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Detection and molecular characterization of β-lactamase genes in clinical isolates of Gram-negative bacteria in Southern Ecuador

ABSTRACT

This work performed a phenotypic and genotypic characterization of 79 clinical isolates of Enterobacteriaceae and Pseudomonadaceae collected in hospitals of Southern Ecuadorin 2013. Our results showed a high incidence of β-lactamases and ESBLs with blaTEM and blaCTX-M as the prevalent genes, respectively. By direct sequencing of PCR amplicons, the different β-lactamases and variants of the genes were also distinguished. Our results revealed a predominance of TEM-1 β-lactamase and the presence of different CTX-M variants with a prevalence of CTX-M-15. Two infrequent CTX-M variants in South America were also identified. To the best of our knowledge, this is one of the first studies describing the genetic characteristics of β-lactamases in Ecuador.

Keywords:
β-Lactam resistance; β-Lactamase; ESBL; Genotypic characterization

Since the discovery of antibiotics, many pathogens which had been considered defeated have continued to develop resistance to these drugs. The emergence of resistant microorganisms to antibiotics is a problem that has extended globally.11 Jansen WT, van der Bruggen JT, Verhoef J, Fluit AC. Bacterial resistance: a sensitive issue complexity of the challenge and containment strategy in Europe. Drug Resist Updat. 2006;9:123-33.,22 Magiorakos AP, Srinivasan A, Carey RB, et al. Multidrug-resistant, extensively drug-resistant and pandrug-resistant bacteria: an international expert proposal for interim standard definitions for acquired resistance. Clin Microbiol Infect. 2012;18:268-81. This phenomenon is widespread in hospitals mainly because of the large and often inappropriate use of antimicrobials. However, due to the bacteria's ability to exchange genetic information, environmental and nosocomial pathogens have developed the same resistance mechanisms, since most resistance genes have their probable origin in environmental microorganisms.33 Dantas G, Sommer MO, Oluwasegun RD, Church GM. Bacteria subsisting on antibiotics. Science. 2008;320:100-103. Resistant pathogens to most antibiotics have already been described, but in particular it is of great impact the resistance to β-lactams. Resistance to these antimicrobial agents is due to the production of β-lactamases, and the genes encoding these enzymes have been found worldwide mainly in Gram-negative bacteria, prevalently in Enterobacteriaceae and Pseudomonas spp.44 Paterson DL, Bonomo RA. Extended-spectrum beta-lactamases: a clinical update. Clin Microbiol Rev. 2005;18:657-86.,55 Bradford PA. Extended-spectrum beta-lactamases in the 21st century: characterization, epidemiology, and detection of this important resistance threat. Clin Microbiol Rev. 2001;14:933-51.

Among β-lactamases, extended-spectrum β-lactamases (ESBLs), AmpC-type β-lactamases, and carbapenemases are of great concern. In particular ESBLs are the most abundant in Enterobacteriaceae, with more than 600 natural variants (http://www.lahey.org/Studies/), and with a prevalence of CTX-M family that became predominant over TEM and SHV during the first decade of the 21st century.66 Canton R. Epidemiology and evolution of beta-lactamases. In: Baquero FNC, Cassell G, Gutiérrez-Fuentes J, editors. Evolutionary biology of bacterial and fungal pathogens. Washington: ASM Press; 2008. p. 249–70.

As far as we know, there is a lack of detailed reports characterizing the β-lactamase spread in Ecuador.77 Jones RN, Guzman-Blanco M, Gales AC, et al. Susceptibility rates in Latin American nations: report from a regional resistance surveillance program (2011). Braz J Infect Dis. 2013;17:672-81.,88 Bonelli RR, Moreira BM, Picao RC. Antimicrobial resistance among Enterobacteriaceae in South America: history, current dissemination status and associated socioeconomic factors. Drug Resist Updat. 2014;17:24-36. In this work a phenotypic and molecular characterization of β-lactamases was performed in clinical pathogens isolated in two main public hospitals of the Loja province, Ecuador.

