Prevalence of AmpC Beta-lactamase in Gram Negative Bacilli by Different Phenotypic Methods in a Tertiary Care Institute in Kashmir

Abstract

Context: AmpC type cephalosporinases are Ambler class C β-lactamases. They hydrolyze penicillins, cephalosporins; except the fourth-generation compounds and monobactams. To the best of our knowledge prevalence of AmpC in our hospital is not known.    Aims: With this background the study was undertaken to detect the prevalence of AmpC lactamases in gram-negative bacilli at our institute. We also performed four different tests, i.e. AmpC disc test, modified Hodge test, modified three dimensional spot inoculation test on a single agar plate (three in one) and inhibitor based test using boronic acid for detecting AmpC production. Methods and Materials: Screening for AmpC was done by using cefoxitin discs. Organisms resistant to cefoxitin were tested for presence of AmpC by AmpC disc test, Modified Hodge test, Three dimensional spot inoculation test and Boronic acid disc test. Statistical Analysis: Statistical analysis was done by Chi Square test and Fishers Exact Test with the SPSS statistical programme (version 20.0).     Results: A total of 1323 non duplicate Gram negative bacilli were isolated during a period of one year in the Department of microbiology SKIMS. Out of these 1323 isolates, 150 isolates were found to be resistant to cefoxitin and one or more third generation cephalosporin antibiotics or showed antagonism between cefoxitin and cefotaxim discs thus fulfilling the criteria and were included in the present study. Forty five (3.4%) were positive for AmpC beta lactamases. Boronic acid test detected 38 (25.3%), AmpC disc test 35 (23.3%), MHT 29 (19.3%) and MTDST detected 27 (18%). Conclusions: Inhibitor based test using boronic acid detected the maximum number of AmpC producing organisms. It is a simple and cost effective test that can be incorporated in routine susceptibility testing plate thus saving time also.