Resistance due to aminoglycoside modifying enzymes in Pseudomonas aeruginosa isolates from burns patients.

BACKGROUND & OBJECTIVE: Enzymatic modifications of aminoglycosides result in high-level resistance in numerous bacterial species. However, the data on this aspect are elementary in our country. The present study was therefore designed to determine resistance rates and patterns, and to find out the prevalent aminoglycoside modifying enzymes (AMEs) in clinical isolates of Pseudomonas aeruginosa from hospitalized burn patients. METHODS: Forty two, non-repeat, clinical isolates of P. aeruginosa obtained during a period from February to July 2003, were analysed for the presence of antibiotics resistance. On the basis of aminoglycoside susceptibility patterns, resistance phenotypes and possible AMEs were inferred according to interpretative reading. Seven isolates collected during the same period and previously characterized to harbour a 48.5 kb plasmid, encoding multiple drug resistance, were also analysed for aminoglycoside susceptibility patterns, and AMEs encoded by the plasmid were inferred. RESULTS: Ninety six per cent of the isolates were multi drug-resistant and majority (71.4%) were resistant to 5 or more antibiotics. Markedly high resistance to tobramycin (83.6%) and amikacin (55.1%) was noted, whereas gentamicin resistance was present in 32.6 per cent isolates. The enzyme N-acetyl transferases (AAC) viz. AAC(6')-I was the most common isolated AME followed by AAC(3)-II in 42.8 and 20.4 per cent of isolates respectively. The plasmid harbouring isolates belonged to AAC(6') phenotype and the enzyme encoded was inferred to be AAC(6')-I. INTERPRETATION & CONCLUSION: Markedly high resistance to tobramycin and amikacin was noted in the present study. AAC(6')-I was the most common AME and was inferred to be plasmid encoded in R-plasmid harbouring isolates. This is among the premier reports regarding the aminoglycoside resistance due to AMEs especially plasmid encoded, in P. aeruginosa from India. Further studies are required from different parts of the country to findout the prevalence of aminoglycoside resistance due to AMEs in P. aeroginosa isolates.