Biocide and Copper Tolerance in Enterococci from Different Sources

Abstract

Antimicrobial resistance in enterococci is a matter of concern. A collection of 272 strains (including 107 Enterococcus faecalis and 165 Enterococcus faecium strains) isolated from meat and dairy products, seafood, vegetable foods, wildflowers, animal feces (ewe, goat, horse, mule), and hospitals were tested for sensitivity to biocides of different classes (quaternary ammonium compounds, a bisphenol, and a biguanide) and copper sulfate. Most isolates were inhibited at 25 mg of benzalkonium chloride or cetrimide per liter or at 2.5 mg of hexadecylpyridinium chloride per liter. Few isolates had MICs higher than 25 mg/liter for benzalkonium chloride (2.2%), cetrimide (0.74%), or hexadecylpyridinium chloride (0.37%), although they were all inhibited at 250 mg/liter. The population response to triclosan was very homogeneous, and most isolates (98.16%) were inhibited at 250 mg of triclosan per liter. Chlorhexidine showed the greatest variability, with MICs in a range from 2.5 to 2,500 mg/liter. Remarkably, 74.57% of isolates from clinical samples required 2,500 mg of chlorhexidine per liter for inhibition, compared to much-lower concentrations required for most isolates from other sources. Enterococci were inhibited by copper sulfate in a concentration range from 4 to 16 mM, with no bimodal distribution. However, most isolates required 12 mM (41.91%) or 16 mM (47.43%) for inhibition. The highest percentages of isolates requiring 16 mM CuSO4 were from vegetable foods, seafood, and wildflowers. The results from the present study suggest intermediate levels of copper tolerance and a low incidence of biocide tolerance in the enterococci investigated, except for chlorhexidine in clinical isolates.

Differential Effects of Chlorhexidine Skin Cleansing Methods on Residual Chlorhexidine Skin Concentrations and Bacterial Recovery

“…Notably, some strains of bacteria have been reported to have CHG MICs as high as 2500 µg/mL. 22 In our study, cleansing with no-rinse 2% CHG-impregnated cloth was the only method that achieved CHG concentrations as high as 2500 µg/mL.…”

Microscopic and Spectroscopic Analyses of Chlorhexidine Tolerance in Delftia acidovorans Biofilms

“…In a recent study (47), CHX exhibited the greatest variability when 272 Enterococcus strains were tested for sensitivity to biocides of different classes (quaternary ammonium compounds, a bisphenol, a biguanide, and copper sulfate), with MICs ranging from 2.5 to 2,500 mg ml Ϫ1 . Similarly, the MICs of CHX for 52 strains of subgingival plaque (biofilm) bacteria ranged from 8 to 500 g ml Ϫ1 (48), whereas for methicillin-resistant Staphylococcus aureus isolates collected over 15 years, the MIC range was found to be 0.5 to 16 g ml Ϫ1 (49).…”

Efficacy of Triclosan as an Antimicrobial Hand Soap and Its Potential Impact on Antimicrobial Resistance: A Focused Review

“…Resistance to Enterococcus faecalis occurs primarily through genetic changes to fabI and efflux pumps, and resistance to Enterococcus faecium occurs through mutations to fabI . One study evaluated 272 Enterococcus strains from a variety of sources and found almost no decreased susceptibility to triclosan . Another study evaluated vancomycin‐resistant E. faecium isolates from a wastewater treatment plant in Texas and found that 66% of isolates had MICs above the concentration expected to be obtained by using 0.1% triclosan hand soap (2.1 μg/ml) .…”

“…One study evaluated 272 Enterococcus strains from a variety of sources and found almost no decreased susceptibility to triclosan. 57 Another study evaluated vancomycin-resistant E. faecium isolates from a wastewater treatment plant in Texas and found that 66% of isolates had MICs above the concentration expected to be obtained by using 0.1% triclosan hand soap (2.1 lg/ml). 58 However, a link between triclosan resistance and antimicrobial resistance was not seen.…”