Biofilm formation abilities and disinfectant-resistance of Pseudomonas aeruginosa isolated from cockroaches captured in hospitals

Abstract

Forty-five strains of Pseudomonas aeruginosa isolated from cockroaches captured in hospitals were investigated with regard to their biofilm-forming ability and resistance to various disinfectants in various cellular states. The hydrophobicity value varied among the test strains from 0.001 to 0.241, and the mean±standard deviation (SD) was 0.101±0.074. The relative viscosity of the extracellular product was measured. All test strains produced a mucous substance, and the value was 1.05-1.30 (mean±SD: 1.11±0.06), showing that all test strains had a biofilm-forming ability. Bactericidal experiments were performed using 6 disinfectants: ethanol, Hibitane, Isojin, Osvan, Tego 51, and Welpas. When bacteria in suspension were exposed to the disinfectants for 1 min (suspension test), 5 of the 6 disinfectants excluding Tego 51 completely killed all test strains, showing high bactericidal effects. In contrast, when adherent bacteria were exposed to the disinfectants for 1 min (adhesion test), the killing rate by Welpas was 100 %, but those by Isojin and ethanol were lower (88.9 and 60.0 %, respectively), that by Osvan was only 4.4 %, and no bacteria were killed by Hibitane or Tego 51. These findings showed that the bactericidal effects markedly decreased in the case of adherent P. aeruginosa.