The clinical isolates of Enterobacteriaceae and Pseudomonas aeruginosa were obtained from patients of Ygnacio Monteros and IESS Hospitals. The samples were collected between May and November 2013, while the bacterial cultures were grown in agar-MacConkey Petri dishes, identified by traditional biochemical testing and validated by Microgen™ GnA + B-ID system.

Antimicrobial susceptibility testing was performed by Kirby-Bauer disk diffusion procedure according to CLSI guidelines.99 CLSI. Performance standards for antimicrobial susceptibility testing. 22nd informational supplement. CLSI document M100-S22. Wayne, PA: Clinical and Laboratory Standards Institute; 2012. The isolates were tested for susceptibility to amikacin (AMK), amoxicillin/clavulanic acid (AMC), ampicillin (AMP), ampicillin/sulbactam (SAM), aztreonam (ATM), cefepime (FEP), cefotaxime (CTX), cefoxitin (FOX), ceftazidime (CAZ), ciprofloxacin (CIP), imipenem (IMP), meropenem (MEM), netilmicin (NET), and piperacillin/tazobactam (PTZ). The investigation of phenotypic production of ESBL and AmpC-type β-lactamase was performed by techniques of double disk synergism (DDST) on Mueller Hinton agar and combination disk method. In particular for ESBL detection, DDST was performed on agar with AMC-20/10 µg disk positioned 25 mm (center-to-center) away from disks containing CAZ-30 µg, CTX-30 µg, FEP-30 µg and ATM-30 µg, and the confirmation combination disk method with disks of CTX-30 µg, cefotaxime/clavulanic acid (30/10 µg), CAZ-30 µg and ceftazidime/clavulanic acid (30/10 µg)1010 Drieux L, Brossier F, Sougakoff W, Jarlier V. Phenotypic detection of extended-spectrum beta-lactamase production in Enterobacteriaceae: review and bench guide. Clin Microbiol Infect. 2008;14(Suppl. 1):90-103.; for AmpC-type β-lactamase detection, DDST (for constitutive AmpC) was performed with boronic acid containing disk (30 µg) placed at a center-to-center distance to a CAZ-30 µg and a CTX-30 µg disk of 25 mm, while for combination disk method (for inducible AmpC), disks of CTX-30 µg, CAZ-30 µg and ATM-30 µg were placed close to a IMP-10 µg.1111 Yagi T, Wachino J, Kurokawa H, et al. Practical methods using boronic acid compounds for identification of class C beta-lactamase-producing Klebsiella pneumoniae and Escherichia coli. J Clin Microbiol. 2005;43:2551-8.,1212 Mirelis B, Rivera A, Miró E, et al. A simple phenotypic method for differentiation between acquired and chromosomal AmpC β-lactamases in Escherichia coli. Enferm Infecc Microbiol Clín. 2006;24:370-2.

Three multiplex PCR and one simplex PCR were performed to determine the presence of blaTEM, blaSHV, blaOXA-1-like and blaCTX-M genes in ESBL-producing isolates, and blaACC, blaFOX, blaMOX, blaDHA, blaLAT, blaCMY, blaMIR and blaACT genes in plasmid-mediated AmpC β-lactamase-producing isolates. PCR primers and procedures were performed as previously described.1313 Dallenne C, Da Costa A, Decre D, Favier C, Arlet G. Development of a set of multiplex PCR assays for the detection of genes encoding important beta-lactamases in Enterobacteriaceae. J Antimicrob Chemother. 2010;65:490-5.

Purification and sequencing of PCR products were carried out by Macrogen Inc. (Korea) and the types of β-lactamase genes were identified by comparison with the sequences in GenBank (http://www.ncbi.nlm.nih.gov/genbank/).

