Molecular analysis of artisanal Italian cheeses reveals Enterococcus italicus sp. nov

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.

Biofunctional attributes and storage study of milk fermented by Enterococcus italicus

Lactic acid bacteria are probiotics in the intestines and have been widely used as natural antioxidants in the food industry. In this study, Enterococcus italicus FM5 with strong antioxidant ability was isolated from fresh milk. The safety evaluation showed that E. italicus FM5 was sensitive to ampicillin, chloramphenicol, erythromycin, vancomycin, rifampicin, and tetracycline, and was not hemolytic. Meanwhile, the whole genome information and biofunctional attributes of this strain were determined and analyzed. Subsequently, E. italicus FM5 was co-cultured with traditional yogurt starters (Streptococcus thermophilus and Lactobacillus bulgaricus) to make fermented milk. The results showed that the addition of E. italicus FM5 could improve the oxygen free radical scavenging ability of the fermented milk, and the scavenging rates of DPPH, ABTS, OH-, and O2- radicals reaching up to 95.54 %, 88.35 %, 93.65 %, and 60.29 %, respectively. Furthermore, the addition of E. italicus FM5 reduced the curd time and improved the water holding capacity of the fermented milk. Besides, the growth of Lb. bulgaricus was significantly promoted when co-cultured with E. italicus FM5, thus the survival cells were increased compared with the traditional fermentation processes. Therefore, this study emphasized the potential to manufacture fermented milk by the co-cultivation of E. italicus with traditional yogurt starters.

The impact of environmental conditions and milk type on microbial communities of wooden vats and cheeses produced therein

Wooden vats are used in the production of some traditional cheeses as the biofilms on wooden vat surfaces are known to transfer large quantities of microbes to cheese. Variability in microbial communities on wooden vats could lead to inconsistent cheese production. In the present study, the influences of environmental conditions and milk type (raw or heat-treated) on the microbial composition of vat biofilms and cheeses made in the vats were studied using amplicon sequencing of bacterial 16S rRNA and fungal internal transcribed spacer genes. Results showed that the microbial composition of biofilms was influenced by environmental conditions but not the milk type used in cheese production. The microbial composition of cheeses can be further affected by bacterial contributions from milk and the selective forces of environmental conditions. Results of this study suggest that controlling environmental conditions could maintain a more consistent microbial composition of biofilms on wooden vats and resulting cheeses. The use of wooden vats coupled with heat-treated milk at one or more stages of cheese production might be a viable approach to produce cheese with high microbial diversities and reduce risks of undesirable microbes related to food safety and quality.

Molecular characterization of five novel plasmids from Enterococcus italicus SD1 isolated from fermented milk: An insight into understanding plasmid incompatibility

Enterococcal plasmids have attracted considerable interest because of their indispensable role in the pathogenesis and dissemination of multidrug-resistance. In this work, five novel plasmids pSRB2, pSRB3, pSRB4, pSRB5 and pSRB7 have been identified and characterised, coexisting in Eneterococcus italicus SD1 from fermented milk. The plasmids pSRB2, pSRB3 and pSRB5 were found to replicate via theta mode of replication while pSRB4 and pSRB7 were rolling-circle plasmids. Comparative analysis of SD1-plasmids dictated that the plasmids are mosaic with novel architecture. Plasmids pSRB2 and pSRB5 are comprised of a typical iteron-based class-A theta type origin of replication, whereas pSRB3 has a Class-D theta type replication origin like pAMβ1. The plasmids pSRB4 and pSRB7 shared similar ori as in pWV01. The SD1 class-A theta type plasmids shared significant homology between their replication proteins with differences in their DNA-binding domain and comprises of distinct iterons. The differences in their iterons and replication proteins restricts the "handcuff" formation for inhibition of plasmid replication, rendering to their compatibility to coexist. Similarly, for SD1 rolling circle plasmids the differences in the replication protein binding site in the origin and the replication protein supports their coexistence by inhibiting the crosstalk between the origins and replication proteins. The phylogenetic tree of their replication proteins revealed their distant kinship. The results indicate that the identified plasmids are unique to E. italicus SD1, providing further opportunities to study their utility in designing multiple gene expression systems for the simultaneous production of proteins in enterococci with the renewed concept of plasmid incompatibility.

