Reevaluation of the taxonomic status of recently described species of Enterococcus: evidence that E. thailandicus is a senior subjective synonym of "E. sanguinicola" and confirmation of E. caccae as a species distinct from E. silesiacus

Non-faecium non-faecalis enterococci: a review of clinical manifestations, virulence factors, and antimicrobial resistance

SUMMARYEnterococci are a diverse group of Gram-positive bacteria that are typically found as commensals in humans, animals, and the environment. Occasionally, they may cause clinically relevant diseases such as endocarditis, septicemia, urinary tract infections, and wound infections. The majority of clinical infections in humans are caused by two species: Enterococcus faecium and Enterococcus faecalis. However, there is an increasing number of clinical infections caused by non-faecium non-faecalis (NFF) enterococci. Although NFF enterococcal species are often overlooked, studies have shown that they may harbor antimicrobial resistance (AMR) genes and virulence factors that are found in E. faecium and E. faecalis. In this review, we present an overview of the NFF enterococci with a particular focus on human clinical manifestations, epidemiology, virulence genes, and AMR genes.

Effect of Intragenomic Sequence Heterogeneity among Multiple 16S rRNA Genes on Species Identification of Elizabethkingia

Accurate identification of Elizabethkingia species mostly requires the use of molecular techniques, and 16S rRNA gene sequencing is generally considered the method of choice. In this study, we evaluated the effect of intraspecific diversity among the multiple copies of the 16S rRNA gene on the accuracy of species identification in the genus Elizabethkingia. Sequences of 16S rRNA genes obtained from the 32 complete whole-genome sequences of Elizabethkingia deposited in GenBank and from 218 clinical isolates collected from 5 hospitals in Taiwan were analyzed. Four or five copies of 16S rRNA were identified in the Elizabethkingia species with complete genome sequences. The dissimilarity among the copies of the16S rRNA gene was <1% in all Elizabethkingia strains. E. meningoseptica demonstrated a significantly higher rate of nucleotide variations in the 16S rRNA than did E. anophelis (P = 0.011). Nucleotide alterations occurred more frequently in regions V2 and V6 than in other hypervariable regions (P < 0.001). E. meningoseptica, E. anophelis, and E. argenteiflava strains were clustered distinctly in the phylogenetic tree inferred from 16S rRNA genes, and the intragenomic variation of gene sequences had no profound effect on the classification of taxa. However, E. miricola, E. bruuniana, E. ursingii, and E. occulta were grouped closely in the phylogenetic analysis, and the variation among the multiple copies of the 16S rRNA in one E. ursingii strain affected species classification. Other marker genes may be required to supplement the species classification of closely related taxa in the genus Elizabethkingia. IMPORTANCE Incorrect identification of bacterial species would influence the epidemiology and clinical analysis of patients infected with Elizabethkingia. The results of the present study suggest that 16S rRNA gene sequencing should not be considered the gold standard for the accurate identification of Elizabethkingia species.

Electricity production and key exoelectrogens in a mixed-culture psychrophilic microbial fuel cell at 4 °C

The electricity production via psychrophilic microbial fuel cell (PMFC) for wastewater treatment in cold regions offers an alternative to avoid the unwanted methane dissolution of traditional anaerobic fermentation. But, it is seldom reported by mixed-culture, especially closed to 0 °C. Thus, a two-chamber mixed-culture PMFC at 4 °C was successfully operated in this study using acetate as an electron donor. The main results demonstrated a good performance of PMFC, including the maximum voltage of 513 mV at 1000 Ω, coulombic efficiency of 53%, and power density of 689 mW/m². The cyclic voltammetry curves of enriched biofilm showed a direct electron transfer pathway. These good performances of mixed-culture PMFC were due to the high psychrophilic activity of enriched biofilm, including exoelectrogens genera of Geobacter (6.1%), Enterococcus (17.5%), and Clostridium_sensu_stricto_12 (3.8%). Consequently, a mixed-culture PMFC provides a reasonable strategy to enrich exoelectrogens with high activity. For low-temperature regions, the mixed-culture PMFC involved biotechnologies shall benefit energy generation and valuable chemical production in the future. KEY POINTS: • PMFC showed a maximum voltage of around 513 mV under a resistance of 1000 Ω. • The coulombic efficiency was 53% and the max power density was 689 mW/m². • Geobacter, Enterococcus, and Clostridium_sensu_stricto_12 were key exoelectrogens.

