Enterococcus crotali sp. nov., isolated from faecal material of a timber rattlesnake

Enterococci as a One Health indicator of antimicrobial resistance

The rapid increase of antimicrobial-resistant bacteria in humans and livestock is concerning. Antimicrobials are essential for the treatment of disease in modern day medicine, and their misuse in humans and food animals has contributed to an increase in the prevalence of antimicrobial-resistant bacteria. Globally, antimicrobial resistance is recognized as a One Health problem affecting humans, animals, and environment. Enterococcal species are Gram-positive bacteria that are widely distributed in nature. Their occurrence, prevalence, and persistence across the One Health continuum make them an ideal candidate to study antimicrobial resistance from a One Health perspective. The objective of this review was to summarize the role of enterococci as an indicator of antimicrobial resistance across One Health sectors. We also briefly address the prevalence of enterococci in human, animal, and environmental settings. In addition, a 16S RNA gene-based phylogenetic tree was constructed to visualize the evolutionary relationship among enterococcal species and whether they segregate based on host environment. We also review the genomic basis of antimicrobial resistance in enterococcal species across the One Health continuum.

The mechanism of Enterococcus faecium on the virulence of Listeria monocytogenes during the storage of fermented sausages by whole genome analysis

This study investigated the safety characteristics and potential probiotic properties of Enterococcus faecium by using whole genome analysis, and then explored the effect of this strain on the virulence of Listeria monocytogenes in vitro and during the storage of fermented sausages. Results showed that E. faecium B1 presented enterocin A, B, and P, enterolysin A, and UviB, and the exotoxin related genes and exoenzyme related genes were not detected in the genome of E. faecium B1. However, the adherence genes including acm and scm were present in this strain, which also positively correlated with characteristics related to probiotic potential. In addition, E. faecium could adapt to the condition of fermented sausages, and decrease the survival of L. monocytogenes in vitro and in vivo. The expression of the virulence genes (prfA, hly, inlA, and inlB) and sigB-related genes (prli42, rsbT, rsbU, rsbV, rsbW, and sigB) were all inhibited by E. faecium B1 to different extents during the storage of fermented sausages at 4 °C. Moreover, compared with the E. faecium B1 group, the expression level of entA, entB, and entP genes of E. faecium B1 in the co-culture of fermented sausages was increased during the storage, which may be the inhibition mechanism of E. faecium B1 on L. monocytogenes. These results demonstrated that E. faecium B1 could potentially be used as bio-protection to control L. monocytogenes in meat products.

Bacteriocin production and technological properties of Enterococcus mundtii and Enterococcus faecium strains isolated from sheep and goat colostrum

Enterococci are lactic acid bacteria (LAB) that play a role in the aroma formation, maturation, and sensory development of fermented foods such as meat and dairy products. They also contribute to the improvement of the extended shelf life of fermented foods by producing bacteriocin. The aim of this study was to isolate bacteriocin-producing LAB from sheep and goat colostrum, to characterize the bacteriocin-producing strains, and determine the technological properties of the strains. A total of 13 bacteriocin-producing LAB was isolated and identified as 11 Enterococcus mundtii and two Enterococcus faecium. The strains were found to be genetically different from each other by phylogenetic analysis of 16S rRNA gene sequences and random amplified polymorphic-DNA (RAPD-PCR). It has been determined that bacteriocins show activity in a wide pH range and are resistant to heat, lose their activity with proteolytic enzymes and α-amylase, but are resistant to detergents. While the presence of the munKS gene was detected in all of the strains, it was determined that E. faecium HC121.4, HC161.1, E. mundtii HC147.1, HC166.5, and HC166.8 strains contained multiple enterocin genes. Trisin-SDS-PAGE analysis revealed two active protein bands of approximately 5.1 and 5.5 kDa in E. faecium HC121.4 and one active protein band with a weight of approximately 4.96 kDa in other strains. E. mundtii strains and E. faecium HC161.1 were identified as mundticin KS producers, and E. faecium HC121.4 was defined as an enterocin A and B producer. Except for E. mundtii HC166.8, acid production of strains was found to be slow at 6 h and moderate at 24 h. None of them showed extracellular proteolytic and lipolytic activities. It was found that the strains had esterase, esterase lipase, leucine arylamidase, acid phosphatase, and naphthol-AS-Bl-phosphohydrolase activities, while protease activities were low and peptidase activities were high. In conclusion, bacteriocin producer 13 Enterococcus strains isolated from sheep and goat colostrum were found to have the potential to be included in starter culture combinations.

