ABSTRACT
BACKGROUND & OBJECTIVES: AmpC beta-lactamases are Group I cephalosporinases that confer resistance to a wide variety of beta-lactam drugs. Plasmid mediated AmpC beta-lactamases has been discovered most frequently in isolates of Klebsiella pneumoniae, K. oxytoca, Salmonella, Proteus mirabilis and Escherichia coli. The present study was undertaken to study the occurrence of multidrug resistant and AmpC beta-lactamase producing Klebsiella spp. and Escherichia coli in children less than five years of age as this age group is very susceptible to intestinal and extraintestinal infections. METHODS: A total of 116 isolates of Klebsiella species and 32 isolates of Esch. coli were tested for resistance to cephamycin such as cefoxitin, third generation cephalosporin (3GC) antibiotics (ceftazidime, cefotaxime, ceftriaxone), ampicillin, amikacin, cephaloridine, cefuroxime, co-trimoxazole, gentamycin, imipenem and tetracycline by disc diffusion method. Isolates found resistant to cefoxitin were tested for the production of AmpC beta-lactamases by three dimensional extract method. Transconjugation experiments were done to study the transfer of drug resistance and AmpC beta lactamase production from AmpC producing Klebsiella and Esch. coli isolates to a recipient Esch. coli strain (K12 J62-2). RESULTS: Twenty eight isolates (24.1%) of Klebsiella spp. and 12 (37.5%) of Esch. coli were found to be AmpC beta-lactamase producers; 66.6 per cent and 81 per cent of Klebsiella and Esch. coli isolates respectively showed resistance to all the 3GCs. All the strains were found to be sensitive to imipenem. Eighty four (72%) of Klebsiella isolates and 20 (62.5%) of Esch. coli were found to be resistant to cefoxitin. Transfer of cefoxitin resistance to the recipient strain was observed in all the AmpC producing strains of Klebsiella spp. Of the 12 AmpC producing strains of Esch. coli, only 4 (33.3%) showed the transfer of cefoxitin resistance to the recipient strain. INTERPRETATION & CONCLUSION: This study has shown the occurrence of AmpC beta-lactamase producing Klebsiella and Esch. coli strains in children in Chennai. Since AmpC beta-lactamase production is frequently accompanied by multiresistance to antibiotics, therapeutic options become limited resulting a need for new measures for the management of Klebsiella and Esch. coli infections. Also failure to identify AmpC beta-lactamase producers may lead to inappropriate antimicrobial treatment and may result in increased mortality. Detecting plasmid mediated AmpC beta-lactamase producing strains is technically difficult and the phenotypic tests for AmpC detection are not well defined. If an investigational AmpC beta-lactamase inhibitor was made available for diagnostic testing, it could be useful in combination with a suitable cephamycin to confirm AmpC production.