Proposal of Enterococcus xinjiangensis Ren et al. 2020 as a later heterotypic synonym of Enterococcus lactis Morandi et al. 2012

Enterococcus lactis was published in the International Journal of Systematic and Evolutionary Microbiology in June 2012. Enterococcus xinjiangensis was published in Current Microbiology in 2016 and validated in November 2020. In the present study, the relationship between E. lactis and E. xinjiangensis was re-evaluated. In the 16S rRNA gene phylogeny, E. xinjiangensis was closely related to E. lactis and Enterococcus faecium. The type strains of E. xinjiangensis and E. lactis shared 99.8 % 16S rRNA gene sequence similarity, 98.5 % pheS sequence similarity, 99.9 % rpoA sequence similarity, 98.7 % average nucleotide identity (ANI) value and 88.9 % digital DNA-DNA hybridization (dDDH) value, indicating that they represent the same species. Meanwhile, although the type strains of E. xinjiangensis and E. faecium also shared 99.8 % 16S rRNA gene sequence similarity, 97.1 % pheS sequence similarity and 99.6 % rpoA sequence similarity, 94.7 % ANI and 59.1 % dDDH values indicated that they represent two different species. On the basis of the results present here, we propose Enterococcus xinjiangensis Ren et al. 2020 as a later heterotypic synonym of Enterococcus lactis Morandi et al. 2012.

Temporal dynamics of the fecal microbiota in veal calves in a 6-month field trial

BACKGROUND

Little is known about maturation of calves' gut microbiome in veal farms, in which animals are confined under intensive-farming conditions and the administration of collective antibiotic treatment in feed is common. We conducted a field study on 45 calves starting seven days after their arrival in three veal farms. We collected monthly fecal samples over six months and performed 16S rRNA gene sequencing and quantitative PCR of Escherichia coli to follow the dynamics of their microbiota, including that of their commensal E. coli populations. We used mixed-effect models to characterize the dynamics of α-diversity indices and numbers of E. coli, and searched for an effect of collective antibiotic treatments on the estimated parameters. On two farms, we also searched for associations between recommended daily doses of milk powder and bacterial abundance.

RESULTS

There was high heterogeneity between calves' microbiota upon their arrival at the farms, followed by an increase in similarity, starting at the first month. From the second month, 16 genera were detected at each sampling in all calves, representing 67.5% (± 9.9) of their microbiota. Shannon diversity index showed a two-phase increase, an inflection occurring at the end of the first month. Calves receiving antibiotics had a lower intercept estimate for Shannon index (- 0.17 CI95%[-0.27; - -0.06], p = 0.003) and a smaller number of E. coli/ gram of feces during the treatment and in the 15 days following it (- 0.37 log10 (E. coli/g) CI95%[- 0.66; - 0.08], p = 0.01) than unexposed calves. There were moderate to strong positive associations between the dose of milk powder and the relative abundances of the genera Megasphaera, Enterococcus, Dialister and Mitsuokella, and the number of E. coli (rs ≥ 0.40; Bonferroni corrected p < 0.05).

CONCLUSIONS

This observational study shows early convergence of the developing microbiota between veal calves and associations between the dose of milk powder and members of their microbiota. It suggests that administration of collective antibiotic treatment results in a reduction of microbial diversity and size of the E. coli population and highlights the need for additional work to fully understand the impact of antibiotic treatment in the veal industry.

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.

Antimicrobial Resistance in Enterococcus spp. of animal origin

Enterococci are natural inhabitants of the intestinal tract in humans and many animals, including food-producing and companion animals. They can easily contaminate the food and the environment, entering the food chain. Moreover, Enterococcus is an important opportunistic pathogen, especially the species E. faecalis and E. faecium, causing a wide variety of infections. This microorganism not only contains intrinsic resistance mechanisms to several antimicrobial agents, but also has the capacity to acquire new mechanisms of antimicrobial resistance. In this review we analyze the diversity of enterococcal species and their distribution in the intestinal tract of animals. Moreover, resistance mechanisms for different classes of antimicrobials of clinical relevance are reviewed, as well as the epidemiology of multidrug-resistant enterococci of animal origin, with special attention given to beta-lactams, glycopeptides, and linezolid. The emergence of new antimicrobial resistance genes in enterococci of animal origin, such as optrA and cfr, is highlighted. The molecular epidemiology and the population structure of E. faecalis and E. faecium isolates in farm and companion animals is presented. Moreover, the types of plasmids that carry the antimicrobial resistance genes in enterococci of animal origin are reviewed.