During the study, a total of 79 isolates resistant to β-lactams were recovered. The most frequent isolated bacterial species were Escherichia coli (39) followed by Klebsiella pneumoniae (9), Klebsiella oxytoca (7) Enterobacter aerogenes (7), Enterobacter cloacae (5) Proteus mirabilis (3), Pseudomonas aeruginosa (3), Citrobacter freundii (3), Proteus vulgaris (2), and Enterobacter koseri (1).

All isolates showed antimicrobial resistance to one or more β-lactam antibiotics, and among them, 73 were confirmed to be positive for β-lactamase/ESBL and six for AmpC β-lactamase production (see Table 1 for details).

Table 1
Resistance rate for the clinical isolates.

By PCR amplification, it was found that 31% of the samples showed the presence of one β-lactamase gene, whilst isolates often carried two (28%), three (20%), four (18%), and occasionally five (3%) different variants of β-lactamase enzymes (see Table 2 for details).

Table 2
Summary of β-lactamase encoding genes detected in ESBL-producing bacteria from clinical isolates.

The genes encoding CTX-M were the most common and were found in 63 of the 73 ESBL-producing isolates. In particular the genes blaCTX-M belonging to phylogenetic groups 1, 2 and 9 were found in 48, 4 and 20 isolates, respectively. It was also detected that 52 of the ESBL-producing isolates carried blaTEM, 21 blaSHV, and 34 blaOXA-1-like genes. Finally, blaDHA was the most frequently observed plasmid-mediated AmpC β-lactamase gene (found in four isolates), while one isolate carried blaLAT and one blaMOX. To identify the specific bla genes detected in the PCR assays, amplicons DNA sequence analyses were performed and the results are summarized in Table 2.

Many studies on the resistance to β-lactams conducted in South America were performed using mainly a phenotypic approach. In Ecuador the few reports published on this topic lack almost totally of a genotypic study,1414 Salles MJ, Zurita J, Mejia C, Villegas MV. Resistant Gram-negative infections in the outpatient setting in Latin America. Epidemiol Infect. 2013;141:2459-72.

15 Eisenberg JN, Goldstick J, Cevallos W, et al. In-roads to the spread of antibiotic resistance: regional patterns of microbial transmission in northern coastal Ecuador. J R Soc Interface. 2012;9:1029-39.

16 Zurita J. Urinary E. coli: resistance trend in Ecuador from 1999 to 2007. Rev Ecuat Ginecol Obstet. 2009;15:29-35.
-1717 Nordberg V, Quizhpe Peralta A, Galindo T, et al. High proportion of intestinal colonization with successful epidemic clones of ESBL-producing Enterobacteriaceae in a neonatal intensive care unit in Ecuador. PLoS ONE. 2013;8:e76597. and, to the best of our knowledge, this is one of the first studies describing the genetic characteristics of β-lactamases in this country.88 Bonelli RR, Moreira BM, Picao RC. Antimicrobial resistance among Enterobacteriaceae in South America: history, current dissemination status and associated socioeconomic factors. Drug Resist Updat. 2014;17:24-36.,99 CLSI. Performance standards for antimicrobial susceptibility testing. 22nd informational supplement. CLSI document M100-S22. Wayne, PA: Clinical and Laboratory Standards Institute; 2012.,1717 Nordberg V, Quizhpe Peralta A, Galindo T, et al. High proportion of intestinal colonization with successful epidemic clones of ESBL-producing Enterobacteriaceae in a neonatal intensive care unit in Ecuador. PLoS ONE. 2013;8:e76597.

Our data confirmed the prevalence in Loja province of E. coli and Klebsiella spp. as β-lactamase producers,66 Canton R. Epidemiology and evolution of beta-lactamases. In: Baquero FNC, Cassell G, Gutiérrez-Fuentes J, editors. Evolutionary biology of bacterial and fungal pathogens. Washington: ASM Press; 2008. p. 249–70.,1818 Peirano G, Pitout JD. Molecular epidemiology of Escherichia coli producing CTX-M beta-lactamases: the worldwide emergence of clone ST131 O25:H4. Int J Antimicrob Agents. 2010;35:316-21. and a predominance of ESBL producers, showing the highest resistance levels mainly against cefotaxime, ciprofloxacin, netilmicin, and ampicillin.

