Detection of extended spectrum β-lactamase among gram negative clinical isolates from a tertiary care hospital in South India.

Background: The β lactamase enzymes produced by the organisms break down the structural beta-lactam ring of β lactam antibiotics. Many genera of gram negative bacteria possess a naturally occurring, chromosomally mediated β lactamase and also some are plasmid mediated β lactamases. The objective of the study was to detect extended spectrum β lactamases among gram negative clinical isolates. Methods: 200 clinical were subjected to routine disc diffusion technique and zone diameter of ≤27mm for Cefotaxime and ≤22mm for Ceftazidime or ≤25mm for Ceftriaxone were included in this study. The strains are subjected to double disc synergy test. Results: Of 200 samples, 174 yielded organisms belonging to enterobacteriaceae and 26 yielded growth of nonfermenters. Out of 174 members of enterobacteriaceae family, 122 were E. coli, 36 Klebsiella spp, 8 Proteus spp, 5 Enterobacter spp and 3 Citrobacter spp. Out of 26 nonfermenters, 18 were Pseudomonas spp and 8 were Acinetobacter. Conclusions: In the present study prevalence of ESBL was 23.3%, the high prevalence may be due to irrational use of third generation cephalosporins in both the hospital and community.

Comparison of disc and MIC reduction methods with polymerase chain reaction for the detection of metallo-β-lactamase in Pseudomonas aeruginosa.

Purpose: The present study was undertaken to evaluate the screening antibiotic, confirmatory phenotypic test and agent against PCR as gold standard and to detect the prevalent MBL gene. Materials and Methods: Three hundred and twenty-six Pseudomonas aeruginosa isolates were screened for resistance to Imipenem (IPM), Meropemem (MEM) and Ceftazidime (CAZ) by disc diffusion. Isolates resistant to any of these were considered screen test-positive for MBL and were subjected to Double disc synergy test (DDST) and Disc potentiation test (DPT: Using IPM, MEM and CAZ alone and with EDTA), Minimum inhibitory concentration (MIC) reduction [four-fold or more reduction in MIC of IPM and MEM in presence of chelators: EDTA and 1,10-phenanthroline (EPI/EPM: EDTA-phenanthroline- Imipenem/Meropenem Broth Microdilution method)] and polymerase chain reaction (PCR) for blaIMP and blaVIM . Results: Screen test-positives by MEM and CAZ were 19.3% as against 17.8% by IPM. MEMDDST, DPT and EPM confirmed 100% screen-test positives as against 93.7% by CAZ DDST and DPT-2, 76.2% by CAZ DPT-1, 88.9% by IPM DDST, 85.7% by IPM DPT-1 and 92.1% by EPI. IPMand CAZ DDST together confirmed 100% while IPM and CAZ DPT-2 confirmed 96.8%. All 63 screen-test positives showed the presence of blaVIM . Conclusions: MEM was found to be the best screening and confirmatory agent for MBL detection and blaVIM was found to be the prevalent MBL gene in this part of the country.