Concurrent occurrence of Amp C and Cefotaxime (CTX)-M inclinical isolates of enterobacteriaceae

Abstract

Enterobacteriaceae producing both Amp C beta lactamases and extended-spectrum beta lactamases (ESBLs) have been increasingly reported worldwide. While the phenotypic tests for ESBL is standardised and used widely, it is not so for Amp C. When they coexist they may mask each other's detection phenotypically. We undertook this study to detect the concurrent occurrence of Cefotaxime (CTX)-M and plasmid Amp C in clinical isolates of Enterobacteriaceae by phenotypic and genotypic methods. One hundred clinically significant isolates of Escherichia coli (E. coli; 43), Klebsiella pneumoniae (K. pneumoniae; 43) and Proteus mirabilis (P. mirabilis; 14) were included in the study. Antibiotic susceptibility testing to various classes of antimicrobials was performed by disc diffusion using Clinical Laboratory Standards Institute (CLSI) guidelines. Isolates were screened for production of ESBL by CLSI method and Amp C beta lactamase by inhibitor based method using boronic acid and cloxacillin. Polymerase chain reaction (PCR) was performed for the detection of plasmid Amp C genes and blaCTX-M . Plasmid Amp C genes were detected in 27 isolates which included CIT (Origin Citrobacter freundii): 14; DHA (Dhahran Hospital in Saudi Arabia): 12; EBC (Origin Enterobacter cloacae): 1. BlaCTX-M was detected in 51 isolates. Both coexisted in one E. coli and two K. pneumoniae. In one of the K. pneumoniae isolate, all phenotypic tests employed were negative. A high degree of cross resistance to other classes of antimicrobials was observed. Carbapenem resistance was noted in 21 isolates. The concurrent occurrence of Amp C and CTX-M is not common in clinical isolates of Enterobacteriaceae. Phenotypic tests perform poorly when these enzymes are coproduced.