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Detection of Amp-C Beta lactamase enzyme production among Enterobacteriaceae and comparison of different inducer substrate combinations for detection of inducible Amp-C

AmpC beta-lactamases hydrolyse penicillins, monobactams, cephalosporins and cephamycins. AmpC producers are resistant tobetalactam/betalactamase inhibitor combinations therapeutically. AmpC is generally underreported which leads to therapeutic failures and uncontrolled spread of these resistant strains. Hence, there is an increased need to detect AmpC routinely in the laboratory. To detect AmpC β-lactamase production among Enterobacteriaceae isolated from clinical samples and to compare different inducer substrate combinations for the detection of inducible Amp-C (iAmpC). 100 clinical isolates of Enterobacteriaceae were tested. Constitutive AmpC (cAmpC) detected using inhibitor based method using Cefoxitin (CN) and CN with Phenylboronic acid (PBA). Inducible AmpC detected using disk approximation test using inducers Imipenen (I) and Cefoxitin (CN), and substrates Cefotaxime (CTX), Ceftazidime (CAZ) and PiperacillinTazobactum (PT). Various combinations tested were I/PT, I/CTX, I/CAZ, CN/CTX, CN/CAZ. AmpC production was detected in 30% of isolates, 23% were constitutive and 7% were inducible. Commonest AmpC producer was Enterobacter sp with 7(36.84%) and 4(21.05%), followed by E. coli 14(26.92%) and 3(5.76%) constitutive and iAmpC respectively. 2(8.69%) Klebsiella demonstrated only cAmpC. I/PT combination detected all the 7 iAmpC, others I/CTX and I/CAZ detected only 3isolates. Simple disk method of cefoxitin with boronic acid and I/PT combination can be used to detect constitutive and inducible AmpC respectively. | Detection of Amp-C Beta lactamase enzyme production among Enterobacteriaceae and comparison of different inducer substrate combinations for detection of inducible Amp-C