– Ethanol and other alcohols such as iso-propanol or n-propanol are typically used for hand disinfection or surface disinfection. An ethanol concentration of 40% will not be found in alcohol-based hand rubs because the bactericidal efficacy will be too low to fulfill European efficacy standards such as EN 1500. Even hand rubs based on 60% or 70% often fail to meet the EN 1500 efficacy requirements although the alcohols are effective against E. faecium and E. faecalis [11, 14, 15, 16]. In that respect it is of concern that the use of E. hirae may yield a sufficient efficacy against enterococci although E. faecium and E. faecalis are less susceptible.

Nosocomial infections or hospital-acquired infections (HAIs) are a major patient safety issue in hospitals.

The most frequent nosocomial infections are pneumonia (usually ventilator-associated), urinary tract infection (usually catheter-associated) and primary bloodstream infection (usually associated with the use of an intravascular device) [1]. Virtually every pathogen has the potential to cause infection in patients but only a limited number of bacterial species is responsible for the majority of HAIs. Among them Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and enterococci are the most common [2]. Enterococci account for about 10% of hospital-acquired bacteremia cases and are a major cause of sepsis worldwide [3]. HAIs caused by enterococci are difficult to treat due to acquired resistance to many classes of antibiotics [4]. Considering the severity of the consequences of nosocomial infections, such as morbidity, mortality, prolonged stay, costs, and treatment problems, it is all the more important that preventive measures in hospitals and other health facilities are fully effective [5]. Targeted disinfection, with species that are considered to be the most resistant representatives of a whole range of human pathogenic microorganisms and, due to their role in nosocomial infections, also include enterococci. As part of the standardization efforts to determine the efficacy of disinfectants at European level, the enterococcal strain Enterococcus (E.) faecium, formerly used for chemical and chemo-thermal disinfection processes, was replaced by E. hirae. E. faecium is currently only used for testing thermal disinfection processes, such as for instance for testing laundry disinfection processes at temperatures above 60 °C [6]. The differences in heat tolerance between the enterococcal species is already well described resulting in the use of E.hirae for testing chemical disinfectants and E. faecium for chemo-thermal and thermal processes [7, 8]. Pidot et al. have shown in 2018 that some multidrug-resistant E. faecium isolates isolated recently are more tolerant to 23% iso-propanol than older isolates suggesting an adaptive cellular response [9]. Overall, the chemical susceptibility of two common clinical species (E. faecalis and E. faecium) and the commonly used test species (E. hirae) has not yet been sufficiently investigated [10, 11, 12]. The aim of this study was therefore 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. Therefore, we determined the in vitro bactericidal efficacy of five substances from commonly used groups of biocidal agents (aldehydes, alcohols, surfactants, oxidizing agents and halogens) on E. hirae, E. faecium and E. faecalis according to the European Norm EN 13727 [13].effective procedures and correctly performed, is one of the most important measures to interrupt the transmission of pathogens in hospitals. In Europe, the microbicidal effectivity of any disinfection procedure must be evaluated and confirmed in accordance with national or international standards and norms in vitro and under practical conditions before it can be used in hospitals [6]. These efficacy tests are performed with defined test

Our data show that the testing of disinfectants based upon a culture collection E. hirae strain alone may not represent the sensitivity of other collection Enterococcus spp. with more clinical relevance. At a 5 min exposure time the current EN 13727 test species 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) the susceptibility of E. hirae was between E. faecium and E. faecalis. Based on these data E. hirae is a suitable species when bactericidal activity needs to be determined against enterococci with the biocidal agents glutaraldehyde and peracetic acid. It may, however, not be a suitable species for ethanol at 40% or sodium hypochlorite at 3% if the bactericidal activity shall include the clinical pathogens E. faecium and E. faecalis.

Ethanol and other alcohols such as iso-propanol or n-propanol are typically used for hand disinfection or surface disinfection. An ethanol concentration of 40% will not be found in alcohol-based hand rubs because the bactericidal efficacy will be too low to fulfill European efficacy standards such as EN 1500. Even hand rubs based on 60% or 70% often fail to meet the EN 1500 efficacy requirements although the alcohols are effective against E. faecium and E. faecalis [11, 14, 15, 16]. In that respect it is of concern that the use of E. hirae may yield a sufficient efficacy against enterococci although E. faecium and E. faecalis are less susceptible.

The situation is different in surface disinfection. Many low alcohol products are available for immediate use in the patient environment, often as presoaked tissues [17]. Low alcohol concentration has the advantage of a better compatibility with plastic surfaces which are now commonly found in healthcare such as mobile phones or tablet computers [18]. Based on our data obtained with suspension tests it seems to be possible that low alcohol surface disinfectants which are effective against E. hirae do not provide the same level of bacterial killing against E. faecium or E. faecalis. In 2014 a dramatic increase of infections caused by vancomycin-resistant enterococci has been described [19]. The reasons for the increase are still unknown. But it is known that Enterococcus spp. can survive on inanimate surfaces between 4 days and 4 months [20]. It is therefore important to ensure a sufficient bactericidal efficacy of alcohol-based surface disinfectant against Enterococcus spp. However even with higher concentrations of alcohol it is essential to apply a sufficient volume. Approximately 10% of the solution is released during wiping when a soaked tissue is used [16, 21]. It has been shown previously that the application of a low volume of an effective alcohol results in failure to meet the efficacy requirements [16].

Sodium hypochlorite at 3% was also more effective in 5 min against E. hirae and less effective against E. faecalis and E. faecium. It is a biocidal agent commonly used in many countries for surface disinfection [22]. Our findings with E. faecalis appear plausible because sodium hypochlorite at 2.5% has been described to achieve at least 5 log10 against ATCC 35550 (10 min) and ATCC 29212 (20 min) [23, 24]. The very low effect of 3% sodium hypochlorite even in 15 min against E. faecium is of concern and should be followed up with more research on the possible implications for its use in healthcare.

In this study we have only used culture collection strains from each of the three Enterococcus spp. in order to compare the susceptibility of potential test strains for disinfectant efficacy testing. We have not used any Enterococcus spp. clinical isolates. That is why we cannot evaluate whether the different biocidal agents would reveal a similar bactericidal activity against clinical isolates of each of the three Enterococcus species.

Another limitation of our study is that all experiments were carried out using a low organic load described as clean conditions. That is why we are unable to describe if similar or other results would be obtained under dirty conditions. Clean conditions were chosen because they reflect the majority of applications of these agents. Alcohol-based hand rubs are applied to clean hands, ethanol is a typical biocidal agent used for hand disinfection. Instrument disinfectant should be used on cleaned instruments, glutaraldehyde, benzalkonium chloride and peracetic acid are typical agents used for instrument disinfection. Surface disinfection is often performed without prior cleaning, benzalkonium chloride and sodium hypochlorite are typical agents used for surface disinfection. With sodium hypochlorite it has been described before that the bactericidal efficacy will be impaired in the presence of organic load [25].

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 at 40% or sodium hypochlorite at 3% if the bactericidal activity shall include the clinical pathogens E. faecium and E. faecalis.

By Miranda Suchomel, Anita Lenhardt, Günter Kampf, Andrea Grisold

https://www.journalofhospitalinfection.com
https://www.journalofhospitalinfection.com/article/S0195-6701(19)30345-7/fulltext

For references: https://www.journalofhospitalinfection.com/article/S0195-6701(19)30345-7/references