Susceptibility of selected strains used for evaluation of biocidal efficiency of disinfectants and antibiotic-resistant strains to didecyldimethylammonium chloride in 2-propanol.

Introduction: Didecyldimethylammonium chloride is an active substance which is part of variety of formulations used for the disinfection and antisepsis, both in the medical area as well as in the food, industrial and institutional area. Because of the widespread use of this substance and the development of bacterial resistance to quaternary ammonium compounds (QACs), the aim of this study was determination of the susceptibility of the standard strains used for the evaluation of the effectiveness of disinfectants and standard antibiotic-resistant strains to didecyldimethylammonium chloride in 2-propanol and its bactericidal activity.

Methods: Susceptibility of standard strains used for the evaluation of the effectiveness of disinfectants (Staphylococcus aureus ATCC 6538-SA; Pseudomonas aeruginosa ATCC 15442-PA) and standard antibiotic-resistant strains (Staphylococcus aureus ATCC 43300-MRSA; Pseudomonas aeruginosa ATCC 47085-PAO-LAC) to CMAP was determined by minimum inhibitory concentrations (MICs) and minimum bactericidal concentration (MBCs). The bactericidal efficiency of CMAP against these strains was evaluated by using phenol coefficient (PC).

Results: Susceptibility of Gram-positive tested strains SA and MRSA to CMAP was similar (P>0,05). Significant difference in susceptibility of tested Gram-negative strains to CMAP was evaluated between PA and PAO-LAC strains (P<0,05). However,.higher resistance of PAO-LAC to CMAP was not significant when parameters such as concentration and contact time were applied in PC method.

Conclusions: The correct determination and application of "in use" parameters (i.e. concentration, contact time, temperature and interfering substances) in disinfection process prevents the spread of resistant strains in.the environment.