Technological and safety properties display biodiversity among enterococci isolated from two Egyptian cheeses, "Ras" and "Domiati"

Current Trends of Enterococci in Dairy Products: A Comprehensive Review of Their Multiple Roles

As a genus that has evolved for resistance against adverse environmental factors and that readily exchanges genetic elements, enterococci are well adapted to the cheese environment and may reach high numbers in artisanal cheeses. Their metabolites impact cheese flavor, texture, and rheological properties, thus contributing to the development of its typical sensorial properties. Due to their antimicrobial activity, enterococci modulate the cheese microbiota, stimulate autolysis of other lactic acid bacteria (LAB), control pathogens and deterioration microorganisms, and may offer beneficial effects to the health of their hosts. They could in principle be employed as adjunct/protective/probiotic cultures; however, due to their propensity to acquire genetic determinants of virulence and antibiotic resistance, together with the opportunistic character of some of its members, this genus does not possess Qualified Presumption of Safety (QPS) status. It is, however, noteworthy that some putative virulence factors described in foodborne enterococci may simply reflect adaptation to the food environment and to the human host as commensal. Further research is needed to help distinguish friend from foe among enterococci, eventually enabling exploitation of the beneficial aspects of specific cheese-associated strains. This review aims at discussing both beneficial and deleterious roles played by enterococci in artisanal cheeses, while highlighting the need for further research on such a remarkably hardy genus.

Assessment of virulence factors, antibiotic resistance and amino-decarboxylase activity in Enterococcus faecium MXVK29 isolated from Mexican chorizo

Enterococcus faecium MXVK29 has the ability to produce an antimicrobial compound that belongs to Class IIa of the Klaenhammer classification, and could be used as part of a biopreservation technology through direct inoculation of the strain as a starter or protective culture. However, Enterococcus is considered as an opportunistic pathogen, hence, the purpose of this work was to study the food safety determinants of E. faecium MXVK29. The strain was sensitive to all of the antibiotics tested (penicillin, tetracycline, vancomycin, erythromycin, chloramphenicol, gentamicin, neomycin, kanamycin and netilmicin) and did not demonstrate histamine, cadaverine or putrescine formation. Furthermore, tyrosine-decarboxylase activity was detected by qualitative assays and PCR. Among the virulence factors analysed for the strain, only the genes encoding the sexual pheromone cCF10 precursor lipoprotein (ccf) and cell-wall adhesion (efaA_fm ) were amplified. The presence of these genes has low impact on pathogenesis, as there are no other genes encoding for virulence factors, such as aggregation proteins. Therefore, Enterococcus faecium could be employed as part of a bioconservation method, because it does not produce risk factors for consumer's health; in addition, it could be used as part of the hurdle technology in foods.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of molecular techniques has allowed, in recent years, to detect pathogenicity genes present in the genome of starter cultures used in food processing and preservation. The presence of these genes is undesirable, because horizontal transfer may occur with the natural biota of consumers. For this reason, it is important to analyse the presence of pathogenicity genes in such cultures. In this work, virulence factors and antibiotic resistance of Enterococcus faecium strain MXVK29, producing an antimicrobial compound with high antilisterial activity, were analysed. The results indicate that the strain is safe to be used in food processing as starter culture.

Antibiotic susceptibility and heterogeneity in technological traits of lactobacilli isolated from Algerian goat's milk

The objective of this study was to identify and study the heterogeneity of technological traits of lactobacilli from goat's milk of Algeria and to evaluate in vitro their safety aspect. Using API50 CHL system and 16S rDNA sequencing, 51 % of strains were assigned as Lactobacillus plantarum, 34 % as L. pentosus, 7 % as L. rhamnosus and 8 % as L. fermentum. A large variability was noted for the acidifying capacity in skim milk after 6, 12 and 24 h of incubation. All strains expressed aminopeptidase activity against alanine-ρ-NA and leucine-ρ-NA at different levels. All strains were resistant to vancomycin and most of strains showed more susceptibility to β-lactam antibiotic. High susceptibility toward the inhibitors of protein synthesis was also observed. Minimum inhibitory concentrations data obtained revealed that isolates were susceptible to penicillin and chloramphenicol, and resistant to gentamicin and vancomycin. Minimum inhibitory concentrations distribution of other antibiotics showed variability. The analysis of graphical representation of principal component analysis of technological properties of L. plantarum and L. pentosus strains showed diversity among the isolates. Finally, eight L. plantarum (LAM1, LAM3, LAM21, LAM25, LAM35, LF15, LAM34, and LAM35), four L. pentosus (LAM38, LAM39, LF9 and LF16) and two L. rhamnosus (LF3 and LF10) strains, could be good candidates as adjunct culture in dairy product in Algeria.