade Federal de Goiás; 2012. 86 p.. In a study conducted using 155 A. baumannii isolates from 11 Brazilian states from 2008 to 2011, Chagas et al.3636. Chagas TP, Carvalho KR, de Oliveira Santos IC, Carvalho-Assef AP, Asensi MD. Characterization of carbapenem-resistant Acinetobacter baumannii in Brazil (2008-2011): countrywide spread of OXA-23-producing clones (CC15 and CC79). Diagn Microbiol Infect Dis 2014; 79:468-472.) demonstrated that most isolates also showed resistance to more than 5 classes of antibiotics in addition to carbapenems. The highest rates were observed for ciprofloxacin, cefepime, and piperacillin/tazobactam, with 99.4% resistant isolates, followed by ceftazidime (97.4%), sulfamethoxazole/trimethoprim (23.9%), and amikacin (11.6%); however, the isolates did display susceptibility to polymyxin B. In the present study, 88.3%, 87.2%, and 68.4% of the isolates showed resistance to ciprofloxacin, piperacillin/tazobactam, and ceftazidime, respectively, and all analyzed isolates were susceptible to polymyxin B. However, higher rates of resistance were observed for sulfamethoxazole/trimethoprim (74.5%) and amikacin (41%). These data suggest that the use of polymyxins should be highlighted as a therapeutic option for HAIs caused by A. baumannii4848. Fishbain J, Peleg AY. Treatment of Acinetobacter infections. Clin Infect Dis 2010; 51:79-84.. Polymyxin B and colistin have long been used as antibiotic agents, but they cause nephrotoxicity and neurotoxicity. Nevertheless, they are considered effective in treating infections caused by carbapenem-resistant A. baumannii4949. Gales AC, Reis AO, Jones RN. Contemporary assessment of antimicrobial susceptibility testing methods for polymyxin B and colistin: review of available interpretative criteria and quality control guidelines. J Clin Microbiol 2001; 39:183-190.. Unfortunately, resistance to these antibiotics is also emerging3636. Chagas TP, Carvalho KR, de Oliveira Santos IC, Carvalho-Assef AP, Asensi MD. Characterization of carbapenem-resistant Acinetobacter baumannii in Brazil (2008-2011): countrywide spread of OXA-23-producing clones (CC15 and CC79). Diagn Microbiol Infect Dis 2014; 79:468-472.) (5050. Falagas ME, Koletsi PK, Bliziots IA. The diversity of definitions of multidrug-resistant (MDR) and pandrug-resistant (PDR) Acinetobacter baumannii and Pseudomonas aeruginosa. Int J Med Microbiol 2006; 55:1619-1629..

Acinetobacter baumannii also stands out because it is an opportunistic pathogen in HAI episodes, especially in ICUs3434. Pinheiro RR, Sabagh BP, Vidal LMR, Veras JFC, Vieira VV, Souto ASS, et al. Avaliação da contaminação microbiana em produtos desinfetantes de uso geral. Rev Inst Adolfo Lutz 2013; 72:170-174.. In particular, invasive mechanical ventilation - a life support method widely used in ICUs - is usually associated with nosocomial infection by A. baumannii5151. Nepomuceno RM, Silva LD. Pesquisa bibliográfica dos sistemas de vigilância em ventilação mecânica: o estado da arte na enfermagem. Rev Eletron Enfermagem 2007; 9:191-199.. In a study performed using 500 isolates from 30 hospitals of 10 Cuban provinces from 2010 to 2012, Quiñones et al.3737. Quiñones D, Carvajal I, Perez Y, Hart M, Perez J, Garcia S, et al. High prevalence of bla OXA-23 in Acinetobacter spp. and detection of bla NDM-1 in A. soli in Cuba: report from National Surveillance Program (2010-2012). New Microbes New Infect 2015; 7:52-56. demonstrated that the hospital unit with the highest number of cases of A. calcoaceticus-A. baumannii infection was the ICU (60.2%) and that the respiratory tract had the highest rate of positive cultures (38.6%). Godoy et al.3838. Godoy CSM. Infecções por Acinetobacter baumannii em adultos admitidos em unidades de terapia intensiva (UTIs) de Goiânia e Aparecida de Goiânia Goiânia (GO). Master's dissertation. Goiânia: Universidade Federal de Goiás; 2012. 86 p.) showed that the lungs were also the most common site of infection with A. baumannii among patients monitored in 5 ICUs of Goiânia (53.1% of cases). Similar results were observed in our study, in which 53.8% (42/78) of the isolates were derived from the ICU, and the majority of positive cultures were derived from bronchoalveolar lavage (66.7%; 28/42).

Acinetobacter calcoaceticus-A. baumannii colonization should be analyzed because it may precede cases of infection and contribute to the endemicity of this agent in healthcare institutions, in addition to being a key microorganism related to HAIs5252. Silva RNP. A Importância do Acinetobacter baumannii na infecção adquirida nos cuidados de saúde. Master's dissertation. Porto: Universidade de Porto; 2009. 21p.. In the present study, 17.9% (14/78) of the isolates were related to patient colonization, a prevalence higher than the 9.4% A. baumannii colonization rate reported by Godoy et al.3838. Godoy CSM. Infecções por Acinetobacter baumannii em adultos admitidos em unidades de terapia intensiva (UTIs) de Goiânia e Aparecida de Goiânia Goiânia (GO). Master's dissertation. Goiânia: Universidade Federal de Goiás; 2012. 86 p.. Surveillance cultures of patients transferred from other institutions were adopted in the hospital studied during year 3. A total of 12 cases positive for A. baumannii were confirmed, including 7 in year 5 (6 isolates from rectal swabs and 1 from wound secretion) and 5 in the following year (4 isolates derived from rectal swabs and 1 from tissue fragments). All the cases were identified within 48h of admission.

Our study had some limitations. First, the number of isolates was relatively small despite the period of 6 years covered by the analyses, and the study was performed at a single hospital center. Second, the included patients had several comorbidities, and some underwent multiple hospital admissions, which complicated the evaluation of the impact on the numbers related to colonization. Therefore, we recommend conducting similar multicenter studies involving a greater number of hospitals and evaluating the clinical and epidemiological characteristics associated with HAIs and the risk factors. Furthermore, we propose an investigation of the association between genetic profiles related to resistance and the severity and clinical outcomes of the affected patients using standardized clinical scores. Finally, we consider it pertinent to conduct the genotyping of isolates identified in the hospital to examine the clonal relationship between resident strains and possible community-acquired strains, thereby highlighting possible flaws in infection control.

In conclusion, this study provides data on the prevalence of isolates belonging to the A. calcoaceticus-A. baumannii complex carrying genetic elements associated with carbapenem resistance. The emergence and spread of variants of the bla OXA gene encoding carbapenemases and of ISs capable of increasing bla OXA expression in A. baumannii in Brazil underscore the need for the medical community and health managers to remain alert to the potential threat of outbreaks of carbapenem-resistant isolates, especially those with the ISAba1 sequence upstream of the bla OXA-23-like gene.

Acknowledgments

The authors would like to thank the Molecular Biology Laboratory of Universidade da Região de Joinville (UNIVILLE) and Dona Helena Hospital.

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  • This study was supported by a research fund from the University of Region of Joinville [Fundo de Apoio à Pesquisa (FAP)/UNIVILLE].

Publication Dates

  • Publication in this collection
    Jul-Aug 2016

History

  • Received
    14 Mar 2016
  • Accepted
    12 July 2016
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