Multidrug-resistant Pseudomonas aeruginosa strains harbouring R-plasmids and AmpC beta-lactamases isolated from hospitalised burn patients in a tertiary care hospital of North India.

The present study was designed to determine resistance rates and patterns in Pseudomonas aeruginosa isolates obtained from hospitalised burn patients in an Indian tertiary care hospital. To that end, we isolated plasmid(s) from the multidrug-resistant isolates, demonstrated the plasmid-mediated resistance by curing and transformation experiments, and screened all the isolates for the occurrence of AmpC beta-lactamases. Thirty isolates of P. aeruginosa were analysed for the presence of antibiotic resistance. Plasmid-curing experiments and AmpC beta-lactamase detection were performed on all the isolates and seven isolates showing the most common antibiotic resistance pattern were selected for plasmid isolation and transformation experiments. All 30 isolates were multidrug-resistant and the majority (83.3%) of isolates were resistant to seven or more antibiotics, out of 11 antibiotics tested including anti-pseudomonal and non-anti-pseudomonal antimicrobial drugs. The most striking feature was the presence of resistance to amikacin. A 48.5-kb plasmid was isolated from the isolates. Curing and transformation experiments showed that resistance to amikacin was plasmid-mediated. Phenotypic screening for the occurrence of AmpC beta-lactamases showed that 20% of isolates were AmpC producers whereas 10% of isolates were characterised as 'indeterminate' for AmpC enzyme. In conclusion, a markedly high (56.7%) resistance to amikacin was noted in the present study. Amikacin resistance was determined to be plasmid-encoded and the presence of an AmpC beta-lactamase was inferred in 20% of isolates. This is among the first reports regarding the emergence of plasmid-mediated resistance to amikacin and the occurrence of AmpC beta-lactamases in P. aeruginosa strains from India.