RÉSUMÉ
Context: In Pseudomonas aeruginosa, AmpC β-lactamases are often responsible for high-level resistance to β-lactam antibiotics. The co-production of plasmid-mediated AmpC along with chromosomal Pseudomonas-derived cephalosporinases thus remain a serious clinical concern owing to high resistance spectrum towards antibiotics. Aim: The present study was performed to investigate the co-existence of both chromosomally-encoded and plasmid-mediated AmpC β-lactamase among clinical isolates of P. aeruginosa. Setting and Design: It is a cross-sectional study carried out in the Department of Microbiology in a tertiary referral hospital of northern India. Methods and Methods: A total of 329 consecutive, non-duplicate clinical isolates of P. aeruginosa, were selected for the detection of AmpC β-lactamases and confirmed for AmpC production by modified three dimensional (M3D) test. Ceftazidime -imipenem antagonism test was used to detect inducible AmpC producers. Molecular characterisation of chromosomally-encoded blaPDC and plasmid-mediated AmpC gene was studied by performing polymerase chain reaction (PCR). Result: A total of 214 (65%) isolates were confirmed for AmpC production by M3D test. On performing multiplex PCR, 27 isolates were detected posessing blaCMY type of plasmid-mediated AmpC gene. While 48 isolates were found to harbour chromosomally-encoded blaPDC gene co-production of both chromosomal and plasmid-encoded AmpC was reported in eleven isolates. Conclusions: Although these chromosomally-encoded cephalosporinases might spread more slowly than mobilised AmpC, but it is likely that in the present scenario of intense antibiotic pressure, this will become an increasing problem and may further limit our antibiotic choices.