Prevalence of carbapenem-hydrolyzing OXA-type β-lactamases among Acinetobacter baumannii in patients with severe urinary tract infection

Abstract

Acinetobacter baumannii produces carbapenemase-hydrolyzing class D β-lactamases (CHDLs) as one of the major drug resistance mechanisms. This investigation is thus aimed to assess the prevalence and to characterize the CHDL-producing strains of A. baumannii by both phenotypic assays and genotypic characterization. A total of 73 isolates of A. baumannii were phenotypically and genotypically characterized from patients (N = 1,000) with severe urinary tract infection. Tested strains were subjected to double disk synergy testing by Kirby-Bauer disk diffusion method with modified Hodge test (MHT) for carbapenemase production. Plasmid DNA was molecularly screened for CHDL-encoding blaoxa-51, blaoxa-23, and blaoxa-143 genes by polymerase chain reaction. Carbapenem-resistant profile showed 100%, 61.64%, and 67.12% resistance by Kirby-Bauer disk diffusion method that correlated with MHT positivity for 100% (n = 73), 80% (n = 36), and 78% (n = 38) of the isolates against imipenem, doripenem, and meropenem, respectively. The blaoxa-51 and blaoxa-23 were observed in 41.09% (n = 30) and 35.61% (n = 26) with co-occurrence in 4.10% (n = 3) of the isolates. MHT-positive isolates showed 100%, 91.66%, and 71.4% for blaoxa-51 and 91.78%, 51.11%, and 34.69% for blaoxa-23 with imipenem, doripenem, and meropenem resistance, respectively. None of the strains yielded blaoxa-143 gene. The findings of this study showed prevalence of carbapenem resistance and high frequency of blaoxa-51 and blaoxa-23 among A. baumannii.