Molecular Characteristics of Enterococcus faecalis and Enterococcus faecium from Bulk Tank Milk in Korea

Assessment of the Safety and Probiotic Properties of Enterococcus faecium B13 Isolated from Fermented Chili

Enterococcus faecium B13, selected from fermentation chili, has been proven to promote animal growth by previous studies, but it belongs to opportunistic pathogens, so a comprehensive evaluation of its probiotic properties and safety is necessary. In this study, the probiotic properties and safety of B13 were evaluated at the genetic and phenotype levels in vitro and then confirmed in vivo. The genome of B13 contains one chromosome and two plasmids. The average nucleotide identity indicated that B13 was most closely related to the fermentation-plant-derived strain. The strain does not carry the major virulence genes of the clinical E. faecium strains but contains aac(6')-Ii, ant (6)-Ia, msrC genes. The strain had a higher tolerance to acid at pH 3.0, 4.0, and 0.3% bile salt and a 32.83% free radical DPPH clearance rate. It can adhere to Caco-2 cells and reduce the adhesion of E. coli to Caco-2 cells. The safety assessment revealed that the strain showed no hemolysis and did not exhibit gelatinase, ornithine decarboxylase, lysine decarboxylase, or tryptophanase activity. It was sensitive to twelve antibiotics but was resistant to erythromycin, rifampicin, tetracycline, doxycycline, and minocycline. Experiments in vivo have shown that B13 can be located in the ileum and colon and has no adverse effects on experiment animals. After 28 days of feeding, B13 did not remarkable change the α-diversity of the gut flora or increase the virulence genes. Our study demonstrated that E. faecium B13 may be used as a probiotic candidate.

Biofilm formation by heat-resistant dairy bacteria: multispecies biofilm model under static and dynamic conditions

In the food industry, especially dairy, biofilms can be formed by heat-resistant spoilage and pathogenic bacteria from the farm. Such biofilms may persist throughout the processing chain and contaminate milk and dairy products continuously, increasing equipment cleaning, maintenance costs, and product recalls. Most biofilms are multispecies, yet most studies focus on single-species models. A multispecies model of dairy biofilm was developed under static and dynamic conditions using heat-resistant Bacillus licheniformis, Pseudomonas aeruginosa, Clostridium tyrobutyricum, Enterococcus faecalis, Streptococcus thermophilus, and Rothia kristinae isolated from dairies. C. tyrobutiricum and R. kristinae were weak producers of biofilm, whereas the other four were moderate to strong producers. Based on cross-streaking on agar, P. aeruginosa was found to inhibit B. licheniformis and E. faecalis. In multispecies biofilm formed on stainless steel in a CDC reactor fed microfiltered milk, the strong biofilm producers were dominant while the weak producers were barely detectable. All biofilm matrices were dispersed easily by proteinase K treatment but were less sensitive to DNase or carbohydrases. Further studies are needed to deepen our understanding of multispecies biofilms and interactions within to develop improved preventive strategies to control the proliferation of spoilage and pathogenic bacteria in dairies and other food processing environments. IMPORTANCE A model of multispecies biofilm was created to study biofilm formation by heat-resistant bacteria in the dairy industry. The biofilm formation potential was evaluated under static conditions. A continuous flow version was then developed to study multispecies biofilm formed on stainless steel in microfiltered milk under dynamic conditions encountered in dairy processing equipment. The study of biofilm composition and bacterial interactions therein will lead to more effective means of suppressing bacterial growth on food processing equipment and contamination of products with spoilage and pathogenic bacteria, which represent considerable economic loss.

Low prevalence of antimicrobial resistant organisms (methicillin resistant Staphylococcus aureus, extended beta-lactamase producing Enterobacteriaceae, and vancomycin resistant enterococci) in bulk tank milk in New South Wales, Australia

OBJECTIVE

Estimate the presence of methicillin resistant Staphylococcus aureus (MRSA), extended beta-lactamase (ESBL) producing Enterobacteriaceae, and vancomycin resistant enterococci (VRE) in bulk tank milk in dairy herds in New South Wales (NSW), Australia.

METHODS

Bulk tank milk samples (n = 80) were collected from dairy farms (n = 40, i.e. 2 per farm) in NSW during 2021. Bacteria were cultured using selective chromogenic indicator media with isolate identity confirmed using biochemical testing, Gram stain, and MALDI-TOF mass spectroscopy. Antimicrobial resistance (AMR) was confirmed using antibiotic disk diffusion.

