The ecology of the streptococci

The wild solitary bees Andrena vaga, Anthophora plumipes, Colletes cunicularius, and Osmia cornuta microbiota are host specific and dominated by endosymbionts and environmental microorganisms

We characterized the microbial communities of the crop, midgut, hindgut, and ovaries of the wild solitary bees Andrena vaga, Anthophora plumipes, Colletes cunicularius, and Osmia cornuta through 16S rRNA gene and ITS2 amplicon sequencing and a large-scale isolation campaign. The bacterial communities of these bees were dominated by endosymbionts of the genera Wolbachia and Spiroplasma. Bacterial and yeast genera representing the remaining predominant taxa were linked to an environmental origin. While only a single sampling site was examined for Andrena vaga, Anthophora plumipes, and Colletes cunicularius, and two sampling sites for Osmia cornuta, the microbiota appeared to be host specific: bacterial, but not fungal, communities generally differed between the analyzed bee species, gut compartments and ovaries. This may suggest a selective process determined by floral and host traits. Many of the gut symbionts identified in the present study are characterized by metabolic versatility. Whether they exert similar functionalities within the bee gut and thus functional redundancy remains to be elucidated.

Impact of transgenerational host switch on gut bacterial assemblage in generalist pest, Spodoptera littoralis (Lepidoptera: Noctuidae)

Diet composition is vital in shaping gut microbial assemblage in many insects. Minimal knowledge is available about the influence of transgenerational diet transition on gut microbial community structure and function in polyphagous pests. This study investigated transgenerational diet-induced changes in Spodoptera littoralis larval gut bacteriome using 16S ribosomal sequencing. Our data revealed that 88% of bacterial populations in the S. littoralis larval gut comprise Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes. The first diet transition experiment from an artificial diet (F0) to a plant diet (F1), cabbage and cotton, caused an alteration of bacterial communities in the S. littoralis larval gut. The second transgenerational diet switch, where F1 larvae feed on the same plant in the F2 generation, displayed a significant variation suggesting further restructuring of the microbial communities in the Spodoptera larval gut. F1 larvae were also challenged with the plant diet transition at the F2 generation (cabbage to cotton or cotton to cabbage). After feeding on different plant diets, the microbial assemblage of F2 larvae pointed to considerable differences from other F2 larvae that continued on the same diet. Our results showed that S. littoralis larval gut bacteriome responds rapidly and inexplicably to different diet changes. Further experiments must be conducted to determine the developmental and ecological consequences of such changes. Nevertheless, this study improves our perception of the impact of transgenerational diet switches on the resident gut bacteriome in S. littoralis larvae and could facilitate future research to understand the importance of symbiosis in lepidopteran generalists better.

Sequencing to identify pathogens in Tenebrio molitor: Implications in insects farmed for food and feed

Introduction

The farmed insect industry is increasing in number and size to meet the demand for sustainably-produced protein. Larger insect farms are prone to losses due to pathogens, and more information is needed regarding the health of insects reared for food and feed.

Methods

In this study, high throughput sequencing was used to identify potential pathogens in a colony of Tenebrio molitor (yellow mealworm, Coleoptera: Tenebrionidae) that exhibited increased mortality in immature stages with eventual colony collapse. Sequences also were obtained from a healthy new colony of T. molitor, as well as a recovered individual from the collapsed colony.

Results

Screening of sequences obtained from the colonies and their rearing diet indicated that the collapsed colony had low diversity in microbial taxa, with predominantly sequences from the families Staphylococcaeceae and Streptococcaceae constituting from 53 to 88% of the total microbial reads. Conversely, in the new colony and their rearing diet, microbial sequences were from more than 15 different taxa, with Lactobacilleceae the most prevalent but representing only 21% of the total microbial reads. Evidence indicates that Bacillus thuringiensis may have been involved in the collapse of the colony, leading to sepsis and microbial dysbiosis, although the source of the bacteria was not identified. Sequences from the recovered individual reflected a microbial flora profile that was intermediate between those of the diseased collapsed and new colonies.

