Sodium hypochlorite is more effective than 70% ethanol against biofilms of clinical isolates of Staphylococcus aureus

Abstract

Although disinfectants are used for eradication of bacteria from environmental surfaces, their antibiofilm efficacy is often not considered in determining the choice of disinfectant. This study aimed to compare the effectiveness of 2 commonly used disinfectants, sodium hypochlorite and ethanol, against the planktonic and biofilm state of Staphylococcus aureus clinical isolates. Effect of 0.6% sodium hypochlorite and 70% ethanol was determined on the planktonic and biofilm states of 10 strong and weak biofilm formers through estimation of changes in colony forming unit counts and absorbance values. The morphologic changes were observed by scanning electron microscopy. Significant difference in the efficacy of sodium hypochlorite and ethanol was observed against the biofilm (P = .004) as well as planktonic (P = .000) states of S aureus. However, no significant difference was observed in their activity against strong and weak biofilm formers. On electron microscopy, sodium hypochlorite was found to induce significant formation of craters and irregular depressions on the surface of strong biofilm formers. Sodium hypochlorite demonstrated superior efficacy in controlling both planktonic and biofilm states of growth in S aureus. Furthermore, the characteristic morphologic changes observed in strong biofilm formers hint at its biofilm-specific activity.