It is widely documented that in South America ESBL-producing Enterobacteriaceae have one of the highest incidence in the world and CTX-Ms are the most broadly distributed.99 CLSI. Performance standards for antimicrobial susceptibility testing. 22nd informational supplement. CLSI document M100-S22. Wayne, PA: Clinical and Laboratory Standards Institute; 2012. In particular the type CTX-M-2 is the most frequent in the Southern Cone,1919 Radice M, Power P, Di Conza J, Gutkind G. Early dissemination of CTX-M-derived enzymes in South America. Antimicrob Agents Chemother. 2002;46:602-4. CTX-M-2-group, CTX-M-8, and CTX-M-9 in Brazil,2020 da Silva KC, Lincopan N. Epidemiology of extended-spectrum beta-lactamases in Brazil: clinical impact and implications for agribusiness. J Bras Patol Med Lab. 2012;48:91-9. CTX-M-1-group in Colombia,2121 Villegas MV, Correa A, Perez F, et al. CTX-M-12 beta-lactamase in a Klebsiella pneumoniae clinical isolate in Colombia. Antimicrob Agents Chemother. 2004;48:629-31. and CTX-M-2, CTX-M-14, CTX-M-15, CTX-M-24, and CTX-M-56 in Peru and Bolivia.2222 Pallecchi L, Bartoloni A, Fiorelli C, et al. Rapid dissemination and diversity of CTX-M extended-spectrum beta-lactamase genes in commensal Escherichia coli isolates from healthy children from low-resource settings in Latin America. Antimicrob Agents Chemother. 2007;51:2720-5.