RESULTS

No samples tested positive to the targeted AMR organisms.

CONCLUSION

The prevalence of MRSA, ESBL-producing Enterobacteriaceae, and VRE is low in NSW dairy herds.

The Emergence of Antimicrobial Resistance and Virulence Characteristics in Enterococcus Species Isolated from Bovine Milk

Enterococcus spp., including E. faecalis and E. faecium, pose risks to dairy farms as opportunistic pathogens. The study evaluates antimicrobial resistance (AMR) and virulence characteristics of Enterococcus spp. isolated from bovine milk. Bile esculin agar was used to assess 1471 milk samples, followed by colony identification, gram staining, catalase tests, and 45 °C incubation. PCR analysis targeted E. faecalis and E. faecium in characteristic Enterococcus spp. colonies, with MALDI-TOF used for negative samples. Multiple tests, including disk diffusion, chromogenic VRE agar for vancomycin resistance, Vancomycin Etest® for MIC determination, and PCR for virulence factors (cylA, esp, efaA, ace, asa1, gelE, and hyl genes), were performed. Out of 100 identified strains, E. durans (30.66%), E. faecium (26.28%), and E. faecalis (18.25%) were predominant. AMR in Enterococcus spp. varied, with the highest rates against rifampicin (27%), tetracycline (20%), and erythromycin (18%). Linezolid (5%), vancomycin, ciprofloxacin, and teicoplanin (3% each) had lower prevalence. E. faecium and E. faecalis showed high AMR to rifampicin, erythromycin, and tetracycline. Thirty-two strains (18.98%) grew on VRE Chromoselect agar, while 4 (2 E. faecalis and 2 E. faecium) showed vancomycin resistance by MIC values. E. faecalis carried gelE (45.5%) and asa1 (36%), and E. gallinarum had 9.1% with the asa1 gene. Detecting resistant Enterococcus in bovine milk supports control strategies for enterococci on dairy farms, highlighting AMR concerns in the food chain.

Genetic characterization of MDR genomic elements carrying two aac(6')-aph(2″) genes in feline-derived clinical Enterococcus faecalis isolate

Multidrug-resistant Enterococcus faecalis (E. faecalis) often cause intestinal infections in cats. The aim of this study was to investigate a multidrug-resistant E. faecalis isolate for plasmidic and chromosomal antimicrobial resistance and their genetic environment. E. faecalis strain ESC1 was obtained from the feces of a cat. Antimicrobial susceptibility testing was carried out using the broth microdilution method. Conjugation experiments were performed using Escherichia coli and Staphylococcus aureus as receptors. Complete sequences of chromosomal DNA and plasmids were generated by whole genome sequencing (WGS) and bioinformatics analysis for the presence of drug resistance genes and mobile elements. Multidrug-resistant E. faecalis ESC1 contained a chromosome and three plasmids. The amino acid at position 80 of the parC gene on the chromosome was mutated from serine to isoleucine, and hence the amino acid mutation at this site led to the resistance of ESC1 strain to fluoroquinolones. Eleven antibiotic resistance genes were located on two plasmids. We identified a novel composite transposon carrying two aminoglycoside resistance genes aac(6')-aph(2″). This study reported the coexistence of a novel 5.4 kb composite transposon and a resistance plasmid with multiple homologous recombination in an isolate of E. faecalis ESC1. This data provides a basis for understanding the genomic signature and antimicrobial resistance mechanisms of this pathogen.

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.

Sensitive and Selective Detection of Enterococcus faecalis Using a New Turn-on Fluorogenic β-glucosidase Substrate Combined with a Modified Selective Broth

A new, simple-to-synthesize and sensitive turn-on fluorogenic substrate (CFMU-Glu) for β-glucosidase activity was developed. This probe was based on a 7-hydroxycoumarin derivative (CFMU) that could emit green fluorescence and had the low pK_a value of 5.61 ± 0.01. CFMU-Glu could be used for sensitive monitoring of the almond βGLU and Enterococcus faecalis (E. faecalis) at the optimal pHs of 6.50 and 7.00, respectively. Moreover, a new sensitive and selective fluorogenic broth (PBF-B) for E. faecalis, utilizing CFMU-Glu and polymyxin B, was also developed. Polymyxin B was discovered to can significantly improve the detection selectivity and signal intensity. The proposed 4-four method using PBF-B and a microcentrifuge tube could provide fluorogenic detection limits of 5.01 × 10⁴ and 1.0 × 10⁵  CFU mL^-1 by fluorescence microplate reader and naked eye, respectively; it could also provide a turn-on chromogenic detection limit of 1.0 × 10⁶  CFU mL^-1 by naked eye. The proposed method could detect 8 CFU mL^-1 of E. faecalis in drinking water, Liangcha (herbal tea) and milk samples within 10 h, without pre-enrichment.

