ANTIBIOTIC RESISTANCE OF ENTEROCOCCAL ISOLATES IN RAW MILK

Analysis of Antibiotic-Resistant and Virulence Genes of Enterococcus Detected in Calf Colostrum-One Health Perspective

Enterococci are considered among the most prevalent global multidrug-resistant microorganisms globally. Their dissemination is a global concern, particularly by food-producing animals for both animals and humans. The aim of this study was to identify the species and investigate the antibiotic resistance and virulence profile of Enterococcus in bovine colostrum. Out of 88 presumptive Enterococcus isolates, species identification and susceptibility to 14 antimicrobials were tested using the disk diffusion method. An analysis of the antibiotic resistance and virulence genes was performed on the most prevalent species, using specific PCR assays. Enterococcus faecalis (54.5%), E. faecium (14.8%) and E. gallinarum (6.8%) were the identified species. To the best of our knowledge, this is the first report of E. gallinarum in bovine colostrum. The majority of the isolates showed resistance to quinupristin-dalfopristin (95.9%), erythromycin (80.7%), tetracycline (80.7%) and streptomycin (58%). Ninety-two percent of isolates were classified as multidrug-resistant. The most frequently detected resistance genes were tet(K) (61.1%), tet(M) (75.9%), tet(L) (90.7%), erm(B) (55.6%) and ant(6)-Ia (46.3%). The most prevalent virulence factors were cpd, esp, agg and cylL_L. Enterococcus faecium showed a higher probability of carrying the erm(C), tet(M), ace and gel(E) genes (p < 0.05). These results demonstrated that colostrum can constitute an important reservoir and vehicle for the dissemination of antibiotic resistance and virulence genes to the three niches included in a One Health perspective (humans, animals and the environment), highlighting the importance of hygiene sanitary measures to mitigate colostrum microbial contamination.

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.

Prevalence, seasonality, and growth of enterococci in raw and pasteurized milk in Victoria, Australia

This study investigated the prevalence, seasonality, and species variety of enterococci present in raw milk factory silos and pasteurized milk in 3 dairying regions in Victoria, Australia, over a 1-yr period. Additionally, the growth ability of thermoduric enterococci isolated in this study (Enterococcus faecalis, E. faecium, E. hirae, and E. durans) was determined in milk at temperatures likely to occur during storage, transport, and distribution, and before domestic consumption (4 and 7°C). Enterococci were detected in 96% of 211 raw milk samples, with an average count of 2.48 log10 cfu/mL. Counts were significantly lower in winter than summer (average 1.84 log10 cfu/mL) and were different between factories but not regions. Enterococcus faecalis was the most prevalent species isolated from raw milk in every factory, comprising between 61.5 and 83.5% of enterococcal species across each season. Enterococci were detected in lower numbers in pasteurized milk than in raw milk and were below the limit of detection on spread plates (<10 cfu/mL) after factory pasteurization. Residual viable cells were only detected following enrichment using 100-mL samples of milk, with 20.8% of the samples testing positive; this equated to a decrease in the average raw milk enterococci count of >4 log10 cfu/mL following pasteurization. Although E. faecalis predominated in raw milk and E. durans was found in only 2.9% of raw milk samples, E. durans was the most prevalent species detected in pasteurized milk. The detection of enterococci in the pasteurized milk did not correlate with higher enterococci counts in the raw milk. This suggested that the main enterococci populations in raw milk were heat-sensitive and that thermoduric enterococci survived pasteurization in a small numbers of instances. All of the thermoduric enterococci that were assessed for growth at likely refrigeration temperatures were able to grow at both 4 and 7°C in sterile milk, with generation times of 35 to 41h and 16 to 22h, respectively. Thermoduric enterococci were detected in pasteurized milk stored at 4°C for 2 wk (typically 1 to 9 cells/100mL, up to 2.82 log10 cfu/mL), demonstrating the potential of enterococci to survive pasteurization and contribute to milk spoilage at refrigeration temperatures. This is particularly relevant for milk that is aseptically packaged to exclude gram-negative psychrotrophic bacteria and kept above the recommended storage temperature of ≤5°C.

Presence of enterococci in cow milk and their antibiotic resistance

Enterococci represent an important part of contaminate microflora in raw milk and dairy products. They constitute significant part of nosocomial pathogens with a remarkable capacity of expressing resistance to several antimicrobial  agents. We aimed to assess occurrence and antibiotic resistance of enterococci in the raw milk samples and pasteurized milk samples. In this study total bacterial count, psychrotrophic count and count of enterococci were determine in raw milk cistern samples, storage tank milk samples and milk samples after pasteurization. A collection of 46 enterococcal isolates were identified and screened for their antibiotic resistance. Isolates of E. faecalis were dominant in raw milk samples (56.5 %). Sensitive to teicoplanine (30 mcg/disk) were 97.9 % of enterococcal isolates and 15.2 % isolates were resistant to vankomycin (30 mcg/disk).

Real time PCR for the rapid detection of vanA gene in surface waters and aquatic macrophyte by molecular beacon probe

Enterococci serve as an "indicator" of fecal contamination for recreational water quality. The vancomycin-resistant-enterococci (VRE) are emerging environmental contaminants in the surface waters. The aim ofthis study wasto develop a rapid and specific molecular beacon probe (MBP)-based real-time PCR assay for detection of vanA gene in surface waters and aquatic macrophyte. The limit of detection (LOD) of the MBP assay was 1 CFU/mL of VRE [r = 0.943; PCR efficiency = 99.7%] in 2-fold dilution format within 2.5 h and demonstrated high specificityfor environmental enterococci isolates exhibiting VanA phenotype (n=25). VRE were detected from downstream surface waters of the rivers impacted by point sources of pollution and recreational activities.The probe detected vanA gene in rootmat associated microbiota of E. crassipes (Mart) Solms. an aquatic nuisance weed, at eutrophic sites of the surface waters (ANOVA p < 0.001). In addition, the assay enabled detection of otherwise nondetectable vanA gene concentration in the upstream sites of two Indian rivers (Student's ttest p < 0.001). The MBP assay developed can be used for sensitive and rapid detection of VRE in surface waters and identification of nonpoint sources of pollution for implementation of preventive measures to protect human health.