Biopreservation potential ofEnterococcus faecalisisolated from Italian traditional raw milk cheeses

Does Enterococcus faecalis from Traditional Raw Milk Cheeses Serve as a Reservoir of Antibiotic Resistance and Pathogenic Traits?

Enterococcus faecalis is not only a prevalent species among dairy microbial community but also a well-documented opportunistic pathogen. Food safety should exclude the possibility of consumer exposure to its virulence traits through consumption of dairy products. In this study, an integrated approach based on both phenotypic and genotypic methods was applied to investigate the incidence of antibiotic resistance and pathogenicity potential in 40 E. faecalis isolated from 10 Italian raw milk cheeses over a 13-year period (1997-2009). Among the 14 tested antibiotics, resistance to tetracycline, rifampicin, chloramphenicol, and erythromycin was observed, whereas vancomycin-resistant enterococci were not found. A high incidence (90% of strains) of the tet(M) gene emerged, whereas tet(K), tet(S), tet(L), int, and ermB genes were occasionally amplified (12.5%, 10%, 7.5%, 2.5% and 30%, respectively). No strain was positive for vancomycin-resistant determinants. Among the seven virulence determinants considered, the asa1, gelE, esp, and efaA genes were harbored. No other gene encoding for either different virulence factors (cylA, hyl, and ace) or amino acid decarboxylase activity (hdc, tdc, and odc) was detected. Consequently, E. faecalis isolated from raw milk cheeses does not represent a substantial reservoir of antimicrobial resistance and virulence factors if compared with clinical strains. However, this species occasionally harbors detrimental traits; thus, the possibility that it could be a route for transmission of pathogenic genes through dairy products should never be disregarded.

Comparative genomic analysis of Enterococcus faecalis: insights into their environmental adaptations

BACKGROUND

Enterococcus faecalis is widely studied as a common gut commensal and a nosocomial pathogen. In fact, Enterococcus faecalis is ubiquitous in nature, and it has been isolated from various niches, including the gastrointestinal tract, faeces, blood, urine, water, and fermented foods (such as dairy products). In order to elucidate the role of habitat in shaping the genome of Enterococcus faecalis, we performed a comparative genomic analysis of 78 strains of various origins.

RESULTS

Although no correlation was found between the strain isolation habitat and the phylogeny of Enterococcus faecalis from our whole genome-based phylogenetic analysis, our results revealed some environment-associated features in the analysed Enterococcus faecalis genomes. Significant differences were found in the genome size and the number of predicted open reading frames (ORFs) between strains originated from different environments. In general, strains from water sources had the smallest genome size and the least number of predicted ORFs. We also identified 293 environment-specific genes, some of which might link to the adaptive strategies for survival in particular environments. In addition, the number of antibiotic resistance genes was significantly different between strains isolated from dairy products, water, and blood. Strains isolated from blood had the largest number of antibiotic resistance genes.

CONCLUSION

These findings improve our understanding of the role of habitat in shaping the genomes of Enterococcus faecalis.

Investigation of antimicrobial activity and entA and entB genes in Enterococcus faecium and Enterococcus faecalis strains isolated from naturally fermented Turkish white cheeses

In this research, the antagonistic effects of Enterococcus faecalis and E. faecium bacteria isolated from naturally fermented Turkish white cheeses, produced without starter culture, against Listeria monocytogenes, L. innocua, L. ivanovii, Staphylococcus aureus, and E. faecalis were evaluated. The presence of entA and entB genes was also detected in the isolates, which had antimicrobial activity. Total 71 strains of E. faecalis and 7 strains of E. faecium were tested; 20 of E. faecalis and none of E. faecium strains showed antimicrobial activity against the tested bacteria using agar spot method. Among E. faecalis strains, which had antimicrobial activity, three strains contained both entA and entB genes, two strains carried only entA gene, and five strains had only entB gene. These cheese-sourced enterococcal strains or their enterocins should be considered to be used for food preservation especially in the dairy industry.

Lactic acid microbiota identification in water, raw milk, endogenous starter culture, and fresh Minas artisanal cheese from the Campo das Vertentes region of Brazil during the dry and rainy seasons

Minas artisanal cheese, produced in the Campo das Vertentes region of Brazil, is made from raw milk and endogenous starter cultures. Although this cheese is of great historical and socioeconomic importance, little information is available about its microbiological and physical-chemical qualities, or about its beneficial microbiota. This work was aimed at evaluating the qualities of the cheese and the components used for its production, comparing samples collected during the dry and rainy seasons. We also conducted molecular identification and isolated 50 samples of lactic acid bacteria from cheese (n=21), water (n=3), raw milk (n=9), and endogenous starter culture (n=17). The microbiological quality of the cheese, water, raw milk, and endogenous starter culture was lower during the rainy period, given the higher counts of coagulase-positive Staphylococcus and total and thermotolerant coliforms. Enterococcus faecalis was the lactic acid bacteria isolated most frequently (42.86%) in cheese samples, followed by Lactococcus lactis (28.57%) and Lactobacillus plantarum (14.29%). Lactobacillus brevis (5.88%), Enterococcus pseudoavium (5.88%), Enterococcus durans (5.88%), and Aerococcus viridans (5.88%) were isolated from endogenous starter cultures and are described for the first time in the literature. The lactic acid bacteria identified in the analyzed cheeses may inhibit undesirable microbiota and contribute to the safety and flavor of the cheese, but this needs to be evaluated in future research.