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 by Acinetobacter baumannii often prove difficult to treat owing to their multiple drug resistance. Carbapenems play a pivotal role in the management of severe Acinetobacter infections. However, reports of carbapenem resistance have been increasing alarmingly due to production of a variety of carbapenemases including metallo-b-lactamases (MBLs). This study investigated by both phenotypic and genotypic assays the prevalence of MBLs in a total of 55 A. baumannii strains 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, bla IMP1 and bla VIM2 , 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 mg ml "1 ) for meropenem. Thirty-nine isolates (70.9 %) were positive for MBL production by the DDS test while bla IMP1 gene amplification was seen only in 23 isolates (42 %). Interestingly, none of the isolates showed amplification of bla VIM2 . 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 among Acinetobacter spp. in India.

Comparison of Various Phenotypic Methods in Detection of Carbapenemases and Metallo-Beta-Lactamases in Carbapenem Resistant Clinical Isolates of Acinetobacter Species at a Tertiary Care Centre in North India

“…Overall MBL production was found quite significant 88% (88/100) among our isolates close to a study by Uma et al, (2009) reporting 70.9 % MBL production. Another Indian study by Shanthi et al, (2009) According to Yong et al, (2002), the imipenem (IMP) 10 μg-EDTA 750 μg combined disc test has 95.7% sensitivity and 91.0% specificity for detection of metallo-β-lactamases in MBL-producing Ps.…”

blaIMP and blaVIM mediated carbapenem resistance in Pseudomonas and Acinetobacter species in India

“…In India, MBL production among A. baumannii isolates has been reported at 42%. The most prevalent MBL gene was bla IMP-1 [15]. There is limited data on the prevalence and distribution of metallo-beta-lactamases among Indian isolates.…”

“…Hence MHT was positive in 169 isolates (94.4%). The remaining 10 were MHT negative, thereby suggestive of other mechanisms such as loss of porins or upregulation of efflux pumps [15].…”

“…In recent years there has been an increase in carbapenem resistance among Gramnegative bacteria in the Indian subcontinent [12,13,14]. Resistance mechanisms include lack of drug penetration (i.e., porin mutations and efflux pumps) and/or carbapenem hydrolysingbetalactamase enzymes [2,15,16]. Over the past few years MBL producing isolates have emerged worldwide and are associated with outbreaks in health-care settings.…”

Antibiotic Sensitivity Pattern of Blood Isolates of <i>Acinetobacter</i> Species in a Tertiary Care Hospital: A Retrospective Analysis

“…In our study the level of carbapenem resistance was very high in the Baumanii group. Karthika et al (2009) in their study showed the presence of bla IMP1 carbapenemase genes in South Indian population. Though bla VIM-2 is the most common carbapenemases seen in other parts of world (Yum et al, 2002;Poirel et al, 2000;Walsh et al, 2005), it was surprisingly absent in their study, though bla IMP1 gene was seen in 42% of isolates (Karthika et al, 2009).…”