Discussion

These findings have implications for insects reared in confined environments and provide a rapid method to screen insect colonies by sequencing healthy and potentially diseased individuals.

Prospective bacterial and fungal sources of hyaluronic acid: A review

The unique biological and rheological properties make hyaluronic acid a sought-after material for medicine and cosmetology. Due to very high purity requirements for hyaluronic acid in medical applications, the profitability of streptococcal fermentation is reduced. Production of hyaluronic acid by recombinant systems is considered a promising alternative. Variations in combinations of expressed genes and fermentation conditions alter the yield and molecular weight of produced hyaluronic acid. This review is devoted to the current state of hyaluronic acid production by recombinant bacterial and fungal organisms.

Distribution of two-component signal transduction systems BlpRH and ComDE across streptococcal species

Two-component signal transduction (TCS) systems are important regulatory pathways in streptococci. A typical TCS encodes a membrane-anchored sensor kinase (SK) and a cytoplasmic response regulator (RR). Approximately, 20 different types of TCSs are encoded by various streptococci. Among them, two TCSs, in particular BlpRH and ComDE, are required for bacteriocins production and competence development. The SK component of these two TCSs is highly similar and belongs to the protein kinase-10 (HPK-10) subfamily. While these two TCSs are present in streptococci, no systematic studies have been done to differentiate between these two TCSs, and the existence of these pathways in several species of the genus Streptococcus is also unknown. The lack of information about these pathways misguided researchers for decades into believing that the Streptococcus mutans BlpRH system is a ComDE system. Here, we have attempted to distinguish between the BlpRH and ComDE systems based on the location of the chromosome, genomic arrangement, and conserved residues. Using the SyntTax and NCBI databases, we investigated the presence of both TCS systems in the genome of several streptococcal species. We noticed that the NCBI database did not have proper annotations for these pathways in several species, and many of them were wrongly annotated, such as CitS or DpiB instead of BlpH. Nevertheless, our critical analyses led us to classify streptococci into two groups: class A (only the BlpRH system) and class B (both the BlpRH and ComDE systems). Most of the streptococcal groups, including bovis, pyogenic, mutans, salivarius, and suis, encode only the BlpRH system. In contrast, only in the mitis and anginosus groups were both the TCS systems present. The focus of this review is to identify and differentiate between the BlpRH and ComDE systems, and discuss these two pathways in various streptococci.

Streptococcus dysgalactiae subspecies dysgalactiae in Norwegian bovine dairy herds: Risk factors, sources, and genomic diversity

Despite the importance of Streptococcus dysgalactiae ssp. dysgalactiae (SDSD) as an udder pathogen, the reservoir and epidemiological characteristics of this bacterium are largely unexplored. The aims of this study were to investigate risk factors for SDSD intramammary infections (SDSD-IMI) in Norwegian bovine dairy herds, identify sources of SDSD on animals and in the environment, and elucidate the genetic diversity of SDSD isolates. Data from herd recordings and a questionnaire were used to investigate herd-level risk factors for SDSD-IMI in 359 freestall dairy herds. Seven herds with a suspected high prevalence of SDSD-IMI were visited to sample extramammary sources (e.g., skin, wounds, mucous membranes, and freestall environment). Bacterial isolates were whole-genome sequenced to investigate the distribution of SDSD genotypes within herds and to assess the phylogenetic relationship between SDSD isolates from 27 herds across Norway. Risk factors for high incidence of SDSD-IMI in freestall dairy herds were related to housing, including closed flooring in alleys and rubber mats in cubicle bases. Parlor milking was also a risk factor compared with automatic milking systems. From herd visits, a considerable proportion of extramammary samples were SDSD positive, particularly from wounds and skin of the animals and the cubicle bases. Samples from mucous surfaces (nostrils, rectum, and vagina) and water troughs were least frequently positive. Eight multilocus sequence types (ST) were identified among the sequenced isolates from 27 herds, and phylogenetic analyses revealed 8 clades corresponding to ST. No significant association was identified between sampling site (milk, body sites, and environment) and ST. In 4 of 6 herds from which 5 or more isolates were available, one ST dominated and was found in milk and extramammary samples. One ST (ST453) was found in 15 of 27 herds, which implies that this is a widely distributed and possibly a bovine-adapted strain. Findings in this study suggest that SDSD is a cow-adapted opportunist with potential for contagious transmission, and that the freestall environment is likely to play a role in transmission between cows.