Approaches for enhancing in situ detection of enterocin genes in thermized milk, and selective isolation of enterocin-producing Enterococcus faecium from Baird-Parker agar

Enterococci are naturally selected for growth in thermized ewes'/goats' milk mixtures used for traditional cooked hard cheese processing in Greece. A culture-independent PCR-based approach was applied to detect the presence of enterocin-encoding genes in naturally culture-enriched thermized milk (TM). Portions of TM (63 °C, 30 s) collected from a commercial cheese plant before addition of starters were fermented at 37 °C for 48 h to facilitate growth of indigenous enterococci. The multiple enterocin-producing (m-Ent+) Enterococcus faecium KE82 and the nisin A-producing Lactococcus lactis subsp. cremoris M104 served as bacteriocin-positive inocula in separate TM treatments. The PCR results revealed a constant presence of the enterocin A, B and P genes in TM fermented naturally at 37 °C. Eleven out of 42 (26.2%) lactic isolates from the enriched TM cultures without inoculation were Ent+ E. faecium assigned to three biotypes. Biotype I (4 isolates) included single entA possessors, whereas biotype II (5 isolates) and biotype III (2 isolates) were m-Ent+ variants profiling entA-entB-entP and entA-entB genes, respectively. Biotype II displayed the strongest antilisterial activity in vitro. Surprisingly, 85.7% (6/7) of the m-Ent+ E. faecium were selectively isolated from Baird-Parker agar, reflecting their natural resistance to 0.01% tellurite contained in the egg yolk supplement. No cytolysin-positive E. faecalis or other Ent+ Enterococcus spp. were isolated. In conclusion, commercially thermized Greek milk is a natural pool or 'reservoir' of antagonistic Ent+ or m-Ent+ E. faecium strains that can be easily detected and recovered by applying this PCR-based approach to naturally fermented milks or cheese products.

The Peri-Implant and Periodontal Microbiota in Patients with and without Clinical Signs of Inflammation

Late implant failures, caused by the inflammation of surrounding tissues are a problem in implant dentistry. The path of bacterial transmission from teeth to implants is not completely understood. Therefore, the purpose of this study was to analyze intraindividual bacterial transmission characterizing subgingival microbiomes in teeth and implants, both in healthy subjects and in those with signs of periodontitis or peri-implantitis. Samples of peri-implant and dental sulcus fluid were collected. To identify the predominant microbiota, amplified fragments of bacterial 16S rRNA gene were separated by single strand conformation polymorphism analysis, sequenced and taxonomically classified. A total of 25 different predominant genera were found in the diseased group and 14 genera in the healthy group. Species richness did not differ significantly between implants, neighboring teeth and teeth with largest probing depth in the diseased group. Additionally, no differences between teeth and implants in the healthy group were detected. In contrast, microbial diversity varied between the different sampling points. Species richness is similar in healthy and diseased sites, but the composition of the bacterial community differed within the individual subjects. The underlying analyses strongly suggest that complete transmission from neighboring teeth to implants is unlikely.

Genomic comparative analysis of the environmental Enterococcus mundtii against enterococcal representative species

Background

Enterococcus mundtii is a yellow-pigmented microorganism rarely found in human infections. The draft genome sequence of E. mundtii was recently announced. Its genome encodes at least 2,589 genes and 57 RNAs, and 4 putative genomic islands have been detected. The objective of this study was to compare the genetic content of E. mundtii with respect to other enterococcal species and, more specifically, to identify genes coding for putative virulence traits present in enterococcal opportunistic pathogens.

Results

An in-depth mining of the annotated genome was performed in order to uncover the unique properties of this microorganism, which allowed us to detect a gene encoding the antimicrobial peptide mundticin among other relevant features. Moreover, in this study a comparative genomic analysis against commensal and pathogenic enterococcal species, for which genomic sequences have been released, was conducted for the first time. Furthermore, our study reveals significant similarities in gene content between this environmental isolate and the selected enterococci strains (sharing an “enterococcal gene core” of 805 CDS), which contributes to understand the persistence of this genus in different niches and also improves our knowledge about the genetics of this diverse group of microorganisms that includes environmental, commensal and opportunistic pathogens.

Conclusion

Although E. mundtii CRL1656 is phylogenetically closer to E. faecium, frequently responsible of nosocomial infections, this strain does not encode the most relevant relevant virulence factors found in the enterococcal clinical isolates and bioinformatic predictions indicate that it possesses the lowest number of putative pathogenic genes among the most representative enterococcal species. Accordingly, infection assays using the Galleria mellonella model confirmed its low virulence.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-489) contains supplementary material, which is available to authorized users.