Identification and safety assessment of Enterococcus thailandicus TC1 isolated from healthy pigs

Enterococci have the dual characteristics of being opportunistic pathogens and promising probiotics. The isolation from patients of CDC PNS-E2, a newly described Enterococcus species Enterococcus sanguinicola, may pose potential hazards. Enterococcus thailandicus from fermented sausage is a senior subjective synonym of E. sanguinicola. In this study, Enterococcus thailandicus TC1 was first isolated in healthy pigs in Tongcheng, China and identified by phenotypic analysis and 16S rRNA-based techniques. To evaluate the strain safety, an approach including virulence factors, antibiotic resistance, and animal experiments was adopted. The results show that cylA, gelE, esp, agg, ace, efaAfm, efaAfs, ptsD genes were undetected, and that the strain was sensitive or poorly resistant to some clinically relevant antibiotics. However, the isolated strain demonstrated β-hemolytic activity in rabbit blood agar plates. Analysis of animal experiments revealed that the isolated strain had no adverse effect on translocation and the internal organ indices, though significant differences in histology (villi height, crypts height) of ileum were observed. The data acquired suggest that E. thailandicus TC1 may be associated with a potential health risk.

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.

Revisiting the taxonomy of the genus Elizabethkingia using whole-genome sequencing, optical mapping, and MALDI-TOF, along with proposal of three novel Elizabethkingia species: Elizabethkingia bruuniana sp. nov., Elizabethkingia ursingii sp. nov., and Elizabethkingia occulta sp. nov

The genus Elizabethkingia is genetically heterogeneous, and the phenotypic similarities between recognized species pose challenges in correct identification of clinically derived isolates. In addition to the type species Elizabethkingia meningoseptica, and more recently proposed Elizabethkingia miricola, Elizabethkingia anophelis and Elizabethkingia endophytica, four genomospecies have long been recognized. By comparing historic DNA-DNA hybridization results with whole genome sequences, optical maps, and MALDI-TOF mass spectra on a large and diverse set of strains, we propose a comprehensive taxonomic revision of this genus. Genomospecies 1 and 2 contain the type strains E. anophelis and E. miricola, respectively. Genomospecies 3 and 4 are herein proposed as novel species named as Elizabethkingia bruuniana sp. nov. (type strain, G0146^T = DSM 2975^T = CCUG 69503^T = CIP 111191^T) and Elizabethkingia ursingii sp. nov. (type strain, G4122^T = DSM 2974^T = CCUG 69496^T = CIP 111192^T), respectively. Finally, the new species Elizabethkingia occulta sp. nov. (type strain G4070^T = DSM 2976^T = CCUG 69505^T = CIP 111193^T), is proposed.

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

A facultatively anaerobic, Gram-stain-positive bacterium, designated ETRF1T, was found in faecal material of a timber rattlesnake (Crotalus horridus). Based on a comparative 16S rRNA gene sequence analysis, the isolate was assigned to the genus Enterococcus. The 16S rRNA gene sequence of strain ETRF1T showed >97 % similarity to that of the type strains of Enterococcus rotai, E. caccae, E. silesiacus, E haemoperoxidus, E. ureasiticus, E. moraviensis, E. plantarum, E. quebecensis, E. ureilyticus, E. termitis, E. rivorum and E. faecalis. The organism could be distinguished from these 12 phylogenetically related enterococci using conventional biochemical testing, the Rapid ID32 Strep system, comparative pheS and rpoA gene sequence analysis, and comparative whole genome sequence analysis. The estimated in silico DNA-DNA hybridization values were <70 %, and average nucleotide identity values were <96 %, when compared to these 12 species, further validating that ETRF1T represents a unique species within the genus Enterococcus. On the basis of these analyses, strain ETRF1T (=CCUG 65857T=LMG 28312T) is proposed as the type strain of a novel species, Enterococcus crotali sp. nov.