Antimicrobial Resistance, Virulence Profiles, and Public Health Significance of Enterococcus faecalis Isolated from Clinical Mastitis of Cattle in Bangladesh

This study was designed to identify Enterococcus faecalis from clinical mastitis of cattle and determine their antimicrobial resistance and virulence determinants to evaluate their potential public health significance. A total of 105 composite milk samples (80 from cattle with clinical mastitis and 25 from apparently healthy cattle) were analyzed. E. faecalis were isolated by culturing on enterococcal selective media and identified by PCR and sequencing. Antimicrobial resistance phenotype was elucidated by the disc diffusion method, and MIC was determined by broth microdilution method according to CLSI guidelines. Detection of antimicrobial resistance and virulence genes was done by PCR. E. faecalis were isolated from 11.25% (9/80) of the clinical mastitis and 4% (1/25) of the apparently healthy cattle milk samples. The disc diffusion test revealed 40% isolates as resistant to tetracycline and azithromycin, respectively. Among them, 20% (2/10) of isolates showed resistance to both tetracycline and azithromycin. Tetracycline-resistant isolates showed MIC ranging from ≥64 to >128 μg/ml and carried tetracycline-resistant genes tetK, tetL, and tetM in 25%, 25%, and 50% of the resistant isolates, respectively. On the other hand, all the isolates were sensitive to amoxicillin, ampicillin, bacitracin, chloramphenicol, gentamicin, penicillin, and vancomycin. In addition, the isolates carried at least one of the nine virulence genes screened with pil having the highest frequency, followed by fsrB, fsrC, ace, sprE, gelE, and agg genes. Positive correlations were evident between ace, fsrC, gelE, and sprE genes that are associated with the attachment and biofilm formation in E. faecalis. E. faecalis isolated in this study carried antibiotic resistance and virulence determinants which explain their competence to be potential human pathogens.

Clinical isolates of E. faecalis and E. faecium harboring virulence genes show the concomitant presence of CRISPR loci and antibiotic resistance determinants

In this study, we evaluated the antimicrobial susceptibility, the presence of gene-encoding virulence factors and CRISPR systems, as well as the ability to produce lytic enzymes among clinical E. faecalis and E. faecium isolates (n = 44). All enterococci isolates showed phenotypes of multidrug resistance. E. faecalis and E. faecium isolates exhibited high-level aminoglycoside resistance phenotype, several of them harboring the aac(6')Ie-aph(2″)Ia and aph(3')-IIIa genes. The gene vanA was the most frequent among vancomycin-resistant E. faecium. High prevalence of the virulence genes esp and efaA were observed; hyl gene was more associated with E. faecium, while ace and efaA genes were more frequently detected in E. faecalis. Caseinase activity was frequently detected among the isolates. Gelatinase and DNAse activities predominated among E. faecalis, while hemolytic capability was frequent among E. faecium isolates. Twenty-nine isolates showed at least one CRISPR system investigated. Several enterococci isolates harbored the aac(6')-Ie-aph(2″)-Ia or aph(3')-IIIa genes and a CRISPR loci. CRISPR loci were positively correlated to efaA and gelE genes, and gelatinase and DNAse activities, while CRISPR loci absence was related to hyl gene presence. These results show that clinical isolates of E. faecalis and E. faecium harboring virulence genes show the concomitant presence of CRISPR loci and antibiotic resistance determinants.