Enterococcus olivae sp. nov., isolated from Spanish-style green-olive fermentations

Six strains of a hitherto unknown, Gram-stain-positive coccus were recovered from samples of Spanish-style green-olive fermentations. The 16S rRNA gene sequences from these isolates shared 98.7% and 98.5% of their nucleotide positions with those from Enterococcus saccharolyticus subsp. taiwanensis 812(T) and from E. saccharolyticus subsp. saccharolyticus ATCC 43076(T), respectively. The sequence of the rpoA gene in the isolates was 95% similar to that of E. saccharolyticus CECT 4309(T) ( = ATCC 43076(T)). The 16S rRNA and rpoA gene phylogenies revealed that the isolates grouped in a statistically well-supported cluster separate from E. saccharolyticus. Enzyme activity profiles as well as fermentation patterns differentiated the novel bacteria from other members of the Enterococcus genus. Finally, phenotypic, genotypic and phylogenetic data supported the identification of a novel species of the genus Enterococcus, for which the name Enterococcus olivae sp. nov. is proposed. The type strain is IGG16.11(T) ( = CECT 8063(T) = DSM 25431(T)).

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.

Genomic analysis reveals the biotechnological ability of Enterococcus italicus to produce glutathione

Through the analysis of the recently available genome shotgun sequence of Enterococcus italicus DSM 15952T type strain (Accession PRJNA61487, ID 61487), we found the presence of a gene encoding a bifunctional enzyme, termed γ-GCS-GS or GshF, involved in glutathione production and not influenced by feedback inhibition. The gshF gene exhibited high nucleotide and amino acid sequence similarity to other reported sequences from the Enterococcus genus and was constitutively expressed both in osmotic shock or in common cultural conditions. Several experimental studies concerning the culture medium, physiological stress, cell extract obtainment, and scaling-up showed that in selected conditions E. italicus was able to accumulate up to 250 μM of intracellular glutathione, which represented the main thiol group present into the cells. This is the first report regarding the production of glutathione by E. italicus, a species that could be used as a safe adjunct culture for glutathione-enriched dairy foods.

Taxonomic and molecular characterization of lactic acid bacteria and yeasts in nunu, a Ghanaian fermented milk product

Produced from raw unpasteurized milk, nunu is a spontaneously fermented yoghurt-like product made in Ghana and other parts of West Africa. Despite the importance of nunu in the diet of many Africans, there is currently only limited information available on the microorganisms associated with nunu processing. With the aim of obtaining a deeper understanding of the process and as a first step towards developing starter cultures with desired technological properties for nunu production, a microbiological characterization of nunu processing in three different towns in the Upper East region of Ghana, namely Bolgatanga, Paga and Navrongo, was carried out. Lactic acid bacteria (LAB) and yeasts associated with nunu processing were isolated and identified using a combination of pheno- and genotypic methods including morphological and carbohydrate fermentation tests, (GTG)5-based rep-PCR, multiplex PCR, and 16S and 26S rRNA gene sequencing. The LAB counts during nunu processing increased from 4.5 ± 0.4 log cfu/ml at 0 h to 8.7 ± 1.8 log cfu/ml at 24 h of fermentation while yeasts counts increased from 2.8 ± 1.2 log cfu/ml at 0 h to 5.8 ± 0.5 log cfu/ml by the end of fermentation. Lactobacillus fermentum was the dominant LAB throughout the fermentations with Lactobacillus plantarum and Leuconostoc mesenteroides playing prominent roles during the first 6-8 h of fermentation as well. Less frequently isolated LAB included Lactobacillus helveticus, Enterococcus faecium, Enterococcus italicus, Weissella confusa and a putatively novel Lactococcus spp. The yeasts involved were identified as Candida parapsilosis, Candida rugosa, Candida tropicalis, Galactomyces geotrichum, Pichia kudriavzevii and Saccharomyces cerevisiae with P. kudriavzevii and S. cerevisiae being the dominant yeast species.

