Evaluation of bactericidal efficacy of a new chlorine-based disinfectant cleaner for sericulture against Enterococcus species by European Norm method

Abstract

 The genus Enterococcus, a group of gram-positive bacteria, currently comprises 62 described species. In sericulture, some enterococci are serious pathogens causing the gastrointestinal disease “flacherie” in silkworm larvae reared on artificial diets. In the present study, the author evaluated the bactericidal efficacy of a new chlorine-based disinfectant cleaner for sericulture (DCS) consisting of NaOCl, 0.5% Na₂CO₃ and 0.2% Na₆P₄O₁₃. By varying the concentrations of free available chlorine (FAC) in the DCS from 256 to 1,024 mg/L, each bacterial suspension of four Enterococcus species (E. faecalis, E. faecium, E. hirae and E. mundtii) was tested with the DCS (20°C) under clean or low soiling conditions according to the European Norm 1656 method used for industrial purposes. The test results showed that the DCS with FAC 256 mg/L under the clean condition (0.03% BSA) disinfected all Enterococcus species in 1 min with a viable bacterial count log reduction value (VBC-LRV) of >6. In contrast, under the low soiling condition (0.3% BSA), more than FAC 768 mg/L was required in the DCS to disinfect all enterococci tested in 3 min to achieve a VBC-LRV of >5. In this study, E. faecalis was found to be susceptible to DCS. In contrast, E. hirae and E. mundtii were more tolerant to DCS than E. faecium. This result suggests that the susceptibility of Enterococcus to some disinfectants may differ between species and should be considered when evaluating the bactericidal efficacy of disinfectants against Enterococcus species in future research.