Reduced Susceptibility to Biocides among Enterococci from Clinical and Non-Clinical Sources

Abstract

Background Wide use of biocidal agents such as benzalkonium chloride (BCC) and chlorhexidine digluconate (CHX) in hospitals and non-hospital environments, has raised concerns over the emergence of non-susceptible strains. Efflux pumps are of known main mechanisms in biocide tolerance which have been rarely addressed in enterococci - members of gut microbiota which can cause serious problems particularly in hospitalized patients. The purpose of this study was to investigate the susceptibility of enterococci from different sources (clinical and fecal isolates) toward BCC and CHX, and its correlation with efflux associated genes. Also, possible link between biocide tolerance and antibiotic resistance was examined. Materials and Methods One hundred and four enterococcus isolates including clinical (n = 54) and fecal isolates (n = 50) were studied for susceptibility toward BCC, CHX, ciprofloxacin, gentamicin and vancomycin. Twelve efflux associated genes were investigated by polymerase chain reaction assay. Results In clinical isolates, reduced susceptibility to CHX and resistance to gentamicin and ciprofloxacin were significantly higher than fecal isolates. Vancomycin resistance was associated with increasing minimum inhibitory concentration of CHX. Among all investigated genes, only three ones, efr A, efr B and eme A were detected which were significantly associated with reduced susceptibility to CHX and were more frequent among clinical isolates. Also, high level resistance to gentamicin was significantly associated with the presence of efr A/B as well as with reduced susceptibility to CHX. Conclusion As expected, reduced susceptibility to CHX, was significantly higher in clinical isolates. However, the presence of a vancomycin-resistant enterococci among fecal isolates of healthy people which showed resistance/tolerance to studied antimicrobial agents, was unexpected and highlights the need to investigate other non-hospital environments to avoid dissemination of antimicrobial resistance. Correlation between reduced susceptibility to CHX and high level resistance to gentamicin, substantiates monitoring of biocide tolerance particularly in the healthcare settings to control the establishment of antimicrobial resistant strains.

Unraveling Enterococcus susceptibility to quaternary ammonium compounds: genes, phenotypes, and the impact of environmental conditions

“…Despite the increased use of QACs in recent years ( 4 , 5 ), E. faecalis and E. faecium from various epidemiological backgrounds remain susceptible to QACs concentrations lower than those recommended for disinfection or preservation, with MIC and MBC distributions for BC and DDAC being consistent with previous reports ( 10 , 20 , 22 , 27 , 43 ). The observed similar QACs phenotypes in isolates with and without qacZ gene, along with supporting published data ( 20 , 22 ), suggest that QACs tolerance genes may not have a significant impact on the survival of Enterococcus spp.…”

“…The apparent lack of selective advantage conferred by QACs tolerance genes in Enterococcus seems to be also corroborated by their low prevalence among Enterococcus isolates, which could be explained by rare horizontal transfer events, lack of stability of the acquired genes or genetic contexts due to, for example, high fitness costs ( 11 ). Accordingly, literature mostly supports that Enterococcus from diverse sources do not seem to be relevant reservoirs of known QACs tolerance genes ( 20 – 22 , 43 ), with few exceptions ( 24 , 25 ). In addition, we found that pre-exposure to BC did not induce a higher tolerance to this biocide in isolates carrying qacZ , which may indicate that the BC concentration and exposure times tested were not able to induce the gene expression of the efflux pump encoded by qacZ , that increased expression levels of qacZ did not lead to a detectable increase in Enterococcus tolerance to BC, or that other gene expression regulatory systems or environmental inductors are needed.…”

Evaluating the effectiveness of Chlorhexidine on Gram-positive and Gram-negative bacteria in Iran: a systematic review

“…One of the 15 full-text examined papers had a sample size of fewer than 10 isolates and also, two studies were performed just on non-clinical isolates so, did not meet our inclusion criterion. Finally, 12 papers met the inclusion criteria and were submitted to our evaluation (1,(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). A owchart of the literature search, the selection procedures and reasons for exclusion are presented in Figure 1.…”

Current insights into the effects of cationic biocides exposure on Enterococcus spp.

“…Similarly, other authors have found significant differences across their Enterococcus spp. collections (Schwaiger et al, 2014;Duarte et al, 2019;Sobhanipoor et al, 2021;Kheljan et al, 2022;Pereira et al, 2022Pereira et al, , 2023. Most found a higher occurrence of strains with decreased susceptibility to CHX, DDAC, or BC among clinical isolates comparing to Enterococcus from other origins included in the same study (Schwaiger et al, 2014;Guzman Prieto et al, 2017;Duarte et al, 2019;Sobhanipoor et al, 2021;Pereira et al, 2023), although contradictory data has also been reported for BC (Sobhanipoor et al, 2021;Kheljan et al, 2022).…”