Antimicrobial characterization and safety aspects of the bacteriocinogenic Enterococcus hirae F420 isolated from Moroccan raw goat milk

Isolation and characterization of bioprotective lactic acid bacteria from Moroccan fish and seafood

The microbiota of aquatic animals is heavily influenced by their environment, offering a potential source for biotechnologically relevant microorganisms. In this investigation, bacterial strains from fish and fish products were investigated to determine their antimicrobial effects against fish and food pathogens. Twelve strains, including five Lactococcus, two Enterococcus hirae, two Enterococcus mundtii, and three Latilactobacillus sakei were selected as producing bacteriocin-like substances with antimicrobial properties that were active against a broad spectrum of bacteria, such as Listeria monocytogenes, Staphylococcus aureus, and Pseudomonas aeruginosa. Selected strains were identified via 16S rRNA sequencing. Most strains exhibited sensitivity to eight types of antibiotics (erythromycin, tetracycline, chloramphenicol, vancomycin, fosfomycin, gentamicin, ampicillin, and netilmicin), lacked hemolysin and gelatinase virulence factors, and did not produce histamine. These findings suggest that marine fish may be a promising source of lactic acid bacteria strains with antimicrobial potential for use as biopreservatives in the food industry.

Anti-adherence Activity of Monomicrobial and Polymicrobial Food-Derived Enterococcus spp. Biofilms Against Pathogenic Bacteria

Enterococcus species are commensal organisms of the gastrointestinal tract and can also be isolated from traditional food products. They are used as probiotics in animals and less often in humans. This study aimed to investigate the antibacterial and anti-adhesive activities of twelve food-origin Enterococcus spp. biofilms on stainless steel AISI 316 L against foodborne pathogens, including Listeria monocytogenes CECT4032, Pseudomonas aeruginosa ATCC27853, and Escherichia coli ATCC25922. The antimicrobial and co-aggregation abilities of Enterococcus spp. were evaluated using spots-agar test and spectrophotometry aggregation assay, respectively. The anti-adhesive activity of selected strains on pathogenic bacteria was tested using serial dilution technique. Enterococci strains in planktonic mode showed strong inhibition activity against different pathogens tested with a significant difference in co-aggregation capacity. Moreover, L. monocytogenes and E. coli presented a low auto-aggregation rate compared to P. aeruginosa, which showed an amount of 11.25%. Scanning electron microscopy (SEM) revealed that biofilm biomass of Enterococcus spp. increased after 10 days. The thick layer of enterococci biofilms on AISI 316 L caused a low adhesion of L. monocytogenes, resulting in a reduction of approximately 2.8 log CFU/cm² for some selected strains. Additionally, Enterococcus monocultures' biofilms were more efficient than polymicrobial cultures (a cocktail of enterococci strains) in controlling pathogen adhesion. These results indicate that monocultures of Enterococcus spp. biofilms could be used to prevent the adhesion of pathogenic bacteria on AISI 316 L.

In Vitro Probiotic Characterization and Safety Assessment of Lactic Acid Bacteria Isolated from Raw Milk of Japanese-Saanen Goat (Capra hircus)

Two novel probiotic strains of lactic acid bacteria were successfully isolated from the raw milk of dairy Japanese-Saanen goats. Selection criteria for positive candidates were grown on de Man-Rogosa-Sharpe or M17 selective medium at 30, 35, or 42 °C anaerobically, and characterized based on Gram reaction, catalase test, and tolerance to low pH and bile salts. Among the 101 isolated positive candidates, two strains, YM2-1 and YM2-3, were selected and identified as Lacticaseibacillus rhamnosus using 16S rDNA sequence similarity. Culture supernatants of the two strains exhibited antipathogenic activity against Salmonella enterica subsp. enterica serovar. Typhimurium, Shigella sonnei, methicillin-resistant Staphylococcus aureus, methicillin-sensitive Staphylococcus aureus, Listeria monocytogenes, and Escherichia coli O157. The antipathogenic activities were retained to some extent after neutralization, indicating the presence of antipathogenic substances other than organic acids in the culture supernatants. The two strains were sensitive with coincidental minimum inhibition concentrations (indicated in the parentheses hereafter) to ampicillin (0.25 μg/mL), chloramphenicol (4 μg/mL), gentamycin (4 μg/mL), kanamycin (64 μg/mL), streptomycin (16 μg/mL), and tetracycline (4 μg/mL). Furthermore, the two strains were resistant to clindamycin (16 μg/mL) and erythromycin (4 μg/mL). In addition, both YM2-1 and YM2-3 strains showed less unfavorable activities, including bile acid bioconversion, carcinogenic-related enzymes, mucin degradation, plasminogen activation, and hemolysis, than the detection limits of in vitro evaluation methods used in this study. In summary, L. rhamnosus YM2-1 and YM2-3 are highly safe and promising probiotic strains applicable in the dairy industry, and were first isolated from the raw milk of Japanese-Saanen goats.

