Effects of Benzalkonium Chloride on Planktonic Growth and Biofilm Formation by Animal Bacterial Pathogens

BACKGROUND: Resistance toward quaternary ammonium compounds (QACs) is widespread among a diverse range of microorganisms and is facilitated by several mechanisms such as biofilm formation. OBJECTIVES: In this study, the effects of benzalkonium chloride on planktonic growth and biofilm formation by some field isolates of animal bacterial pathogens were investigated. MATERIALS AND METHODS: Forty clinical isolates of Escherichia coli, Salmonella serotypes, Staphylococcus aureus and Streptococcus agalactiae (10 isolates of each) were examined for effects of benzalkonium chloride on biofilm formation and planktonic growth using microtiter plates. For all the examined strains in the presence of benzalkonium chloride, biofilm development and planktonic growth were affected at the same concentrations of disinfectant. RESULTS: The means of strains growth increase after the minimal inhibitory concentration (MIC) were significant in all the bacteria (except for E. coli in 1/32 and S. agalactiae in of 1/8 MIC). Biofilm formation increased with decrease of antiseptics concentration; a significant increase was found in all the samples. The most turbidity related to S. aureus and the least to Salmonella. CONCLUSIONS: Bacterial resistance against quaternary ammonium compounds is increasing which can increase the bacterial biofilm formation.