Enterococcus lactis sp. nov., from Italian raw milk cheeses

Ten atypical Enterococcus strains were isolated from Italian raw milk cheeses. The 16S rRNA gene, phenylalanyl-tRNA synthase alpha subunit (pheS), RNA polymerase alpha subunit (rpoA) and the 16S–23S rRNA intergenic transcribed spacer (ITS) sequences, randomly amplified polymorphic DNA (RAPD) PCR and the phenotypic properties revealed that the isolates represent a novel enterococcal species. On the basis of 16S rRNA gene sequence analysis, the isolates were closely related to Enterococcus hirae ATCC 8043T, Enterococcus durans CECT 411T and Enterococcus faecium ATCC 19434T, with 98.8, 98.9 and 99.4 % sequence similarity, respectively. On the basis of sequence analysis of the housekeeping gene pheS, the reference strain, BT159T, occupied a position separate from E. faecium LMG 16198. The group of isolates could be easily differentiated from recognized species of the genus Enterococcus by 16S–23S rRNA ITS analysis, RAPD-PCR and phenotypic characteristics. The name Enterococcus lactis sp. nov. is proposed, with BT159T ( = DSM 23655T = LMG 25958T) as the type strain.

Genotypic intraspecies heterogeneity of Enterococcus italicus: data from dairy environments

The diversity of a collection of 19 Enterococcus italicus strains isolated from different dairy sources was explored using a molecular polyphasic approach, comprising random amplification of polymorphic DNA (RAPD-PCR), repetitive element PCR (REP-PCR), plasmid profiling and ribotyping. The data obtained showed a high-level of biodiversity, not always correlated to the niche of isolation. Particularly, REP-PCR with primer BOXA1R and plasmid profiling allowed the best discrimination at strain level. Exploiting the genome shotgun sequence of the type strain of the species, available in public database, genes related to insertion sequences present on enterococcal Pathogenic Islands (ISEf1, IS905), determinants related to virulence factors (codifying for hemolysin and cell wall surface proteins), exogenously DNA (conjugal transfer protein, replication plasmid protein, pheromone shutdown protein, phage integrase/recombinase) and penicillin binding proteins system were detected. The presence of most of these genes seemed a common genetic trait in the Enterococcus genus, sur gene (cell wall surface protein) was only detected in strains of E. italicus. To our knowledge, this is the first time that specific primers, with the expection of the species-specific probe targeted to 16S rRNA gene, have been designed for this species.

Enterococci as probiotics and their implications in food safety

Enterococci belong to the lactic acid bacteria (LAB) and they are of importance in foods due to their involvement in food spoilage and fermentations, as well as their utilisation as probiotics in humans and slaughter animals. However, they are also important nosocomial pathogens that cause bacteraemia, endocarditis and other infections. Some strains are resistant to many antibiotics and possess virulence factors such as adhesins, invasins, pili and haemolysin. The role of enterococci in disease has raised questions on their safety for use in foods or as probiotics. Studies on the incidence of virulence traits among enterococcal strains isolated from food showed that some can harbour virulence traits, but it is also thought that virulence is not the result of the presence of specific virulence determinants alone, but is rather a more intricate process. Specific genetic lineages of hospital-adapted strains have emerged, such as E. faecium clonal complex (CC) 17 and E. faecalis CC2, CC9, CC28 and CC40, which are high risk enterococcal clonal complexes. These are characterised by the presence of antibiotic resistance determinants and/or virulence factors, often located on pathogenicity islands or plasmids. Mobile genetic elements thus are considered to play a major role in the establishment of problematic lineages. Although enterococci occur in high numbers in certain types of fermented cheeses and sausages, they are not deliberately added as starter cultures. Some E. faecium and E. faecalis strains are used as probiotics and are ingested in high numbers, generally in the form of pharmaceutical preparations. Such probiotics are administered to treat diarrhoea, antibiotic-associated diarrhoea or irritable bowel syndrome, to lower cholesterol levels or to improve host immunity. In animals, enterococcal probiotics are mainly used to treat or prevent diarrhoea, for immune stimulation or to improve growth. From a food microbiological point of view, the safety of the bacteria used as probiotics must be assured, and data on the major strains in use so far indicate that they are safe. The advantage of use of probiotics in slaughter animals, from a food microbiological point of view, lies in the reduction of zoonotic pathogens in the gastrointestinal tract of animals which prevents the transmission of these pathogens via food. The use of enterococcal probiotics should, in view of the development of problematic lineages and the potential for gene transfer in the gastrointestinal tract of both humans and animals, be carefully monitored, and the advantages of using these and new strains should be considered in a well contemplated risk/benefit analysis.

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).

