New methods in the evaluation of chemical disinfectants used in Health Care Services

Background A considerable number of tests are recommended in the literature to evaluate in vitro commercial chemical solutions. The variety of tests reflects their limitations and the need to enhance disinfection process. Methods In this study the efficacy of 4 chemical disinfectants selected by their practical use in Health Care Services and by literature recommendation in aerobic and in strict anaerobic bacteria were evaluated by their practical use in Health Care Services and by literature recommendation in aerobic and in strict anaerobic bacteria. Viability was tested in biofilms grown on glass and rubber tip carriers. Results The results showed microbial growth in chemical solutions at concentrations recommended by the literature or at very close concentrations to them. Viable cells were recovered from biofilms after 30 minutes (Bacteroides fragilis) and 60 minutes (Streptococcus mutans and Salmonella thyphimurium) contact with 2.4% glutaraldehyde and after 60 minutes (S typhimurium) in 2.0% glutaraldehyde. In 70% ethyl alcohol, S tiphymurium was viable up to 10 minutes, Eschericia coli up to 30 minutes, and S mutans up to 60 minutes. In 1% sodium hypochlorite, S mutans was viable up to 30 minutes and S tiphymurium up to 45 minutes. Detection of cell viability could be related to methodologic differences, including biofilm formation, as demonstrated by scanning electron microscopy. It should be emphasized that B fragilis, the most clinically relevant obligate anaerobe, remained viable in one routinely used solution. Conclusion These findings pointed out the need of periodic surveillance of disinfectantsʹ activity used in Health Care Services and the need of reviewing routines of disinfection protocols.