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A collection of 55 enterococci (41 Enterococcus faecium and 14 E. faecalis strains) isolated from various traditional fermented foodstuffs of both animal and vegetable origins, and water was evaluated for resistance against 15 antibiotics. Lower incidence of resistance was observed with gentamicin, ampicillin, penicillin and teicoplanin. However, a high incidence of antibiotic resistance was detected for rifampicin (12 out of 14 of isolates), ciprofloxacin (9/14), and quinupristin/dalfopristin (8/14) in E. faecalis strains. Enterococcus faecium isolates were resistant to rifampicin (25/41), ciprofloxacin (23/41), erythromycin (18/41), levofloxacin (16/41), and nitrofurantoin (15/41). One Enterococcus faecalis and two E. faecium strains were resistant to vancomycin (MIC>16 μg/mL). Among 55 isolates, 27 (19 E. faecium and eight E. faecalis) were resistant to at least three antibiotics. High level of multidrug resistance to clinically important antibiotics was detected in E. faecalis strains (57% of E. faecalis versus 46% of E. faecium), which showed resistance to six to seven antibiotics, especially those isolated from foods of animal origin. So, it is necessary to re-evaluate the use of therapeutic antibiotics in stock farms at both regional and international levels due to the high number of multiple resistant (MR) bacteria. Fifty-six MR E. faecalis and E. faecium strains selected from this and previous studies (Valenzuela et al., 2008, 2010) were screened by polymerase chain reaction for antibiotic resistance genes, revealing the presence of tet(L), tet(M), ermB, cat, efrA, efrB, mphA, or msrA/B genes. The ABC Multidrug Efflux Pump EfrAB was detected in 96% of E. faecalis strains and also in 13% of E. faecium strains; this is the first report describing EfrAB in this enterococcal species. The efflux pump-associated msrA/B gene was detected in 66.66% of E. faecium strains, but not in E. faecalis strains.

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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.

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