Designation of the provisional new enterococcus species CDC PNS-E2 as Enterococcus sanguinicola sp. nov., isolated from human blood, and identification of a strain previously named Enterococcus CDC PNS-E1 as Enterococcus italicus Fortina, Ricci, Mora, and Manachini 2004

We have previously characterized two new enterococcal species (provisionally designated CDC PNS-E1 and CDC PNS-E2) recovered from clinically significant specimens associated with invasive infections in humans. In the present report we provide additional data and propose formal denominations for isolates of these two species of Enterococcus. Results of 16S rRNA gene sequencing, sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of whole-cell protein profiles, and DNA-DNA reassociation experiments indicated that the blood isolate ATCC BAA-780 (SS 1728; CDC PNS-E1) corresponds to Enterococcus italicus, whose species epithet was proposed to designate isolates from artisanal Italian cheese. Strain ATCC BAA-781 (CCUG 47861; SS 1729; CDC PNS-E2), a vancomycin-resistant isolate recovered from the blood of a patient in the United States, was found to be highly related at the species level to another blood isolate (SS 1743; CCUG 47884) from Sweden, and for these we propose the designation Enterococcus sanguinicola sp. nov.

Prokaryotic microbiota of recycled paper mills with low or zero effluent

The tendency in the paper industry is to close all water loops to save water. This leads to higher process temperatures and may increase the colloidal and dissolved material in the process circulation. Increase of nutrients in the water circuits may favor microbiological growth and fouling. In this paper the chemical and microbial compositions of water circuits and deposits were studied of two closed cycled paper/board mills, one mill totally closed (0 m(3) waste water t(-1)), and the other low discharging (about 4 m(3 )t(-1)). The zero discharge mill accumulated high amounts (>10 g C L(-1)) of organic carbon in the circulation waters, about 40% of which composed of volatile acids (lactic, acetic, propionic and butyric acid). Water contents of sulfate, chloride, sodium and calcium increased to >1 g L(-1) of each. q-PCR targeted on 16S rRNA genes indicated that the bacteria in water circuits were mainly viable cells. In both mills anaerobic growth (10(6)-10(8) CFU mL(-1)) equalled or exceeded aerobic growth, with odor problem but no actual slime problem. The major part (40%) of all identifiable bacterial sequences were closest but yet distant (<96%) to Enterococcus cecorum and in the 4 m(3 )t(-1) discharging mill also Bacillus thermoamylovorans and Bacillus coagulans. Slimes and deposits from the mills contained high amounts, > or =10(8) g(-1), of archaean, but only the genus Methanothrix was identifiable from the cloned sequences. The findings indicate that closing the water circuits strongly limited diversity of the microbiota but allowed efficient mineralization of the dissolved and suspended matter.

A survey on biotechnological potential and safety of the novel Enterococcus species of dairy origin, E. italicus

The biotechnological and safety properties of the novel enterococcal species of dairy origin, Enterococcus italicus, were investigated. The strains of the species showed technological characteristics related to their use as adjunct cultures in the production of artisanal cheeses. They were susceptible or poorly resistant to several clinical relevant antibiotics. Moreover, E. italicus strains were associated with low virulence profiles, as verified by screening for the presence of 33 different genes encoding antibiotic resistance and known virulence factors in the genus Enterococcus. From the data obtained, we deduce that the presence of E. italicus strains in cheeses results in a low health risk and that within the species new safe adjunct cultures for the dairy industry could be found.

Incidence of antibiotic resistance and virulence determinants among Enterococcus italicus isolates from dairy products

The main objective of this work was to investigate the biosafety of Enterococcus italicus, a recently described enterococcal species widely diffused in dairy products. For this purpose, the antibiotic susceptibility and the incidence of virulence factors among 30 E. italicus isolates originating mainly from different Italian cheeses were tested. Although not all 30 isolates showed unique genotypes, PCR fingerprinting evidenced a notable genotypic diversity among the E. italicus collection under study. All isolates were susceptible to vancomycin, gentamicin, erythromycin, ampicillin, chloramphenicol and bacitracin. Five isolates corresponding to three unique genotypes exhibited phenotypic resistance to tetracycline with MICs ranging from 64-256mug/ml. By PCR-based detection, the genetic basis of the Tet(R) phenotype in these strains was linked to the tet(S) gene whereas detection of tet(L) and tet(M) genes and the integrase element int of the Tn916/Tn1545 family of transposons were negative. Likewise, none of the strains appeared to contain any of the tested virulence genes gelE, asaI, cpd, agg, cylA, cylB, cylM, ace and hyl(Efm). The results of this study warrant further research into the environmental dissemination of Tet(R)E. italicus and into the potential transferability of its tet(S) genes.