Streptococcus gordonii: Pathogenesis and Host Response to Its Cell Wall Components

Streptococcus gordonii, a Gram-positive bacterium, is a commensal bacterium that is commonly found in the skin, oral cavity, and intestine. It is also known as an opportunistic pathogen that can cause local or systemic diseases, such as apical periodontitis and infective endocarditis. S. gordonii, an early colonizer, easily attaches to host tissues, including tooth surfaces and heart valves, forming biofilms. S. gordonii penetrates into root canals and blood streams, subsequently interacting with various host immune and non-immune cells. The cell wall components of S. gordonii, which include lipoteichoic acids, lipoproteins, serine-rich repeat adhesins, peptidoglycans, and cell wall proteins, are recognizable by individual host receptors. They are involved in virulence and immunoregulatory processes causing host inflammatory responses. Therefore, S.gordonii cell wall components act as virulence factors that often progressively develop diseases through overwhelming host responses. This review provides an overview of S. gordonii, and how its cell wall components could contribute to the pathogenesis and development of therapeutic strategies.

Expanding the Vocabulary of Peptide Signals in Streptococcus mutans

Streptococci, including the dental pathogen Streptococcus mutans, undergo cell-to-cell signaling that is mediated by small peptides to control critical physiological functions such as adaptation to the environment, control of subpopulation behaviors and regulation of virulence factors. One such model pathway is the regulation of genetic competence, controlled by the ComRS signaling system and the peptide XIP. However, recent research in the characterization of this pathway has uncovered novel operons and peptides that are intertwined into its regulation. These discoveries, such as cell lysis playing a critical role in XIP release and importance of bacterial self-sensing during the signaling process, have caused us to reevaluate previous paradigms and shift our views on the true purpose of these signaling systems. The finding of new peptides such as the ComRS inhibitor XrpA and the peptides of the RcrRPQ operon also suggests there may be more peptides hidden in the genomes of streptococci that could play critical roles in the physiology of these organisms. In this review, we summarize the recent findings in S. mutans regarding the integration of other circuits into the ComRS signaling pathway, the true mode of XIP export, and how the RcrRPQ operon controls competence activation. We also look at how new technologies can be used to re-annotate the genome to find new open reading frames that encode peptide signals. Together, this summary of research will allow us to reconsider how we perceive these systems to behave and lead us to expand our vocabulary of peptide signals within the genus Streptococcus.

Identification of Putative Novel Class-I Lanthipeptides in Firmicutes: A Combinatorial In Silico Analysis Approach Performed on Genome Sequenced Bacteria and a Close Inspection of Z-Geobacillin Lanthipeptide Biosynthesis Gene Cluster of the Thermophilic Geobacillus sp. Strain ZGt-1

Lanthipeptides are ribosomally synthesized and post-translationally modified polycyclic peptides. Lanthipeptides that have antimicrobial activity are known as lantibiotics. Accordingly, the discovery of novel lantibiotics constitutes a possible solution for the problem of antibiotic resistance. We utilized the publicly available genome sequences and the bioinformatic tools tailored for the detection of lanthipeptides. We designed our strategy for screening of 252 firmicute genomes and detecting class-I lanthipeptide-coding gene clusters. The designed strategy resulted in identifying 69 class-I lanthipeptide sequences, of which more than 10% were putative novel. The identified putative novel lanthipeptides have not been annotated on the original or the RefSeq genomes, or have been annotated merely as coding for hypothetical proteins. Additionally, we identified bacterial strains that have not been previously recognized as lanthipeptide-producers. Moreover, we suggest corrections for certain firmicute genome annotations, and recommend lanthipeptide records for enriching the bacteriocin genome mining tool (BAGEL) databases. Furthermore, we propose Z-geobacillin, a putative class-I lanthipeptide coded on the genome of the thermophilic strain Geobacillus sp. ZGt-1. We provide lists of putative novel lanthipeptide sequences and of the previously unrecognized lanthipeptide-producing bacterial strains, so they can be prioritized for experimental investigation. Our results are expected to benefit researchers interested in the in vitro production of lanthipeptides.

