Occurrence & detection of AmpC beta-lactamases at a referral hospital in Karnataka

AmpC beta-lactamases confer resistance to a wide variety of beta-lactam drugs except for cefepime, cefpirome and carbapenems. They are known to be responsible for nosocomial outbreaks, therapeutic failures and multidrug resistance. Although reported with increasing frequency the true rate of occurrence of these beta-lactamases in Enterobacteriaceae is not known. Hence the present study was undertaken to determine the occurrence of AmpC enzymes among clinical isolates.

A total of 520 consecutive, non-repeat clinical isolates were included in the present study. Twenty eight strains resistant to cefoxitin were tested for AmpC beta-lactamases by the modified 3-dimensional extract method. Isolates harbouring AmpC beta-lactamases were tested for inducible beta-lactamases by disc diffusion.

Sixteen (3.3%) isolates were positive for AmpC beta-lactamases. Based on the species 9 (3.3%) Escherichia coli, 4 (2.2%) Klebsiella pneumoniae, 2 (5%) Citrobacter freundii and 1 (5.5%) isolate of Enterobacter aerogenes harboured AmpC enzymes. Nine (56.3%) of AmpC harbouring strains, were urinary isolates. All the isolates were sensitive to imipenem and variably sensitive to aminoglycosides and co-trimoxazole.

Our findings document the presence of AmpC enzymes in this region. Hence AmpC beta-lactamase detection should be undertaken in clinical isolates showing resistance to broad-spectrum cephalosporins.