Modified 16S-23S rRNA intergenic region restriction endonuclease analysis for species identification of Enterococcus strains isolated from pigs, compared with identification using classical methods and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Fast and reliable identification of bacteria to at least the species level is currently the basis for correct diagnosis and appropriate treatment of infections. This is particularly important in the case of bacteria of the genus Enterococcus, whose resistance profile is often correlated with their species (e.g. resistance to vancomycin). In this study, we evaluated restriction endonuclease analysis of the 16S-23S rRNA gene intergenic transcribed spacer (ITS) region for species identification of Enterococcus. The utility of the method was compared with that of phenotypic methods [biochemical profile evaluation and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS)]. Identification was based on 21 Enterococcus reference strains, of the species E. faecalis, E. faecium, E. hirae, E. durans, E. casseliflavus, E. gallinarum, E. avium, E. cecorum and E. columbae, and 47 Enterococcus field strains isolated from pigs. Restriction endonuclease analysis of the ITS-PCR product using HinfI, RsaI and MboI, in the order specified, enabled species differentiation of the Enterococcus reference and field strains, and in the case of the latter, the results of species identification were identical (47/47) to those obtained by MALDI-TOF MS. Moreover, as a result of digestion with MboI, a unique restriction profile was also obtained for the strains (3/3) identified by MALDI-TOF MS as E. thailandicus. In our opinion, restriction endonuclease analysis of the 16S-23S rRNA gene ITS region of Enterococcus may be a simple and relatively fast (less than 4 h) alternative method for identifying the species occurring most frequently in humans and animals.

Enterococci in the environment

Enterococci are common, commensal members of gut communities in mammals and birds, yet they are also opportunistic pathogens that cause millions of human and animal infections annually. Because they are shed in human and animal feces, are readily culturable, and predict human health risks from exposure to polluted recreational waters, they are used as surrogates for waterborne pathogens and as fecal indicator bacteria (FIB) in research and in water quality testing throughout the world. Evidence from several decades of research demonstrates, however, that enterococci may be present in high densities in the absence of obvious fecal sources and that environmental reservoirs of these FIB are important sources and sinks, with the potential to impact water quality. This review focuses on the distribution and microbial ecology of enterococci in environmental (secondary) habitats, including the effect of environmental stressors; an outline of their known and apparent sources, sinks, and fluxes; and an overview of the use of enterococci as FIB. Finally, the significance of emerging methodologies, such as microbial source tracking (MST) and empirical predictive models, as tools in water quality monitoring is addressed. The mounting evidence for widespread extraenteric sources and reservoirs of enterococci demonstrates the versatility of the genus Enterococcus and argues for the necessity of a better understanding of their ecology in natural environments, as well as their roles as opportunistic pathogens and indicators of human pathogens.

Transferable multiresistance plasmids carrying cfr in Enterococcus spp. from swine and farm environment

Seventy-seven porcine Enterococcus isolates with florfenicol MICs of ≥16 μg of were/ml screened for the presence of the multiresistance gene cfr, its location on plasmids, and its genetic environment. Three isolates-Enterococcus thailandicus 3-38 (from a porcine rectal swab collected at a pig farm), Enterococcus thailandicus W3, and Enterococcus faecalis W9-2 (the latter two from sewage at a different farm), carried the cfr gene. The SmaI pulsed-field gel electrophoresis patterns of the three isolates differed distinctly. In addition, E. faecalis W9-2 was assigned to a new multilocus sequence type ST469. Mating experiments and Southern blot analysis indicated that cfr is located on conjugative plasmids pW3 (∼75 kb) from E. thailandicus W3, p3-38 (∼72 kb) from E. thailandicus 3-38, and pW9-2 (∼55 kb) from E. faecalis W9-2; these plasmids differed in their sizes, additional resistance genes, and the analysis of the segments encompassing the cfr gene. Sequence analysis revealed that all plasmids harbored a 4,447-bp central region, in which cfr was bracketed by two copies of the novel insertion sequence ISEnfa4 located in the same orientation. The sequences flanking the central regions of these plasmids, including the partial tra gene regions and a ω-ε-ζ toxin-antitoxin module, exhibited >95% nucleotide sequence identity to the conjugative plasmid pAMβ1 from E. faecalis. Conjugative plasmids carrying cfr appear to play an important role in the dissemination and maintenance of the multiresistance gene cfr among enterococcal isolates and possibly other species of Gram-positive bacteria.