Antimicrobial resistance of Enterococcus species from meat and fermented meat products isolated by a PCR-based rapid screening method

Enterococci are predominantly found in the gastrointestinal tract of humans and animals, but species commonly resident on vegetation are known. Their presence in large numbers in foods may indicate a lapse in sanitation and their ability to serve as a genetic reservoir of transferable antibiotic resistance is of concern. Conventional culture methods for identification of enterococci are slow and sometimes give false results because of the biochemical diversity of the organisms in this genus. This work reports the development of a PCR-based assay to detect enterococci at the genus level by targeting a 16S rRNA sequence. Published 16S rRNA sequences were aligned and used to design genus specific primers (EntF and EntR). The primers were able to amplify a 678 bp target region from Enterococcus faecalis ATCC 7080 and 20 other strains of enterococci from 11 different species, but there was no amplification by 32 species from closely related genera (Pediococcus, Lactobacillus, Streptococcus and Listeria) or species of Escherichia coli and Salmonella. The PCR positive samples were plated, screened by a colony patch technique and their identities were confirmed by API 20 Strep panels and sequencing. When dry fermented sausage and ham as well as fresh meat batter for dry cured sausage manufacture were tested for enterococci by the method, 29 Enterococcus strains (15 E. faecalis, 13 E. faecium, and one E. gallinarum) were identified. When susceptibility of these enterococci to 12 antibiotics was tested, the highest incidence of resistance was to clindamycin (89.6%), followed by tetracycline hydrochloride (65.5%), tylosin (62%), erythromycin (45%), streptomycin and neomycin (17%), chloramphenicol (10.3%), penicillin (10.3%), ciprofloxacin (10.3%) and gentamicin (3.4%). None was resistant to the clinically important drugs vancomycin or ampicillin. Most strains (27/29) were resistant to more than one antibiotic while 17 of 29 strains were resistant to three to 8 antibiotics. The molecular method developed was validated for speciation of enterococci and was useful in assessing uncooked processed meat products as a reservoir for multi-drug resistant Enterococcus species.

Microbial communities associated with wet flue gas desulfurization systems

Flue gas desulfurization (FGD) systems are employed to remove SO(x) gasses that are produced by the combustion of coal for electric power generation, and consequently limit acid rain associated with these activities. Wet FGDs represent a physicochemically extreme environment due to the high operating temperatures and total dissolved solids (TDS) of fluids in the interior of the FGD units. Despite the potential importance of microbial activities in the performance and operation of FGD systems, the microbial communities associated with them have not been evaluated. Microbial communities associated with distinct process points of FGD systems at several coal-fired electricity generation facilities were evaluated using culture-dependent and -independent approaches. Due to the high solute concentrations and temperatures in the FGD absorber units, culturable halothermophilic/tolerant bacteria were more abundant in samples collected from within the absorber units than in samples collected from the makeup waters that are used to replenish fluids inside the absorber units. Evaluation of bacterial 16S rRNA genes recovered from scale deposits on the walls of absorber units revealed that the microbial communities associated with these deposits are primarily composed of thermophilic bacterial lineages. These findings suggest that unique microbial communities develop in FGD systems in response to physicochemical characteristics of the different process points within the systems. The activities of the thermophilic microbial communities that develop within scale deposits could play a role in the corrosion of steel structures in FGD systems.