Enterococcus camelliae sp. nov., isolated from fermented tea leaves in Thailand

A Gram-positive and catalase-negative coccus that formed chains, strain FP15-1T, isolated from fermented tea leaves (‘miang’), was studied systematically. The strain was facultatively anaerobic and producedl-lactic acid from glucose. Demethylmenaquinone (DMK-7) was the major menaquinone. Straight-chain unsaturated fatty acids C16 : 1and C18 : 1were the dominant components. The DNA G+C content was 37.8 mol%. On the basis of 16S rRNA and RNA polymeraseαsubunit (rpoA) gene sequence analysis, strain FP15-1Twas closely related toEnterococcus italicusKCTC 5373T, with 99.2 and 93.8 % similarity, respectively. The strain could be clearly distinguished fromE. italicusATCC 5373Tby low DNA–DNA relatedness (≤33.8 %) and phenotypic characteristics. Therefore, this strain represent a novel species of the genusEnterococcus, for which the nameEnterococcus camelliaesp. nov. is proposed. The type strain is FP15-1T(=KCTC 13133T=NBRC 101868T=NRIC 0105T=TISTR 932T=PCU 277T).

Rapid identification of Enterococcus italicus by PCR with primers targeted to 16S rRNA gene

AIMS

To develop a species-specific PCR assay with primers targeted to 16S rRNA gene for the identification of Enterococcus italicus, a new species of Enterococcus, involved in the production of Italian cheeses.

METHODS AND RESULTS

The type strain of E. italicus (DSM 15952(T) - 16S rRNA gene accession no. AJ582753) and other strains of the species were subjected to a rapid identification by PCR using primer pairs located within the 16S rRNA gene. A species-specific PCR product of approximately 323 bp was obtained after amplification of all E. italicus strains tested. The specificity of the primers was validated with representatives of the most closely related genera and species and a number of other bacterial species. In addition, the technique enabled the recognition of E. italicus from cheeses.

CONCLUSIONS

The protocol was highly efficient and sensitive, enabling the identification of E. italicus from cheeses.

SIGNIFICANCE AND IMPACT OF THE STUDY

The species-specific PCR offers a reliable and rapid alternative to conventional phenotypic methods for the identification of E. italicus within the heterogeneous genus Enterococcus.

Vancomycin-susceptible dairy and clinical enterococcal isolates carry vanA and vanB genes

A total of 109 enterococcal isolates from dairy food products and from human and dog infections, isolated in Portugal, and 26 type and reference strains of the genus Enterococcus were screened for vancomycin resistance. MIC values, both for vancomycin and teicoplanin, were determined. The genetic relatedness of isolates carrying either vanA and/or vanB was determined using Pulsed Field Gel Electrophoresis. For vanA carrying isolates, transposon Tn1546 was partially mapped using PCR. None of the 59 dairy isolates was resistant to vancomycin. Among the 50 clinical isolates, only one, carrying vanB, behaved as resistant, with a MIC value of 256 microg/mL. The type and reference strains used were susceptible both to vancomycin and teicoplanin. vanA was found in 37% of the dairy isolates and 40% of the clinical isolates. vanB was only detected in 18% of the clinical, both human and dog, isolates. PCR partial mapping of Tn1546 revealed 23 different patterns among 42 isolates. Some patterns were shared between dairy and clinical isolates. Using Pulsed Field Gel Electrophoresis six groups of isolates were found to be genetically undistinguishable and grouping was found to be geographically and location specific/related. No genetic relatedness was found between isolates from dairy, human and veterinary sources. These results show that an incomplete and/or unfunctional Tn1546 element may explain the absence of resistant behaviour in the studied isolates, even when vanA gene is present. Moreover, the work reported shows that both clinical (human and animal) and dairy isolates have been in contact with VanA genotype of resistance and suggest that dissemination of vanA gene has been through transposable elements, like Tn1546, and not by clonal dissemination of a resistant strain. Therefore, a national strategy should be implemented to survey both vancomycin resistance and its genetic dissemination.

