Effect of adaptation process of Pseudomonas aeruginosa to didecyldimethylammonium chloride in 2-propanol on bactericidal efficiency of this active substance.

BACKGROUND Microorganisms are characterized by two types of resistance innate and acquired. Innate resistance is associated with the construction of the surface structures. Wide use of active substances as antimicrobial compounds, especially in inhibitory concentrations, may promote the acquisition of bacterial resistance to these substances in the process of adaptation. OBJECTIVE The aim of the study was to determine changes in efficiency of didecyldimethylammonium chloride in 2-propanol (CMAP) against the Pseudomonas aeruginosa strains, which were adapted to this active substance. MATERIALS AND METHODS Adaptation studies were conducted using two strains: P. aeruginosa ATCC 15442 (PA), which is used in estimation of biocide efficiency and tetracycline-resistant P. aeruginosa ATCC 47085 (PAO-LAC) strain. These strains were adapted to the active substance Bardac22: 50% v/v didecyldimethylammonium chloride in 20% v/v 2-propanol (CMAP) according to the National Institute of Hygiene procedure. After adaptation, obtained isolates were classified to three groups and passaged to solid media: A - strains unadapted passaged onto slant medium without active substance, control group; B - strains with adaptive resistance passaged onto slant medium with 375 mg/l CMAP; C - strains with adaptive resistance passaged onto slant medium without CMAP. Changes in susceptibility of examined strains were determined on the basis of minimum inhibitory concentrations (MICs) by broth dilution method. The minimum bactericidal concentrations (MBCs) were determined by subculture P. aeruginosa strains on solid media without CMAP. The efficiency of CMAP against isolates obtained after adaptation processes was evaluated by using phenol coefficient (PC). RESULTS There were no differences in the adaptation process between two strains of P. aeruginosa: PA and PAO-LAC. Both isolates obtained after the adaptation process was characterized by approximately 6-8 fold higher MICs compared to the MICs of these strains before the adaptation. Strains passaged to a solid media characterized a variable sensitivity to CMAP. As compared to a control group A, the isolates of PA and PAO-LAC from group B and isolate PA from group C exhibited the highest and stable insensitivity (MIC from > 700 to >1000 mg/l) to 48-49 passages. Isolates from group C of PAO-LAC maintained insusceptibility up to 20th passage (MIC >375 mg/l). There were no statistically significant changes in the CMAP bactericidal efficacy against isolates of reduced sensitivity. CONCLUSIONS Adaptation of P. aeruginosa strains to didecyldimethylammonium chloride in 2-propanol does not significantly change bactericidal efficacy of this active substance against isolates with reduced sensitivity. Antibiotic-resistant strain PAO-LAC showed a similar adaptability and a similar sensitivity to the CMAP as a strain PA used to assess the effectiveness of disinfectants. KEY WORDS adaptation process, Pseudomonas aeruginosa, quaternary ammonium compounds, bactericidal efficiency.