Rethink on recommended concentrations of disinfectants in the light of biofilm, based on in vitrostudy

Abstract

Background: Some medical devices are reused after treatment with disinfectants at manufacturer's recommended concentrations (RCs), based on experimental evaluation studies of their bactericidal, sporicidal, and mycobactericidal concentrations. However, this may not be sufficient to eliminate all colonized highly drug-resistant biofilms on medical devices, resulting possibility in iatrogenic infections by recolonization of highly resistant persisters. The objective of this study is to evaluate the antibacterial efficacy of different concentrations of novel and conventional disinfectants on in vitro grown biofilm of multidrug-resistant nosocomial bacterial isolates and a reference strain. Materials and Methods: Multidrug-resistant and strong biofilm producers Pseudomonas aeruginosa (n = 4) and Escherichia coli (n = 5) nosocomial isolates and one reference strain, P. aeruginosa PAO-1, were selected after testing their biofilm status by modified Christensen's method and Stepanovic's interpretative criteria. The activity of three different groups of new disinfectants, Novacide, Virkon, Silvicide and two conventional disinfectants, phenol and glutaraldehyde, were assessed on their in vitro grown biofilms as percentage of total surviving bacteria within biofilm matrix after challenge at different concentrations in terms of multiples of RC and different contact time. Results: Modified RCs for Virkon, phenol, and Silvicide, as pointed out by in vitro study, were 4, 8, and 10 times higher than the one suggested by the manufacturer. Novacide was least effective, whereas glutaraldehyde at its available concentration was also not effective in removal of biofilm bioburden. Conclusions: RC was not sufficient to eliminate the in vitro biofilms tested in this study. Further studies using medical devices materials should be performed for clarification. However, this study points out possible relevant limitations of currently used hospital disinfectants and concentrations against biofilms. Additional measures to prevent reinfections related to their use of medical devices are mandatory, and this study suggests that optimization of disinfectants concentrations may be highly relevant.