Intraguild predation provides a selection mechanism for bacterial antagonistic compounds

Bacteriocins are bacterial proteinaceous toxins with bacteriostatic or bacteriocidal activity towards other bacteria. The current theory on their biological role concerns especially colicins, with underlying social interactions described as an example of spite. This leads to a rock-paper-scissors game between colicin producers and sensitive and resistant variants. The generality of this type of selection mechanism has previously been challenged with lactic acid bacterial (LAB) bacteriocins as an example. In the natural environment of LAB, batch cultures are the norm opposed to the natural habitats of Escherichia coli where continuous cultures are prevailing. This implies that fitness for LAB, to a large degree, is related to survival rates (bottleneck situations) rather than to growth rates. We suggest that the biological role of LAB bacteriocins is to enhance survival in the stationary growth phase by securing a supply of nutrients from lysed target cells. Thus, this social interaction is an example of selfishness rather than of spite. Specifically, it fits into an ecological model known as intraguild predation (IGP), which is a combination of competition and predation where the predator (LAB bacteriocin producer) and prey (bacteriocin susceptible bacteria) share similar and often limited resources. We hypothesize that IGP may be a common phenomenon promoting microbial production of antagonistic compounds.

Cloning and comparison of phylogenetically related chitinases from Listeria monocytogenes EGD and Enterococcus faecalis V583

AIMS

To compare enzymatic activities of two related chitinases, ChiA and EF0361, encoded by Listeria monocytogenes and Enterococcus faecalis, respectively.

METHODS AND RESULTS

The chiA and EF0361 genes were amplified by PCR, cloned and expressed with histidine tags, allowing easy purification of the gene products. ChiA had a molecular weight as predicted from the amino acid sequence, whereas EF0361 was 1840 Da lower than expected because of C-terminal truncation. The ChiA and EF0361 enzymes showed activity towards 4-nitrophenyl N,N'-diacetyl-beta-D-chitobioside with K(m) values of 1.6 and 2.1 mmol l(-1), respectively, and k(cat) values of 21.6 and 6.5 s(-1). The enzymes also showed activity towards 4-nitrophenyl beta-D-N, N', N''-triacetylchitotriose and carboxy-methyl-chitin-Remazol Brilliant Violet but not towards 4-nitrophenyl N-acetyl-beta-D-glucosaminide. Chitinolytic specificities of the enzymes were supported by their inactivity towards the substrates 4-nitrophenyl beta-D-cellobioside and peptidoglycan. The pH and temperature profiles for catalytic activities were relatively similar for both the enzymes.

CONCLUSION

The ChiA and EF0361 enzymes show a high degree of similarity in their catalytic activities although their hosts share environmental preferences only to some extent.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study contributes to an understanding of the chitinolytic activities by L. monocytogenes and Ent. faecalis. Detailed information on their chitinolytic systems will help define potential reservoirs in the natural environment and possible transmission routes into food-manufacturing plants.

Characterization of wild strains ofLactococcus lactissubsp.lactisisolated from Cabrales cheese

TwentyLactococcus lactissubsp.lactisstrains isolated from cheese made from raw milk have been, studied and compared with well known starter strains. Many of them produced acid bacteriocins resembling those of other lactic streptococci and their patterns of antimicrobial agent susceptibility were also similar to previously studied dairy strains. On the basis of their ability to clot milk they could be divided into two groups. Some strains were rapid fermenters, with highβ-phosphogalactosidase and proteolytic activities. The other group had lowβ-phosphogalactosidase activity and coagulated milk slowly, but seemed to have proteolytic activity. All the strains had plasmid DNA in amounts and sizes similar to starter strains. Aβ-phosphogalactosidase probe was constructed with plasmid DNA from aLc. lactissubsp.lactisNCDO 712 derivative. Southern hybridization located homologous sequences in chromosomal and plasmid DNA from the wild isolates that fermented lactose efficiently, but the degree of homology was lower than that observed between starter strains.

