Out of 24 nosocomial strains of Pseudomonas aeruginosa from Recife, Brazil, 15 (62%) were metallo-beta-lactamase producers. Such isolates were resistant to main antipseudomonas drugs, except polymixyn B and aztreonam. The enzyme responsible for the carbapenem-resistance belongs to SPM-1 class, and the gene involved, blaspm-1, is likely plasmid located.
Pseudomonas aeruginosa; multidrug-resistance; metallo-beta-lactamase
De 24 linhagens hospitalares de Pseudomonas aeruginosa provenientes de Recife, Brasil, 15 (62%) produziram metalo-beta-lactamase. Tais isolados foram resistentes às principais drogas antipseudomonas, exceto polimixina B e aztreonam. A enzima responsável pela resistência aos carbapanêmicos pertence à classe SPM-1 e o gene envolvido, blaspm-1, provavelmente é plasmidial.
Pseudomonas aeruginosa; multiresistência a drogas; metalo-beta-lactamase
Metallo-b-lactamase producing Pseudomonas aeruginosa strains isolated in hospitals in Recife, PE, Brazil
Produção de metalo-b-lactase de linhagens de Pseudomonas aeruginosa isoladas em hospitais do Recife, PE, Brasil
Vera Magalhães; Ana Kelly Lins; Marcelo Magalhães* * Corresponding Author. Mailing address: Rua Sete de Setembro, 508, 50050-030. Recife, PE, Brasil. E-mail: email@example.com
Departamento de Medicina Tropical, Centro de Ciências da Saúde, Universidade Federal de Pernambuco, Recife, PE, Brasil
Out of 24 nosocomial strains of Pseudomonas aeruginosa from Recife, Brazil, 15 (62%) were metallo-b-lactamase producers. Such isolates were resistant to main antipseudomonas drugs, except polymixyn B and aztreonam. The enzyme responsible for the carbapenem-resistance belongs to SPM-1 class, and the gene involved, blaspm-1, is likely plasmid located.
Key words: Pseudomonas aeruginosa, multidrug-resistance, metallo-b-lactamase
De 24 linhagens hospitalares de Pseudomonas aeruginosa provenientes de Recife, Brasil, 15 (62%) produziram metalo-b-lactamase. Tais isolados foram resistentes às principais drogas antipseudomonas, exceto polimixina B e aztreonam. A enzima responsável pela resistência aos carbapanêmicos pertence à classe SPM-1 e o gene envolvido, blaspm-1, provavelmente é plasmidial.
Palavras-chave: Pseudomonas aeruginosa, multiresistência a drogas, metalo-b-lactamase
Since the early 1990s, the therapeutic problem posed by multidrug-resistant Pseudomonas aeruginosa gained interest on the recognition of nosocomial strains capable to produce metallo-b-lactamase (MbL). The prevalence of these strains is increasing in different parts of the world (3,9,11,16,18), including Brazil (4,12,13,17,19).
MbL enzymes are a cause of concern because they are able to hydrolyze most beta-lactams, including imipenem and meropenem, drugs considered of reserve for the treatment of Gram-negative multidrug-resistant strains (20). In addition, MbLs are encoded on genes linked to mobile elements, a condition that facilitates their spread among different bacterial species and genera (2). Presently, four distinct groups of MbLs have been recognized: IMP, observed in Japan (18), VIM, originally detected in Italy (8), GIM, detected in Germany (3), and finally, SPM-1, first detected in São Paulo, Brazil (19). As result of variations in their aminoacid sequences, IMP and VIM enzymes are classified in a still growing number of subgroups (20).
Here, we report the occurrence, susceptibility patterns, and MbL production of P. aeruginosa strains resistant to carbapenems isolated from hospitalized patients in Recife.
Between November 1, 2002 and February 25, 2003, we isolated 48 strains of P. aeruginosa at a clinical laboratory in Recife, Brazil. Twenty-two isolates were from Hospital Português, a large hospital in Recife, and 26 isolates came from smaller hospitals: Hospital das Clínicas, 8, Hospital Unicordis, 4, Hospital São Marcos, 6, and Hospital Santa Joana, 4. All strains were recovered from hospitalized individuals, most were old (mean age = 71.4 years) and debilitated with urinary tract infections or with respiratory problems undergoing ventilation. Only one isolate per patient was considered.