In our study, it is documented that CTX-M enzymes are the dominant ESBLs in the Loja province, and among them the prevailing types are CTX-M-15 and CTX-M-14. These data are consistent with the literature2121 Villegas MV, Correa A, Perez F, et al. CTX-M-12 beta-lactamase in a Klebsiella pneumoniae clinical isolate in Colombia. Antimicrob Agents Chemother. 2004;48:629-31.,2222 Pallecchi L, Bartoloni A, Fiorelli C, et al. Rapid dissemination and diversity of CTX-M extended-spectrum beta-lactamase genes in commensal Escherichia coli isolates from healthy children from low-resource settings in Latin America. Antimicrob Agents Chemother. 2007;51:2720-5. as these two variants are present and quite frequent in Ecuador neighboring countries. Interestingly, the types CTX-M-55 and CTX-M-65 were detected. Actually, these variants are common in East Asia,2323 Qu F, Ying Z, Zhang C, et al. Plasmid-encoding extended-spectrum β-lactamase CTX-M-55 in a clinical Shigella sonnei strain, China. Future Microbiol. 2014;9:1143-50.,2424 Yin J, Cheng J, Sun Z, et al. Characterization of two plasmid-encoded cefotaximases found in clinical Escherichia coli isolates: CTX-M-65 and novel enzyme, CTX-M-87. J Med Microbiol. 2009;58:811-5. and one possible hypothesis of their presence in Southern Ecuador can be related to the recent immigration from China and the trade relationship between Ecuador and China.2525 Ellis RE. El impacto de China en Ecuador y América Latina. Observatorio Virtual Asia Pacifico; 2007 http://asiapacifico.utadeo.edu.co/wp-content/files/impactochina ecuador.pdf
http://asiapacifico.utadeo.edu.co/wp-con...
As expected, a strong presence of TEM-type β-lactamases was also found, in particular TEM-1 β-lactamase. TEM-type presents a wide geographical distribution, and in Ecuador these data are not particularly surprising considering the incidence of TEM in neighboring Colombia2626 Villegas MA, Correa A, Perez F, Miranda MC, Zuluaga T, Quinn JP. Prevalence and characterization of extended-spectrum β-lactamases in Klebsiella pneumoniae and Escherichia coli isolates from Colombian hospitals. Disease. 2004;49:217-22. and the trade and migratory flows between these two countries, as well as the recent intense Ecuadorian immigration to and from Europe and North America where TEM is predominant such as CTX-M-15. It is worth to mention the finding of one isolate harboring TEM-12. This ESBL variant has been already found in South America2727 Paterson DL, Hujer KM, Hujer AM, et al. Extended-spectrum beta-lactamases in Klebsiella pneumoniae bloodstream isolates from seven countries: dominance and widespread prevalence of SHV- and CTX-M-type beta-lactamases. Antimicrob Agents Chemother. 2003;47:3554-60. and it is one of the most common in North America.2828 Bush K. Extended-spectrum β-Lactamase in North America, 1987-2006. Clin Microbiol Infect. 2008;14:134-43. In our study, the presence of the non-ESBL OXA-1-type, SHV-1 and SHV-11, mainly found in Klebsiella (9 isolates) and Proteus (4 isolates), and the ESBL SHV-2 and SHV-12, found in Enterobacter, Klebsiella and E. coli, were also detected. The non-ESBL OXA-1-type and SHV-1 are among the most widespread in Enterobacteriaceae,2929 Livermore DM. β-Lactamase in laboratory and clinical resistance. Clin Microbiol Rev. 1995;8:557-84. while to the best of our knowledge SHV-11 variant is emergent in South America. Regarding ESBLs, the variants found in this study are among the most common in Latin America, indeed SHV-2 with SHV-5 were the first ESBL SHV-types described in Enterobacteriaceae,3030 Guzmán-Blanco M, Casellas JM, Sader HS. Bacterial resistance to antimicrobial agents in Latin America. The giant is awaking. Infect Dis Clin N Am. 2000;14:67-81. while SHV-12 is highly prevalent in Mexico, Colombia, and Brazil.3131 Guzmán-Blanco M, Labarca JA, Villegas MV, Gotuzzo E. Extended spectrum β-lactamase producers among nosocomial Enterobacteriaceae in Latin America. Braz J Infect Dis. 2014;18:421-33. Concerning AmpC β-lactamase, there is not sufficient data to draw significant conclusions on its epidemiology, but it is interesting to note the presence of two CMY-75 genes found in C. freundii. This variant has been already detected in C. freundii in Spain (EMBL/GenBank/DDBJ databases: AFK73434.1), but is emergent in South America. On the other hand DHA-1 has been previously recognized in South America, being quite predominant in Argentina.3232 Cejas D, Fernandez-Canigia L, Quinteros M, et al. Plasmid-encoded AmpC (pAmpC) in Enterobacteriaceae epidemiology of microorganisms and resistance makers. Rev Arg Microbiol. 2012;44:182-6.

In conclusion, in this work the predominance of ESBLs in Southern Ecuador was demonstrated with a prevalence of CTX-M-type enzymes and we identified two emergent variants in South America. A high presence of TEM-type β-lactamases were also detected, being TEM-1 β-lactamase the most frequent variant found. However, there are some limitations in this study, including the low number of isolates and the restricted geographical area of sampling. In order to minimize these problems and gather more indicative information on molecular epidemiology and genetic characteristics of β-lactamases within the entire territory of Ecuador, further isolates from different health institutions and regions of Ecuador have to be collected and characterized.

  • 1
    These authors contributed equally to this work.

Acknowledgements

This work was supported by the Project PROY_CCSAL_1042 of UTPL and by the Prometeo Project of the Secretariat for Higher Education, Science Technology and Innovation of the Republic of Ecuador.