Reclassification of Enterococcus flavescens Pompei et al. 1992 as a later synonym of Enterococcus casseliflavus (ex Vaughan et al. 1979) Collins et al. 1984 and Enterococcus saccharominimus Vancanneyt et al. 2004 as a later synonym of Enterococcus italicus Fortina et al. 2004

The taxonomic relatedness between the speciesEnterococcus casseliflavusandEnterococcus flavescensand betweenEnterococcus italicusandEnterococcus saccharominimuswas investigated. Literature data had already indicated the synonymy betweenE. casseliflavusandE. flavescens, but this observation had not been formally published. Additional evidence that the two taxa represent a single species was provided by comparison of the partial sequences for three housekeeping genes, phenylalanyl-tRNA synthase alpha subunit (pheS), RNA polymerase alpha subunit (rpoA) and the alpha subunit of ATP synthase (atpA). Additional genomic data derived from DNA–DNA hybridization demonstrated that the two species are synonymous. ForE. italicusandE. saccharominimus, two recently described taxa, a high 16S rRNA gene sequence similarity of >99 % and analogous phenotypic features indicated a close taxonomic relatedness. The same multilocus sequence analysis scheme for the three housekeeping genes was also applied forE. italicusandE. saccharominimusand indicated possible conspecificity, an observation that was also confirmed by a high DNA–DNA hybridization value (⩾78 %). Data from the present study led to the proposal thatE. flavescensshould be reclassified as a later synonym ofE. casseliflavusand thatE. saccharominimusshould be reclassified as a later synonym ofE. italicus.

Enterococcus aquimarinus sp. nov., isolated from sea water

Two enterococcal strains LMG 16607(T) and LMG 16612 originating from sea water were analysed in a polyphasic taxonomic study. Both strains, assigned as Enterococcus sp. in the BCCM/LMG culture collection, possessed analogous protein profiles, but these were different from all other enterococcal species. 16S rRNA gene sequence analysis of one strain showed the highest similarity, 96.9-96.1%, with its closest phylogenetic neighbours Enterococcus saccharolyticus, Enterococcus sulfureus, Enterococcus saccharominimus and Enterococcus italicus. Further genomic analysis by (GTG)(5)-PCR fingerprinting and sequence analysis of the housekeeping gene phenylalanyl-tRNA synthase (pheS) and distinct biochemical features confirmed that the two strains represent a novel enterococcal species for which the name Enterococcus aquimarinus sp. nov. is proposed. The type strain is LMG 16607(T) (=CCM 7283(T)).

Phylogeny and identification of Enterococci by atpA gene sequence analysis

The relatedness among 91 Enterococcus strains representing all validly described species was investigated by comparing a 1,102-bp fragment of atpA, the gene encoding the alpha subunit of ATP synthase. The relationships observed were in agreement with the phylogeny inferred from 16S rRNA gene sequence analysis. However, atpA gene sequences were much more discriminatory than 16S rRNA for species differentiation. All species were differentiated on the basis of atpA sequences with, at a maximum, 92% similarity. Six members of the Enterococcus faecium species group (E. faecium, E. hirae, E. durans, E. villorum, E. mundtii, and E. ratti) showed > 99% 16S rRNA gene sequence similarity, but the highest value of atpA gene sequence similarity was only 89.9%. The intraspecies atpA sequence similarities for all species except E. faecium strains varied from 98.6 to 100%; the E. faecium strains had a lower atpA sequence similarity of 96.3%. Our data clearly show that atpA provides an alternative tool for the phylogenetic study and identification of enterococci.

Application of multilocus sequence analysis (MLSA) for rapid identification of Enterococcus species based on rpoA and pheS genes

The aim of this study was to evaluate the use of RNA polymeraseαsubunit (rpoA) and phenylalanyl-tRNA synthase (pheS) gene sequences as species identification tools for enterococci. Ninety-six representative strains comprising all currently recognizedEnterococcusspecies were examined.rpoAgene sequences generated a robust classification into species groups similar to the one based on 16S rRNA gene sequence analysis. On the other hand, thepheSgene is a fast-evolving clock even better suited for species delineation than therpoAgene, but not for recognition of species groups withinEnterococcusas determined by bothrpoAand 16S rRNA genes. All enterococcal species were clearly differentiated on the basis of theirrpoAandpheSsequences. Evaluation of intraspecies variation showed that bothrpoAandpheSgenes have a high degree of homogeneity among strains of the same species. Strains of the same enterococcal species have at least 99 %rpoAand 97 %pheSgene sequence similarity, whereas, different enterococcal species have at maximum 97 %rpoAand 86 %pheSgene sequence similarity. It was concluded that both genes can be used as reliable tools for identification of clinical and environmental species ofEnterococcusand are efficient screening methods for the detection of novel species. The sequence data obtained in this study were compared to the availableatpAand 16S rRNA gene sequences. The MLSA approach toEnterococcustaxonomy provides portable, highly reproducible data with lower costs for rapid identification of all enterococcal species.