Journal of Pure and Applied MicrobiologyVol. 6 No. Special Edition Oct. 2012

An Algorithm for Detection of Extended Spectrum, AMP C and Metallo Beta Lactamases in Clinical Isolates: A Proactive Approach

Meher Rizvi, Nazish Fatima, M.W.Rizvi, Mehvash Haider, Indu Shukla, Abida Malik and Ayesha Usman

Department of Microbiology, JN Medical College, AMU, Aligarh, India.

Received on 04 March 2012 and accepted on 10 June 2012



With the increasing incidence in extended spectrum, AmpC beta lactamases and metallo beta lactamases in gram negative bacilli, diagnostic microbiology laboratories may soon be called upon to actively detect these drug resistance markers to allow both correct and timely treatment. We developed an efficient, simple and cost effective algorithm for phenotypic identification of these drug resistance markers within an acceptable turn around time. Samples received in the Clinical Bacteriology Laboratory were processed for culture and sensitivity. Gram negative bacilli were screened and confirmed for the presence of ESBL by double disk synergy test by using cefoperazone-sulbactum, piperacillin-tazobactum and ceftazidime-clavulanic acid during routine antibiotic susceptibility testing. Imipenem and cefoxitin were utilized for induction of suspected AmpC producers, when needed, by disk approximation assay on the second day. MBL production was confirmed by modified Hodge Test and Imipenem-EDTA double disk synergy test on the third day in strains resistant to imipenem. Among 251 isolates studied, 138 (54.98%) were ESBL producers, 101 (40.23%) were Amp C producers and 52 (20.71%) were MBL producers. Highest rates of detection of ESBL was by cefoperazone-sulbactam (109/138) 78.98% followed by piperacillin-tazobactam (58/138) 42.02% and ceftazidime -clavulanic acid (20/138). The highest ESBL producers were Acinetobacter spp. (100%), followed by Klebsiella spp (86.7%) and Proteus species (85.7%). AmpC production was detected in 72 (71.3%) members of the family Enterobacteriaceae, of which the most common were Citrobacter spp. (68%), followed by Proteus spp. (54.1%). Of 101 of the Amp C producing strains 20 (19.80%) were inducible and 81 were stably derepressed (80.19%). Imipenem was a better inducer of AmpC than cefoxitin. 52 (20.71%) isolates were identified as MBL producers, the highest number being of Pseudomonas aeruginosa followed by E. coli and Klebsiella spp. Among the methods employed for detection of MBL production, Hodge test (80%) proved better than DDST (55%). Of all the isolates studied, 40 isolates exhibited multiple mechanisms of resistance. High level of antibiotic resistance as observed in this study merits a proactive approach in detection of ESBL, AmpC and MBL in Gram negative bacteria to enable timely management of patient and also reduce period of hospital stay. We have developed an effective and simple approach to identify these resistance markers.

Keywords : Extended spectrum beta lactamases, AmpC beta lactamases and metallo beta lactamases.