References

  • 1
    Jansen WT, van der Bruggen JT, Verhoef J, Fluit AC. Bacterial resistance: a sensitive issue complexity of the challenge and containment strategy in Europe. Drug Resist Updat. 2006;9:123-33.
  • 2
    Magiorakos AP, Srinivasan A, Carey RB, et al. Multidrug-resistant, extensively drug-resistant and pandrug-resistant bacteria: an international expert proposal for interim standard definitions for acquired resistance. Clin Microbiol Infect. 2012;18:268-81.
  • 3
    Dantas G, Sommer MO, Oluwasegun RD, Church GM. Bacteria subsisting on antibiotics. Science. 2008;320:100-103.
  • 4
    Paterson DL, Bonomo RA. Extended-spectrum beta-lactamases: a clinical update. Clin Microbiol Rev. 2005;18:657-86.
  • 5
    Bradford PA. Extended-spectrum beta-lactamases in the 21st century: characterization, epidemiology, and detection of this important resistance threat. Clin Microbiol Rev. 2001;14:933-51.
  • 6
    Canton R. Epidemiology and evolution of beta-lactamases. In: Baquero FNC, Cassell G, Gutiérrez-Fuentes J, editors. Evolutionary biology of bacterial and fungal pathogens. Washington: ASM Press; 2008. p. 249–70.
  • 7
    Jones RN, Guzman-Blanco M, Gales AC, et al. Susceptibility rates in Latin American nations: report from a regional resistance surveillance program (2011). Braz J Infect Dis. 2013;17:672-81.
  • 8
    Bonelli RR, Moreira BM, Picao RC. Antimicrobial resistance among Enterobacteriaceae in South America: history, current dissemination status and associated socioeconomic factors. Drug Resist Updat. 2014;17:24-36.
  • 9
    CLSI. Performance standards for antimicrobial susceptibility testing. 22nd informational supplement. CLSI document M100-S22. Wayne, PA: Clinical and Laboratory Standards Institute; 2012.
  • 10
    Drieux L, Brossier F, Sougakoff W, Jarlier V. Phenotypic detection of extended-spectrum beta-lactamase production in Enterobacteriaceae: review and bench guide. Clin Microbiol Infect. 2008;14(Suppl. 1):90-103.
  • 11
    Yagi T, Wachino J, Kurokawa H, et al. Practical methods using boronic acid compounds for identification of class C beta-lactamase-producing Klebsiella pneumoniae and Escherichia coli J Clin Microbiol. 2005;43:2551-8.
  • 12
    Mirelis B, Rivera A, Miró E, et al. A simple phenotypic method for differentiation between acquired and chromosomal AmpC β-lactamases in Escherichia coli Enferm Infecc Microbiol Clín. 2006;24:370-2.
  • 13
    Dallenne C, Da Costa A, Decre D, Favier C, Arlet G. Development of a set of multiplex PCR assays for the detection of genes encoding important beta-lactamases in Enterobacteriaceae. J Antimicrob Chemother. 2010;65:490-5.
  • 14
    Salles MJ, Zurita J, Mejia C, Villegas MV. Resistant Gram-negative infections in the outpatient setting in Latin America. Epidemiol Infect. 2013;141:2459-72.
  • 15
    Eisenberg JN, Goldstick J, Cevallos W, et al. In-roads to the spread of antibiotic resistance: regional patterns of microbial transmission in northern coastal Ecuador. J R Soc Interface. 2012;9:1029-39.
  • 16
    Zurita J. Urinary E. coli: resistance trend in Ecuador from 1999 to 2007. Rev Ecuat Ginecol Obstet. 2009;15:29-35.
  • 17
    Nordberg V, Quizhpe Peralta A, Galindo T, et al. High proportion of intestinal colonization with successful epidemic clones of ESBL-producing Enterobacteriaceae in a neonatal intensive care unit in Ecuador. PLoS ONE. 2013;8:e76597.