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.

Physiological and molecular insights of bacteriocin production by Enterococcus hirae ST57ACC from Brazilian artisanal cheese

The bacteriocinogenic Enterococcus hirae ST57ACC recently isolated from a Brazilian artisanal cheese was subjected here to additional analyses in order to evaluate its bacteriocin production and the potential influence of ABC transporter system in its expression. Besides these physiological and molecular aspects, the bacteriocin was evaluated for its cytotoxicity against HT-29. Differences in the inoculum size had no impact on the growth of E. hirae ST57ACC; however, the bacteriocin was only produced after 9 h of growth when the strain was inoculated at 5% or 10% (v/v), with similar levels of bacteriocin production obtained by both conventional growth and batch fermentation. Furthermore, potential expression of ABC transporters corresponding to the bacteriocin transport and sugar metabolism was identified. In terms of adverse effects, when a semi-purified fraction of the bacteriocin and the cell-free supernatant were tested against HT-29, total cell viability was similar to observed on untreated cells, indicating the absence of cytotoxic effect. Based on the obtained results, E. hirae ST57ACC can produce its bacteriocin at industrial level by using bioreactors, its bacteriocin expression is potentially influenced by the ABC transporter system, and no cytotoxic effects were observed on HT-29 cells, indicating its potential use as a bio-preservative.

Screening of the Enterocin-Encoding Genes and Their Genetic Determinism in the Bacteriocinogenic Enterococcus faecium GHB21

Enterococci are well-known for their ability to produce a variety of antimicrobial peptides called enterocins. Most of these enterocins withstand extreme conditions and are very effective against a broad spectrum of undesirable bacteria including some Gram-negative bacteria. The same enterococci strain can produce multiple enterocins simultaneously. The genetic determinants of these bacteriocins can either be located on plasmids or on bacterial chromosome. Digestion of Enterococcus faecium GHB21 plasmids with various restriction endonucleases suggests the presence of two plasmids named pGHB-21.1 and pGHB-21.2 whose respective sizes are ~ 10.0 kb and ~ 3.3 kb. The screening of enterocin-encoding genes among E. faecium GHB21 genome by PCR followed by amplicon sequencing indicated the presence of three different enterocin structural genes similar to entA, entB, and entP genes previously detected in other E. faecium strains. These enterocin genes were, subsequently, localized on the bacterial chromosome based on PCR-targeted screening using total DNA and plasmids of E. faecium GHB21 as separate templates.

Occurrence, molecular and antimicrobial resistance of Enterococcus spp. isolated from raw cow's milk trade by street trading in Meknes city, Morocco

Background

Enterococcus spp. belongs to a group of pathogens which are responsible for serious infections. This study aims at highlighting the raw milk microbiological contamination and at providing data for prevalence and antimicrobial resistance of Enterococcus spp. isolated from raw cow's milk marketed (without any pasteurization) by street traders.

Methods

During the period of May 2015 through April 2016, 150 cow's raw milk samples were collected from street traders in Meknes city. They were examined for the identification of Enterococcus spp. using biochemical tests and 16S rRNA gene sequencing. The antimicrobial susceptibility of the isolates was determined.

Results

The results showed that 11.3% (17/150) of samples were positive for the presence of Enterococcus spp., of which 64.7% were identified as Enterococcus faecalis, 17.6% as Enterococcus faecium, 11.8% as Enterococcus durans and 5.9% as Enterococcus hirae. The antimicrobial susceptibility showed that all Enterococcus spp. were resistant to ampicillin. The species E. faecalis, E. faecium, E. durans and E. hirae were resistant to streptomycin, with percentages of 52.9% (9/17), 11.8% (2/17), 11.8% (2/17), and 5.9% (1/17) respectively. All isolated strains of E. faecalis and E. faecium were resistant to tetracycline. The multiple antibiotic resistance index was elevated in the majority of Enterococcus spp., reaching values higher than 0.5, indicating a risk for public health.

Conclusion

This study shows that the raw milk consumed by the population is contaminated with strains of Enterococcus resistant to antibiotics used in breeding for prophylactic purposes. This requires raising the awareness of those involved in the production and marketing of milk, so as to take measures to apply good hygienic practices and rationalize the use of zootechnical antibiotics.