Abstract
BackgroundProductions of metallo-β-lactamases enzymes are the most common mechanism of antibiotic resistance to all beta-lactam classes (except monobactams) in Acinetobacter baumannii. MBLs are usually associated with gene cassettes of integrons and spread easily among bacteria. The current study was performed to detect the genes encoding MBLs and integron structures in A. baumannii isolates from burn patients.MethodsThis study was performed on 106 non-duplicate A. baumannii isolates from burn patients referred to Shahid Motahari Hospital in Tehran. Antibiotic susceptibility of A. baumannii isolates was performed using disk diffusion and broth microdilution method in accordance with the CLSI guidelines. The presence of class 1 integron and associated gene cassettes as well as MBLs-encoding genes including blaVIM, and blaIMP were investigated using PCR and sequencing techniques.ResultsIn this cross-sectional study all (100%) of the A. baumannii isolates examined were multidrug resistant. All isolates were sensitive to colistin and simultaneously all were resistant to imipenem. PCR assays showed the presence of blaVIM and blaIMP genes in 102 (96.2%) and 62 (58.5%) isolates of A. baumannii respectively. In addition, 62 (58.5%) of the A. baumannii isolates carried integron class 1, of which 49 (79.0%) were identified with at least one gene cassette. Three types of integron class 1 gene cassettes were identified including: arr2, cmlA5, qacE1 (2300 bp); arr-2, ereC, aadA1, cmlA7, qacE1 (4800 bp); and aac(3)-Ic, cmlA5 (2250 bp).ConclusionA high prevalence of MBLs genes, especially blaVIM, was identified in the studied MDR A. baumannii isolates. In addition, most of the strains carried class 1 integrons. Furthermore, the gene cassettes arrays of integrons including cmlA5 and cmlA7 were detected, for the first time, in A. baumannii strains in Iran.
Highlights
Productions of metallo-β-lactamases enzymes are the most common mechanism of antibiotic resistance to all beta-lactam classes in Acinetobacter baumannii
The differences between variables were evaluated by the chi-square (χ2) test and P-values (P < 0.05) were interpreted statistically significant. In this cross-sectional study, a total of 106 non-duplicate A. baumannii isolates were collected from burn wounds of hospitalized patients
According to the results of antimicrobial susceptibility testing, all (100%) of our A. baumannii isolates were identified as MDR and 101 (95.3%) were Extensively-drug resistant (XDR), Pan-drug resistant (PDR) phenotype were not detected in any of the isolates
Summary
Productions of metallo-β-lactamases enzymes are the most common mechanism of antibiotic resistance to all beta-lactam classes (except monobactams) in Acinetobacter baumannii. The current study was performed to detect the genes encoding MBLs and integron structures in A. baumannii isolates from burn patients. Various mechanisms are involved in the development of carbapenem resistance in A. baumannii including β-lactamases acquisition, outer membrane proteins and PBPs alteration, overexpression of efflux pumps and gene mutation of CarO [6]. One of the most important mechanisms of antibiotic resistance in A. baumannii is the production of β-lactamase enzymes, the genes of which are usually carried on mobile genetic elements, including integrons [7]. Resistance to carbapenems is usually dependent on β-lactamases of class B (MBLs) and D (OXA-type carbapenemases) [9]. Previous studies have shown that the prevalence of MBL-producing strains of A. baumannii in the world is increasing, there are different reports in various geographical areas [13]
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