A hundred and six Pseudomonas aeruginosa isolates from clinical cases were screened using PCR for the presence of integrons and associated resistance gene cassettes. Forty-four isolates harboured class 1 integrons (41.5%), of which 29 isolates (66%) also carried gene cassettes. The aacA gene was most frequently found within class 1 integrons (69%), followed by blaOXA family genes (52%). From class 1 integron-positive strains, we detected a total of 15 isolates (34%) carrying no gene cassettes. Restriction fragment-length polymorphism analysis of the integrons variable region revealed some identical structures, as well as distinct profiles indicating heterogeneity among these cassette regions. Multiresistance was observed in 71% of isolates, nevertheless no strong correlation was observed between integron presence and multiresistance. This is the first report showing class 1 integron prevalence and gene cassette content in P. aeruginosa isolates from clinical settings in the Brazilian Amazon.

BackgroundCarbapenems are the antibiotics of choice to treat infections caused by Acinetobacter baumannii, and resistance to this class can be determined by loss of membrane permeability and enzymatic mechanisms. Here, we analyzed the basis of carbapenem resistance in clinical A. baumannii isolates from different Brazilian regions.ResultsThe analyses addressed the carbapenemase activity of OXA-23, CarO expression and alterations in its primary structure. Susceptibility test revealed that the strains presented the COS (Colistin-Only-Sensitive) profile. PCR and sequencing showed the presence of the chromosomally-encoded blaOXA-51 in all isolates. The majority of strains (53%) carried the carbapenemase blaOXA-23 gene associated with ISAba1. The Hodge test indicated that these strains are carbapenemase producers. PFGE revealed 14 genotypes among strains from Rio de Janeiro and Maranhão. The influence of carO on imipenem resistance was evaluated considering two aspects: the composition of the primary amino acid sequence; and the expression level of this porin. Sequencing and in silico analyses showed the occurrence of CarOa, CarOb and undefined CarO types, and Real Time RT-PCR revealed basal and reduced carO transcription levels among isolates.ConclusionsWe concluded that, in general, for these Brazilian isolates, the major carbapenem resistance mechanism was due to OXA-23 carbapenemase activity and that loss of CarO porin plays a minor role in this phenotype. However, it was possible to associate the carO alleles and their expression with imipenem resistance. Therefore, these findings underline the complexity in addressing the role of different mechanisms in carbapenem resistance and highlight the possible influence of CarO type in this phenotype.

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Nosocomial outbreaks caused by multidrug-resistant (MDR) Pseudomonas aeruginosa have been associated to fibrocystic patients and isolates harboring metallo-beta-lactamase (MBL) genes. Genotyping is an important tool for interpreting bacterial nosocomial outbreaks and implementing adequate control strategies. The aim of this study was to evaluate whether an outbreak of MDR P. aeruginosa occurring in different hospitals was due to a unique clone or independent isolates. From 2000 to 2003, 108 P. aeruginosa were recovered from colonized/infected inpatients in hospitals of São Luís, Maranhão, Brazil. The susceptibility test was performed with antipseudomonal drugs, and the presence of MBL genes were verified by PCR. Isolates were genotyped by pulsed-field gel electrophoresis (PFGE). The majority of strains was multiresistant including a great number presenting the colistin-only-sensitive (COS) profile. PFGE analysis revealed 54 genotypes, with predominance of three major COS clones (A, C, and E) coexisting at different moments and hospitals. Clone A harbored the bla(SPM) gene. Eight unique genotypes also had the COS profile. Other eight MDR genotypes presented isolates with differences in resistance profiles. Here we detected, for the first time, the coexistence of COS P.aeruginosa genotypes disseminated in several hospitals during long periods, attacking patients under various clinical conditions.