Vagococcus zengguangii sp. nov., isolated from yak faeces

Two unknown Gram-stain-positive, catalase- and oxidasenegative, non-motile, and coccus-shaped bacteria, designated MN-17^T and MN-09, were isolated from yaks faeces (Bos grunniens) in the Qinghai-Tibet Plateau of China. 16S rRNA gene sequence-based comparative analyses revealed that the two strains were grouped within the genus Vagococcus, displaying the highest similarity with Vagococcus xieshaowenii CGMCC 1.16436^T (98.6%) and Vagococcus elongatus CCUG 51432^T (96.4%). Both strains grew optimally at 37°C and pH 7.0 in the presence of 0.5% (w/v) NaCl. The complete genome of MN-17^T comprises 2,085 putative genes with a total of 2,190,262 bp and an average G + C content of 36.7 mol%. The major fatty acids were C_16:0 (31.2%), C_14:0 (28.5%), and C_18:1ω9c (13.0%); the predominant respiratory quinone was MK-7 (68.8%); the peptidoglycan type was A4α(L-Lys-D-Asp); and the major polar lipid was diphosphatidylglycerol. Together, these supported the affiliation of strain MN-17^T to the genus Vagococcus. In silico DNA-DNA hybridization and the average nucleotide identity values between MN-17^T and all recognized species in the genus were 21.6-26.1% and 70.7-83.0%, respectively. MN-17^T produced acid from D-cellobiose, D-fructose, glycerol, D-glucose, N-acetyl-glucosamine, gentiobiose, D-mannose, D-maltose, D-ribose, D-saccharose, salicin, D-trehalose, and D-xylose. These results distinguished MN-17^T and MN-09 from closely related species in Vagococcus. Thus, we propose that strains MN-17^T and MN-09 represent a novel species in the genus Vagococcus, with the name Vagococcus zengguangii sp. The type strain is MN-17^T (= CGMCC 1.16726^T = GDMCC 1.1589^T = JCM 33478^T).

Safety, beneficial and technological properties of enterococci for use in functional food applications - a review

Enterococci are ubiquitous lactic acid bacteria (LAB) that predominantly reside in the gastrointestinal tract of humans and animals but are also widespread in food and the environment due to their robust nature. Enterococci have the paradoxical position of providing several benefits of technological interest in food fermentations but are also considered as opportunistic pathogens capable of causing infection in immunocompromised patients. Several species of the genus have been correlated with disease development in humans such as bacteremia, urinary tract infections, and endocarditis. The pathogenesis of enterococci has been attributed to the increasing incidence of antibiotic resistance and the possession of virulence determinants. On the contrary, enterococci have led to improvements in the aroma, texture, and flavor of fermented dairy products, while their beneficial use as probiotic and protective cultures has also been documented. Furthermore, they have emerged as important candidates for the generation of bioactive peptides, particularly from milk, which provide new opportunities for the development of functional foods and nutraceuticals for human nutrition and health. The detection of pathogenic traits among some species is compromising their use in food applications and subsequently, the genus neither has Generally Regarded as Safe (GRAS) status nor has it been included in the Qualified Presumption of Safety (QPS) list. Nevertheless, the use of certain enterococcal strains in food has been permitted on the basis of a case-by-case assessment. Promisingly, enterococcal virulence factors appear strain specific and food isolates harbor fewer determinants than clinical isolates, while they also remain largely susceptible to clinically relevant antibiotics and thus, have a lower potential for pathogenicity. Ideally, strains considered for use in foods should not possess any virulence determinants and should be susceptible to clinically relevant antibiotics. Implementation of an appropriate risk/benefit analysis, establishment of a strain's innocuity, and consideration for relevant guidelines, legislation, and regulatory aspects surrounding functional food development, may help industry, health-staff and consumers accept enterococci, like other LAB, as important candidates for useful and beneficial applications in food biotechnology.

