Functional and Safety Aspects of Enterococci Isolated from Different Spanish Foods

doi:10.1078/0723-2020-00248

Systematic and Applied Microbiology

Volume 27, Issue 1, 2004, Pages 118-130

https://doi.org/10.1078/0723-2020-00248 Get rights and content

Summary

The incidence and diversity of enterococci in retail food samples of meat, dairy and vegetable origin was investigated. Enterococci were present, at concentrations of 10¹ to 10⁴ CFU/g. Fifty selected isolates from food samples grouped in two separate clusters by RAPD analysis. Cluster G1 (72% of the isolates) contained the E. faecium CECT 410^T type strain, and also showed a high degree of genetic diversity. Cluster G2 (28% of the isolates) contained the E. faecalis CECT 481^T type strain and was genetically more homogeneous. Virulence traits (haemolysin, gelatinase or DNAse activities, or the presence of structural genes cylL, ace, asa1 and esp) were not detected. All isolates were sensitive to the antibiotics ampicillin, penicillin, gentamicin, streptomycin and chloramphenicol. A high pecentage of isolates were resistant to erythromycin and rifampicin. Many isolates showed intermediate sensitivity to several antibiotics (tetracycline, ciprofloxacin, levofloxacin, or quinupristin/dalfopristin). Vancomycin and teicoplanin resistance was detected in one strain, but vanA, vanB, vanC1, vanC2 or vanC3 genes were not detected. Many of the isolates showed functional properties of food or health relevance. Production of antimicrobial substances was detected in 17 of the isolates, and 14 of them carried structural genes for enterocins A, B and/or P.

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Enterococci are widely distributed in dairy sector. They are commensals of the gastrointestinal tract of animals, thus, via fecal contamination, could reach raw milk and dairy products. The aims of this study were: 1) to investigate the enterococcal diversity in cow feces and milk samples and 2) to evaluate the antibiotic resistance (AR) of dairy-related enterococci and their ability to transfer resistance genes.
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From a selection of seven traditional and 14 innovative alheiras, 491 lactic acid bacteria (LAB) were isolated and tested for their antimicrobial activity against several food-borne pathogens. Among these, six strains revealed antimicrobial activity through potential bacteriocin production against 14 Listeria monocytogenes strains, Enterococcus faecalis ATCC 29212, Clostridium sporogenes ESB050, and Clostridium perfringens ESB054.
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Citation Excerpt :
Dnase activity was determined using a Dnase agar medium (Pronadisa, Spain) with 0.05 g/L of methyl green (Sigma). The result was considered positive when after incubating the plates at 30 °C for 48 h, a clear halo was observed around the colonies (Ben Omar et al., 2004). All experiments were performed in duplicate, and S. aureus ATCC 25213 was used as a positive control.
The antimicrobial activity of lactic acid bacteria (LAB) isolated from traditional ripened foods against various foodborne pathogens was evaluated, and the bacteriocins produced by the selected LAB of interest were characterized. For this, 33 bacteria were initially selected for their ability to produce proteinaceous compounds with antimicrobial activity. Subsequently, only three isolates were selected since they did not have virulence factors or were resistant to antibiotics. Due to the greater bacteriocin activity spectrum, Lactilactobacillus sakei 205 was selected, and its bacteriocin was characterized. The highest activity level (6400 AU/mL) was observed against Enterococcus faecalis ATCC 29212 during the growth of Lb. sakei 205 for 18–20 h. The bacteriocin, with an approximate molecular size of 24 kDa, remained stable at temperatures ranging from 25 °C to 60 °C, at pH values between 4.0 and 6.0 and was sensitive to all the detergents and inactivated with the proteolytic enzyme proteinase K, confirming its proteinaceous nature. Furthermore, it affected the viability of all the studied pathogens and repressed their growth for at least 12 h. In this preliminary study, the identified properties of Lb. sakei 205 strain and its produced bacteriocin indicate its potential application as a biopreservative in traditional ripened foods.
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