Microbial transport: Adaptations to natural environments

The cytoplasmic membrane of bacteria is the matrix for metabolic energy transducing processes such as proton motive force generation and solute transport. Passive permeation of protons across the cytoplasmic membrane is a crucial determinant in the proton motive generating capacity of the organisms. Adaptations of the membrane composition are needed to restrict the proton permeation rates especially at higher temperatures. Thermophilic bacteria cannot sufficiently restrict this proton permeation at their growth temperature and have to rely on the much lower permeation of Na + to generate a sodium motive force for driving metabolic energy-dependent membrane processes. Specific transport systems mediate passage across the membrane at physiological rates of all compounds needed for growth and metabolism and of all end products of metabolism. Some of transport systems, the secondary transporters, transduce one form of electrochemical energy into another form. These transporters can play crucial roles in the generation of metabolic energy. This is especially so in anaerobes such as Lactic Acid Bacteria which live under energy-limited conditions. Several transport systems are specifically aimed at the generation of metabolic energy during periods of energy-limitation. In their natural environment bacteria are also often exposed to cytotoxic compounds, including antibiotics. Many bacteria can respond to this live-threatening condition by overexpressing powerful drug-extruding multidrug resistance systems.

Control of Staphylococcus aureus in sausages by enterocin AS-48

Results presented here are the first contribution on the anti-staphylococcal activity of bacteriocin AS-48 in a model meat sausage system. We have examined bacteriocin application, by inoculation with the enterocin AS-48 producer strain Enterococcus faecalis A-48-32 or by adding a semi-purified bacteriocin preparation. AS-48 inhibits proliferation of Staphylococcus aureus in sausages when added at concentrations of 30 or 40μg/g, achieving a significant reduction of 2 and 5.31 log units, respectively, in viable counts (CFU/g) of staphylococci with respect to the untreated control. The presence of bacteriocin also had a moderate negative effect on total lactic acid bacteria. AS-48(+) strain was developed well in the meat mixture, producing sufficient amounts of AS-48 (to a maximum of 76-88 arbitrary units/g) to control growth of staphylococci. The best result was achieved with a bacteriocinogenic strain inoculum of 10(7)CFU/g.

Identification of plant-associated enterococci

AIMS

Enterococcus isolates from forage grass were subjected to taxonomical investigations and tested for antibiotic resistance.

METHODS AND RESULTS

The identification procedure included phenotypic characterizations, restriction analyses of polymerase chain reaction-amplified 16S rDNA, whole-cell protein profile analyses and 16S rDNA sequence analyses. Agar diffusion tests were performed to detect antibiotic resistance.

CONCLUSION

The isolates were identified as belonging to the species Enterococcus faecium, Ent. mundtii, Ent. casseliflavus, Ent. faecalis and Ent. sulfureus. However, the majority of isolates differed distinctly in their restriction patterns from those of known species. They formed a group of a homogeneous 16S rDNA genotype (VI). The 16S rDNA sequence of a representative isolate revealed the closest relationship to the species Ent. faecalis (similarity of 97.4%). All isolates were sensitive to vancomycin, but almost all were resistant to gentamycin and streptomycin.

SIGNIFICANCE AND IMPACT OF THE STUDY

The taxonomical investigations suggest that the isolates of the 16S rDNA genotype VI represent a new plant-associated Enterococcus species.

Population dynamics and antagonistic potential of enterococci colonizing the phyllosphere of grasses

AIMS

To investigate the spatial and temporal dynamics of enterococci colonizing forage grass and their ability to produce bacteriocins.

