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

• Published in: Indian journal of medical microbiology 2012-04, Vol.30 (2), p.170-174
• Main Authors: Buchunde, S, Mendiratta, DK, Deotale, V, Narang, P
• Format: Article
• Language: English
• Subjects: Antibiotics; disc potentiation test; Double-disc synergy test; EDTA-phenanthroline-Imipenem/Meropenem Broth Microdilution; Metallo-β-lactamase; P. aeruginosa; PCR; Pseudomonas aeruginosa
• ISSN: 0255-0857
• DOI: 10.4103/0255-0857.96683

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.