Isolation, identification of pseudomonas aeruginosa from a dental unit water line and effect of disinfectants on its antibiotic susceptibility

Abstract

Many clinical isolates are pathogenic strains that can be transmitted from one individual to another if health safety measures are not followed. Resistance of pathogenic bacteria to some antibiotics can be acquired due to use of sub-MIC levels of disinfectants. In this study, we isolated a pseudomonas sp. strain from biofilm lining the suction tube of a dental unit in a public hospital. The isolation medium was pseudomonas-base agar and the total count was 3 CFU/ ml. The isolated strain was gram negative and when examined according to API 20 NE tests was identified to be pseudomonas aeruginosa. The MIC of the disinfectant "Nanofix" to p. aeruginosa was determined. The antimicrobial susceptibility of this strain was tested before and after the disinfectant “Nanofix” treatment against 7 antibiotics namely; ciprofloxacin, tazobactam, aztreonam, meropenem, clavulanic acid, ceftizidime and vancomycin by agar diffusion method. Before disinfectant treatment the p. aeruginosa isolate showed resistance towards meropenem and ceftizidime while it showed a weak susceptibility to tazobactam and aztreonam showing inhibition zones of 1.2 cm and 1.2 cm. A moderate susceptibility to vancomycin with an inhibition zone of 1.5 cm and the strongest susceptibility was towards ciprofloxacin and clavulanic acid giving inhibition zones of 2.6, 2.2 cm respectively. After sub-MIC nanofix treatment the p. aeruginosa isolate showed no inhibition zones against tested antibiotics except for ciprofloxacin 1.8 cm and clavulanic acid 1.2 cm indicating induced resistance.