Enterococcus hirae, Enterococcus faecium and Enterococcus faecalis show different sensitivities to typical biocidal agents used for disinfection

Background: Enterococcus faecium and E. faecalis are known nosocomial pathogens. The bactericidal activity of biocidal agents used for disinfection, however, is determined with E. hirae.

Aim: To find out whether E. hirae is a suitable species to evaluate the efficacy of biocidal agents against the clinically relevant species E. faecalis and E. faecium.

Methods: The bactericidal activity was determined in suspension tests according to EN 13727 using E. faecium ATCC 6057, E. faecalis ATCC 47077 and E. hirae ATCC 10541. Glutaraldehyde, ethanol, benzalkonium chloride, peracetic acid and sodium hypochlorite were used with three exposure times per biocide. When major differences in the sensitivity of the three enterococcal species to the respective substance was found, two more replicates were performed. The number of colony-forming units (cfu) was transformed into decimal logarithms. Results from replicate experiments were described with means and standard deviations.

Findings: At a 5-min exposure time, E. hirae was found to be more tolerant to 0.2% glutaraldehyde and 0.0125% peracetic acid compared to E. faecium and E. faecalis, whereas it was more susceptible to 40% ethanol and 3% sodium hypochlorite. Only with 0.00125% benzalkoniumchloride (15 min) was the susceptibility of E. hirae between that of E. faecium and E. faecalis.

Conclusions: E. hirae is a suitable species when a bactericidal activity should be determined against enterococci with glutaraldehyde and peracetic acid. E. hirae may not be a suitable species for ethanol or sodium hypochlorite if the bactericidal activity should include the clinical pathogens E. faecium and E. faecalis.