Phenotypic and genotypic assays for detecting the prevalence of metallo-β-lactamases in clinical isolates of Acinetobacter baumannii from a South Indian tertiary care hospital

Abstract

Nosocomial infections caused byAcinetobacter baumanniioften prove difficult to treat owing to their multiple drug resistance. Carbapenems play a pivotal role in the management of severeAcinetobacterinfections. However, reports of carbapenem resistance have been increasing alarmingly due to production of a variety of carbapenemases including metallo-β-lactamases (MBLs). This study investigated by both phenotypic and genotypic assays the prevalence of MBLs in a total of 55A. baumanniistrains isolated from a South Indian tertiary care hospital. Random amplified polymorphic DNA (RAPD) genotyping and antimicrobial susceptibility testing for nine clinically relevant antibiotics was done for characterization of isolates. Phenotypic expression of MBLs was examined by a simple double disc synergy (DDS) test, and the presence of the most frequent MBL coding genes,blaIMP1andblaVIM2, was checked by PCR. RAPD analysis generated six clusters of isolates and there was very little correlation between RAPD clusters and resistant profiles. Most of the isolates showed complete or high resistance to imipenem (100 %), meropenem (89 %), amikacin (80 %), cefotaxime (89 %) and ciprofloxacin (72 %). In addition, 44 % of isolates showed a high MIC level (≥16 μg ml−1) for meropenem. Thirty-nine isolates (70.9 %) were positive for MBL production by the DDS test whileblaIMP1gene amplification was seen only in 23 isolates (42 %). Interestingly, none of the isolates showed amplification ofblaVIM2. Further investigations on DDS-positive/PCR-negative isolates by spectrophotometric assay showed MBL activity in most of the isolates, suggesting involvement of other genes. The high incidence of isolates possessing MBL activity in the present study represents an emerging threat of complete resistance to carbapenems amongAcinetobacterspp. in India.