  • 18
    Peirano G, Pitout JD. Molecular epidemiology of Escherichia coli producing CTX-M beta-lactamases: the worldwide emergence of clone ST131 O25:H4. Int J Antimicrob Agents. 2010;35:316-21.
  • 19
    Radice M, Power P, Di Conza J, Gutkind G. Early dissemination of CTX-M-derived enzymes in South America. Antimicrob Agents Chemother. 2002;46:602-4.
  • 20
    da Silva KC, Lincopan N. Epidemiology of extended-spectrum beta-lactamases in Brazil: clinical impact and implications for agribusiness. J Bras Patol Med Lab. 2012;48:91-9.
  • 21
    Villegas MV, Correa A, Perez F, et al. CTX-M-12 beta-lactamase in a Klebsiella pneumoniae clinical isolate in Colombia. Antimicrob Agents Chemother. 2004;48:629-31.
  • 22
    Pallecchi L, Bartoloni A, Fiorelli C, et al. Rapid dissemination and diversity of CTX-M extended-spectrum beta-lactamase genes in commensal Escherichia coli isolates from healthy children from low-resource settings in Latin America. Antimicrob Agents Chemother. 2007;51:2720-5.
  • 23
    Qu F, Ying Z, Zhang C, et al. Plasmid-encoding extended-spectrum β-lactamase CTX-M-55 in a clinical Shigella sonnei strain, China. Future Microbiol. 2014;9:1143-50.
  • 24
    Yin J, Cheng J, Sun Z, et al. Characterization of two plasmid-encoded cefotaximases found in clinical Escherichia coli isolates: CTX-M-65 and novel enzyme, CTX-M-87. J Med Microbiol. 2009;58:811-5.
  • 25
    Ellis RE. El impacto de China en Ecuador y América Latina. Observatorio Virtual Asia Pacifico; 2007 http://asiapacifico.utadeo.edu.co/wp-content/files/impactochina ecuador.pdf
    » http://asiapacifico.utadeo.edu.co/wp-content/files/impactochina ecuador.pdf
  • 26
    Villegas MA, Correa A, Perez F, Miranda MC, Zuluaga T, Quinn JP. Prevalence and characterization of extended-spectrum β-lactamases in Klebsiella pneumoniae and Escherichia coli isolates from Colombian hospitals. Disease. 2004;49:217-22.
  • 27
    Paterson DL, Hujer KM, Hujer AM, et al. Extended-spectrum beta-lactamases in Klebsiella pneumoniae bloodstream isolates from seven countries: dominance and widespread prevalence of SHV- and CTX-M-type beta-lactamases. Antimicrob Agents Chemother. 2003;47:3554-60.
  • 28
    Bush K. Extended-spectrum β-Lactamase in North America, 1987-2006. Clin Microbiol Infect. 2008;14:134-43.
  • 29
    Livermore DM. β-Lactamase in laboratory and clinical resistance. Clin Microbiol Rev. 1995;8:557-84.
  • 30
    Guzmán-Blanco M, Casellas JM, Sader HS. Bacterial resistance to antimicrobial agents in Latin America. The giant is awaking. Infect Dis Clin N Am. 2000;14:67-81.
  • 31
    Guzmán-Blanco M, Labarca JA, Villegas MV, Gotuzzo E. Extended spectrum β-lactamase producers among nosocomial Enterobacteriaceae in Latin America. Braz J Infect Dis. 2014;18:421-33.
  • 32
    Cejas D, Fernandez-Canigia L, Quinteros M, et al. Plasmid-encoded AmpC (pAmpC) in Enterobacteriaceae epidemiology of microorganisms and resistance makers. Rev Arg Microbiol. 2012;44:182-6.

Publication Dates

  • Publication in this collection
    Nov-Dec 2016

History

  • Received
    7 Apr 2016
  • Accepted
    12 July 2016
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