Vagococcus bubulae sp. nov., isolated from ground beef, and Vagococcus vulneris sp. nov., isolated from a human foot wound

Two unusual catalase-negative, Gram-stain-positive, Vagococcus-like isolates that were referred to the CDC Streptococcus Laboratory for identification are described. Strain SS1994^T was isolated from ground beef and strain SS1995^T was isolated from a human foot wound. Comparative 16S rRNA gene sequence analysis of isolates SS1994^T and SS1995^T against Vagococcus type strain sequences supported their inclusion in the genus Vagococcus. Strain SS1994^T showed high sequence similarity (>97.0 %) to the two most recently proposed species, Vagococcus martis (99.2 %) and Vagococcus teuberi (99.0 %) followed by Vagococcus penaei (98.8 %), strain SS1995^T (98.6 %), Vagococcus carniphilus (98.0 %), Vagococcus acidifermentans (98.0 %) and Vagococcus fluvialis (97.9 %). The 16S rRNA gene sequence of strain SS1995^T was most similar to V. penaei (99.1 %), followed by SS1994^T (98.6 %), V. martis (98.4 %), V. teuberi (98.1 %), V. acidifermentans (97.8 %), and both V. carniphilus and V. fluvialis (97.5 %). A polyphasic taxonomic study using conventional biochemical and the rapid ID 32 STREP system, MALDI-TOF MS, cell fatty acid analysis, pairwise sequence comparisons of the 16S rRNA, rpoA, rpoB, pheS and groL genes, and comparative core and whole genome sequence analyses revealed that strains SS1994^T and SS1995^T were two novel Vagococcus species. The novel taxonomic status of the two isolates was confirmed with core genome phylogeny, average nucleotide identity <84 % and in silico DNA-DNA hybridization <28 % to any other Vagococcus species. The names Vagococcusbubulae SS1994^T=(CCUG 70831^T=LMG 30164^T) and Vagococcusvulneris SS1995^T=(CCUG 70832^T=LMG 30165^T) are proposed.

Enterococcus wangshanyuanii sp. nov., isolated from faeces of yaks (Bos grunniens)

The taxonomic position of four phenotypically closely related strains isolated from faecal samples of yaks (Bos grunniens) collected from the Qinghai-Tibetan plateau, China, was determined by a polyphasic approach. The strains were non-spore-forming, non-motile Gram-stain-positive, ovoid cocci, occurring predominantly in pairs and short chains or in irregular clusters. The 16S rRNA gene of strain MN05^T was related phylogenetically to those of Enterococcushaemoperoxidus, Enterococcusrotai, Enterococcusquebecensis, Enterococcusplantarum, Enterococcuscrotali, Enterococcusmoraviensis, Enterococcussilesiacus, Enterococcuscaccae, Enterococcustermitis, Enterococcusureasiticus and Enterococcusureilyticus, all belonging to the Enterococcusfaecalis species group. The sequence similarities of three selected genes of MN05^T to those of the type strains of phylogenetically related species were measured, with values within the range of 99.2-99.5 % (16S rRNA gene), 90.0-97.3 % (rpoA) and 80.0-85.3 % (pheS), respectively. The genome of MN05^T (3 842 361 bp) contained 4299 genes with a DNA G+C content of 37.5 mol%. A whole-genome phylogenetic tree based on 808 core genes confirmed that MN05^T belongs to a distinct lineage, well separated from all recognized species of the Enterococcusfaecalis species group. DNA-DNA hybridization in silico showed that MN05^T displayed less than 70 % DNA-DNA relatedness with the other 13 species of the Enterococcusfaecalis species group. Moreover, their phenotypic features distinguished the four strains from the other species of the Enterococcusfaecalis species group. Based upon these data obtained from the polyphasic characterization performed in the present study, a novel species of the genus Enterococcus, Enterococcus wangshanyuanii sp. nov., is proposed, with the type strain MN05^T (=DSM 104047^T=CGMCC 1.15942^T).