OXA-181 Beta Lactamase is not a Major Mediator of Carbapenem Resistance in Enterobacteriaceae.

Background: Detection of carbapenem hydrolyzing class D beta lactamase OXA-181, (a variant of OXA-48) in Enterobacteriaceae, is important, to institute appropriate therapy and to initiate preventive measures. This study was done to determine the presence of OXA 48 and its derivative OXA-181 in Enterobacteriaceae of pathogenic significance.

Material And Methods: One hundred and eleven non-repetitive Enterobacteriaceae isolates which were resistant to any of the cephalosporin subclasses III and which exhibited reduced susceptibility to carbapenems were included in the study. Minimum inhibitory concentrations (MICs) to imipenem and meropenem was determined by broth microdilution. Production of carbapenamase was screened by Modified Hodge test (MHT). Polymerase Chain Reaction (PCR) was done to detect the presence of bla OXA-181 and bla OXA-48 .Coexistence of other carbapenemase encoding genes, namely, NDM-1, VIM, IMP and KPC were also looked for, by PCR.

Results: Of all the isolates which were tested, only 2 (1.8%) revealed the presence of OXA-181 and OXA-48. These were Klebsiella pneumoniae and Citrobacter freundii. MICs of imipenem and meropenem for Klebsiella pneumoniae were 128mg/l and 64 mg/l and for Citrobacter freundii, they were 32mg/l and 16mg/l respectively. MHT was positive in both isolates.

Conclusion: Production of OXA-48 / OXA-181 is not a major mechanism of carbapenem resistance. PCR is the gold standard for its routine identification in clinical microbiology laboratory.