Cultures identification and antibiograms
Bacterial cultures were identified using conventional methods (7). Antibiotic susceptibility was determined by the disk diffusion method, according to NCCLS (10). Tests for polymixyn B, however, were done by using a previously suggested protocol (5). The following antipseudomonas drugs were tested: ceftazidime, gentamicin, piperacillin, amikacin, aztreonam, cefepime, ciprofloxacin, levofloxacin, imipenem, meropenem, tobramicin, and polymixyn B (Oxoid Limited, Hampshire, England). Strains of P. aeruginosa presenting intermediate or complete resistance to imipenem (inhibition zone < 16 mm) were screened for MbL production.
Screening for M b L production and b-lactamase gene identification
Screening was done employing two double disk-synergy techniques. One of them (1) uses as MbL inhibitor blank disks impregnated with 2 ml of undiluted 2-mercaptopropionic acid (2-MPA) solution (Aldrich Chemical Co, Milwaukee, USA) and as indicator, disks containing 30 mg of ceftazidime (Oxoid). An enhanced zone of inhibition between the disks was indicative of MbL production. The other technique (21) compares the sizes of the inhibition zones produced by two 10 mg disks of imipenem (Oxoid), with and without 750 mg of ethylenodiaminetetraacetic acid (EDTA); an increasing of at least 7 mm around the EDTA-imipenem disk was recorded as a positive result.
The identification of MbL coding genes was carried out by Patrice Nordmann (Hospital Bicêtre, Paris) using Polymerase chain reactions (15).
Among 48 isolates of P. aeruginosa obtained in this survey, 24 (50%) were resistant to imipenem. Of these, 15 (62.5%) were positive for MbL production on the screening tests (Table 1). Both EDTA and 2-MPA enzyme inhibitors were equally efficient for neutralizing MbL enzymes.
The imipenem-resistant strains were resistant to all drugs tested, except polymixyn B, independently of MbL production. This resistance pattern was similar to that found in Rio de Janeiro (12). Present data showed a higher percentage of MbL-producing P. aeruginosa strains in Recife than that found in other Brazilian cities (12,17). The multiplicity of antibiotic resistance gives to the imipenem-resistant strains a notable advantage for perpetuation and spreading in hospital settings, either carbapenems are or not being used, since they can be selected by a non-specific way (11).
All MbL-producing strains were susceptible to aztreonam, while all except one of the nine non-MbL-producers were resistant (Table 1). The incapacity of the metallo-enzymes to hydrolyze monobactams is well known (11,14); it would be the first indication for the presence of MbL-producing bacteria.
Studies done at Nordmann's laboratory in Paris, involving 11 MbL-producing P. aeruginosa strains of the present series, selected at random, indicated that their carbapenemase is encoded on the gene blaspm-1, the same gene previously identified in the strain 48-1997, isolated in São Paulo (19). This strain, like the isolates from Recife, carries blaspm-1 on a plasmid. In addition, genetic analysis showed that upstream blaspm-1 there is a novel common region (CR4) comprising an open reading frame, orf495, which may be responsible for eventual mobilization and expression of the resistance gene (13).
The gene blaspm-1 is restricted so far to P. aeruginosa from Brazilian hospitals. Nevertheless, SPM-1 is not the only metallo-enzyme circulating in the country. Recently, a clinical strain of Acinetobacter baumannii producing an IMP-like MbL was detected in a Brazilian teaching hospital (6).
In Recife, drug-resistance constitutes a serious medical menace. Antibiotics are freely sold and for costs saving many patients are prematurely discharged from hospitals to complete their treatment at home. These practices would provide an unwished bridge between hospital and community for the dissemination of genes coding for multiple resistance to antibiotics.
Submitted: April 14, 2004; Returned to authors for corrections: March 21, 2005; Approved: May 10, 2005
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Publication in this collection
16 Jan 2006
Date of issue
10 May 2005