Genetic Diversity, Antimicrobial Resistance, and Virulence Factors of Enterococcus Faecalis Isolates Obtained from Stool Samples of Hospitalized Patients

Background: Enterococcus faecalis rapidly develops resistance to different antibiotics, thereby resulting in serious nosocomial infections associated with high mortality rates and different problems in the healthcare systems. Objectives: This study aimed to analyze the genetic diversity, antimicrobial resistance, and virulence factors of E. faecalis isolates obtained from the stool samples of patients in a hospital in the center of Iran. Methods: In this cross-sectional descriptive-analytical study, 108 stool samples were collected from September 2019 to February 2020 from 108 patients hospitalized in a hospital in the center of Iran. Enterococcus faecalis isolates were detected using the ddlE gene detection technique, and antimicrobial resistance testing was performed using the disc agar diffusion method. Moreover, polymerase chain reaction (PCR) was used to detect antimicrobial resistance genes and virulence factors. Genetic diversity was also analyzed by enterobacterial repetitive intergenic consensus using PCR (ERIC-PCR). The BioNumerics software was used to construct a dendrogram. Results: Of 108 isolates, 50 samples were E. faecalis (46.2%). The prevalence of multidrug resistance among E. faecalis isolates was 62%, and most isolates were resistant to antibiotics tetracycline (70%), erythromycin (68%), and rifampin (60%). Among the E. faecalis isolates, the most prevalent antimicrobial resistance genes were ermB (96%), aph (2′′) Ia (66%), aac(6′)-Ie (40%), and ermC (30%), and the most prevalent virulence genes were gelE (78%), asa1 (74%), and esp (74%). The genetic diversity analysis showed 25 ERIC types in two major clusters (ie, clusters H and J) and eight minor clusters (ie, clusters A-G and I). There was no significant difference between clusters H and J in terms of antimicrobial resistance and resistance genes (P > 0.05). In contrast, the prevalence of the asa1 gene was significantly higher in cluster J than in cluster H (P < 0.05). Conclusions: This study showed the high prevalence of multidrug resistance, and high heterogeneity among the E. faecalis isolates obtained from the stool samples of hospitalized patients.

Prevalence and Virulence Characteristics of Enterococcus faecalis and Enterococcus faecium in Bovine Mastitis Milk Compared to Bovine Normal Raw Milk in South Korea

Enterococcus spp. are pathogens that cause environmental mastitis and are difficult to eliminate owing to their resistance to antibiotics. To compare the virulence characteristics of isolates from bovine mastitis milk (BMM) and bovine normal raw milk (NRM), we isolated Enterococcus spp. from 39 dairy farms in South Korea from 2015−2020. A total of 122 Enterococcus spp. were identified, with Enterococcus faecalis (73.8%) accounting for the majority, followed by Enterococcus faecium (26.2%). E. faecalis isolated from BMM harbored gelE, asa1, esp, and cylA genes with a prevalence of 85.7, 71.4, 54.3, and 30.0%, respectively. These genes were significantly more abundant in BMM than in NRM, except for asa1 (p < 0.0001). Interestingly, strong biofilm and gelatinase formation was predominately observed for BMM isolates and this was significantly correlated to the presence of esp and gelE genes (p < 0.05). BMM isolates demonstrated higher resistance to tetracycline (59.3%), followed by chloramphenicol (21.0%), rifampicin (18.5%), doxycycline (4.9%), ciprofloxacin (1.2%), and nitrofurantoin (1.2%), than those from NRM. E. faecalis harboring esp, gelE, and cylA may be causative agents for bovine mastitis and act as a reservoir for the transmission of virulence factors to humans.

Single Molecule Real-Time Sequencing and Traditional Cultivation Techniques Reveal Complex Community Structures and Regional Variations of Psychrotrophic Bacteria in Raw Milk

In this study, we investigated the species composition and diversity of psychrotrophic bacteria in raw milk from Heilongjiang, Inner Mongolia, Gansu, Henan, Anhui, Jiangsu, Chongqing, and Hunan provinces in China using traditional cultivation and PacBio Single Molecule Real-Time sequencing methods. The isolated psychrotrophic bacteria were highly diverse, which composed of 21 genera and 59 species. Pseudomonas accounted for 58.9% of the total genera while Stenotrophomonas and Enterococcus were also highly represented (above 5.0%). In particular, P. azotoformans occurred at a level of 16.9% and P. paralactis, P. lactis, E. faecalis, and P. marginalis were present in relatively high proportions (above 4.0%). Regional differences were found significantly among the test regions except samples from Heilongjiang and Inner Mongolia were similar. Additionally, differences were observed between days in Henan, Anhui, and Jiangsu samples. Therefore, control strategies must be implemented on regional and season basis.

