Carbapenem-resistant Acinetobacter baumannii from Brazil: role of carO alleles expression and blaOXA-23 gene

• Published in: BMC microbiology 2013-11, Vol.13 (1), p.245-245
• Main Authors: Fonseca, Erica Lourenço, Scheidegger, Erica, Freitas, Fernanda S, Cipriano, Rosângela, Vicente, Ana Carolina P
• Format: Article
• Language: English
• Subjects: Acinetobacter baumannii; Acinetobacter baumannii - drug effects; Acinetobacter baumannii - enzymology; Acinetobacter baumannii - genetics; Acinetobacter baumannii - isolation & purification; Acinetobacter Infections - microbiology; Allelomorphism; Amino Acid Sequence; Amino acids; Anti-Bacterial Agents - pharmacology; Bacterial genetics; Bacterial Outer Membrane Proteins - genetics; Bacterial Outer Membrane Proteins - metabolism; beta-Lactam Resistance; beta-Lactamases - genetics; beta-Lactamases - metabolism; Brazil; Carbapenems; Carbapenems - pharmacology; Colistin; DNA, Bacterial - chemistry; DNA, Bacterial - genetics; Drug resistance in microorganisms; Electrophoresis, Gel, Pulsed-Field; Genetic aspects; Genotype; Health aspects; Humans; Microbial Sensitivity Tests; Molecular Sequence Data; Molecular Typing; Phenotype; Polymerase Chain Reaction; Porins - genetics; Porins - metabolism; Sequence Analysis, DNA
• ISSN: 1471-2180; 1471-2180
• DOI: 10.1186/1471-2180-13-245

Carbapenems 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. The 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. We 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.