Antimicrobial resistance, virulence genes and biofilm formation in Enterococcus species isolated from milk of sheep and goat with subclinical mastitis

This study is designed to discuss the antimicrobial resistance, virulence determinants and biofilm formation capacity of Enterococcus spp. isolated from milk of sheep and goat with subclinical mastitis in Qena, Egypt. The obtained isolates were identified by the VITEK2 system and 16S rDNA sequencing as E. faecalis, E. faecium, E. casseliflavus and E. hirae. Overall, E. faecalis and E. faecium were the dominant species recovered from mastitic milk samples. The antimicrobial susceptibility test evidenced multidrug resistance of the isolates against the following antimicrobials: oxacillin (89.2.%), followed by vancomycin (75.7%) and linezolid (70.3%). Also, most of these isolates (73%) could form biofilms. For example, 18.9% of Enterococcus strains formed strong biofilm, whereas 32.4% of isolates formed moderate biofilm and 21.6% of isolates formed weak biofilm. The most prevalent resistance genes found in our isolates were blaZ (54%), vanA (40%), ermB (51.4%), tetM (13.5%) and optrA (10.8%). Moreover, asa1 (37.8%), cylA (42.3%), gelE (78.4%), esp (32.4%), EF3314(48.6%) and ace (75.5%) were the most common virulence genes. A significant correlation was found between biofilm formation, multidrug resistance and virulence genes of the isolates. This study highlights several aspects of virulence and harmfulness of Enterococcus strains isolated from subclinical mastitic milk, which necessitates continuous inspection and monitoring of dairy animals.

Comparative Analysis of Chloramphenicol-Resistant Enterococcus faecalis Isolated from Dairy Companies in Korea

Although chloramphenicol is currently banned from use in livestock, other phenicols, such as florfenicol and thiamphenicol, have been used for the treatment of bacterial infections in domestic cattle in Korea. This study compares the characteristics of chloramphenicol-resistant Enterococcus faecalis isolated from the bulk tank milk of four major dairy companies in Korea. Although the distribution of multidrug resistance patterns showed no significant differences between the four companies, 85 chloramphenicol-resistant Enterococcus faecalis isolates showed a significantly high number of resistances against five or six antimicrobial classes (37.6%, respectively) (p < 0.05). When analyzing the distribution of phenicol resistance genes, 31 (36.5%) isolates only carried the catA gene, and two (6.3%) isolates from company A only carried the cfr gene. No isolates carried the catB or fexA genes. Regarding the distribution of other resistance genes, both the tetL and tetM (45.9%), ermB (82.4%), and both aac(6″)-Ie-aph(2″)-la and ant(6′)-Ia genes (30.6%) showed a high prevalence, and the optrA and poxtA genes were observed separately, each in only two (2.4%) isolates. Our results confirm that the dissemination of chloramphenicol-resistant Enterococcus faecalis and some antimicrobial resistance genes show significant differences between dairy companies. Therefore, our results support that each dairy company should undertake effective surveillance programs to better understand and minimize the emergence of resistance on a multidisciplinary level.

Characteristics of High-Level Aminoglycoside-Resistant Enterococcus faecalis Isolated from Bulk Tank Milk in Korea

Enterococci, which are considered environmental mastitis-causing pathogens, have easily acquired aminoglycoside-resistant genes that encode various aminoglycoside-modifying enzymes (AME). Therefore, this study was conducted to compare the distribution of high-level aminoglycoside-resistant (HLAR) and multidrug-resistant (MDR) Enterococcus faecalis (E. faecalis) bacteria isolated from bulk tank milk in four dairy companies in Korea. Moreover, it analyzed the characteristics of their antimicrobial resistance genes and virulence factors. Among the 301 E. faecalis bacteria studied, 185 (61.5%) showed HLAR with no significant differences among the dairy companies. Furthermore, 129 (69.7%) of the 185 HLAR E. faecalis showed MDR without significant differences among companies. In contrast, HLAR E. faecalis from companies A, B, and C were significantly higher in resistance to the four classes than those in company D, which had the highest MDR ability against the three antimicrobial classes (p < 0.05). In addition, in the distribution of AME genes, 72 (38.9%) and 36 (19.5%) of the isolates carried both aac(6')Ie-aph(2″)-la and ant(6)-Ia genes, and the ant (6)-Ia gene alone, respectively, with significant differences among the companies (p < 0.05). In the distribution of virulence genes, the ace (99.5%), efa A (98.9%), and cad 1 (98.4%) genes were significantly prevalent (p < 0.05). Thus, our results support that an advanced management program by companies is required to minimize the dissemination of antimicrobial resistance and virulence factors.