METHODS AND RESULTS

Enterococci could be detected on above-ground plant parts throughout the growing season, with high continuity but low cell numbers (2.60 x 101-6.16 x 104 cfu g-1 fresh matter). A total of 750 strains were isolated and identified by their whole-cell protein patterns as Enterococcus faecalis (7.9%), Ent. mundtii (7.9%), Ent. casseliflavus (5.5%), Ent. faecium (5.2%) and Ent. sulfureus (0.1%). The vast majority of the strains (69.7%) formed a homogeneous 16S rDNA genotype that differed from those of known enterococci. A screening for antagonistic activity using an agar spot test revealed that 18.4% of all isolates were potential antagonists. Partially-purified proteins extracted from cell-free culture supernatant fluids of various species were characterized as pH- and heat-stable bacteriocins active against a wide range of lactic acid bacteria, clostridia and Listeria. The producing strains were antagonistically active even on 'phylloplane agar' at temperatures between 4 and 37 degrees C.

CONCLUSION

Enterococci are a common part of the epiphytic microflora of grasses, displaying probably some antagonistic activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results provide new information on the distribution, species diversity and antagonistic potential of enterococci in the phyllosphere.

Bacterial flora in the gut ofHelix aspersa(Gastropoda Pulmonata): evidence for a permanent population with a dominant homolactic intestinal bacterium,Enterococcus casseliflavus

We previously demonstrated the existence of bacteria degrading carboxy-methyl-cellulose in the gut of the phytophagous snail Helix aspersa and found Enterobacteriaceae predominating in the intestine of snails dissected in aerobic conditions. Here, we investigated the effects of several nutritional treatments on the snail's microflora. Food sterilization led to increased snail growth and reduced cellulase activity in the crop, suggesting a noxious effect of microbial exogenous cellulases. A second aim of this study was to look for anaerobic bacteria. No strict anaerobic cellulolytic, homoacetogenic, or methanogenic bacteria were enriched from the gut. However, a motile Gram-positive homolactic coccobacillus, grown in anaerobic conditions, dominated in the snail's intestine (1.57 x 109± 0.10 x 109cells.g-1intestine). It was identified as Enterococcus casseliflavus. Its occurrence in the intestine of H. aspersa is discussed with regard to the snail's digestive processes and the presence of a fecal mucous ribbon. A possible snail-bacterium synergistic action is suggested.Key words: snail, Helix aspersa, gut, Enterococcus casseliflavus, fermentative homolactic bacterium, antibiotics.

Identification and characterization of proteolytic activity of Enterococcus spp. isolated from milk and Roncal and Idiazábal cheese

Roncal and Idiazábal cheeses are manufactured from ewe's milk in the Autonomous Region of Navarre in Spain. Levels of enterococci are high in these cheeses and in other types of ewe's-milk cheeses. The present study has identified enterococci present in the milk used and in the Roncal and Idiazábal cheeses after 120 days of ripening. A total of 282 strains were isolated and identified, and the cytoplasmic and extracellular enzymatic activities of some of the strains were assessed. The dominating species were Enterococcus faecalis, which accounted for 85% of the total both in the milk as well as in the two types of cheese, and Enterococcus faecium, Enterococcus durans, and Enterococcus avium which were present in lower proportions. Aminopeptidase and proteinase activity levels in enterococci were low, and considerable variation between strains of the same species was recorded, highlighting the need to study individual strains when selecting the most suitable bacteria as a starter culture. Aminopeptidase activity levels for the enterococci were appreciably higher at pH 7 than at pH 5.5, hence aminopeptidase activity by enterococci would appear to be less significant in the normal manufacturing conditions of the two cheeses.

Culture media for non-sporulating gram-positive food spoilage bacteria

The spoilage association especially of protein-rich foods can be dominated by Gram-positive bacteria, notably lactic acid bacteria (LAB) which affect vacuum packaged refrigerated processed meats and some dairy products. New food ecosystems are being created by novel packaging and processing technologies, resulting in spoilage associations differing from those previously reported. In addition, improvement in identification methods, allow the detection and isolation of 'novel' bacterial groups, e.g., Carnobacterium spp. This review considers the genera Aerococcus, Brevibacterium, Brochothrix, Carnobacterium, Kurthia, Lactobacillus, Leuconostoc, Microbacterium, Micrococcus, Pediococcus and Propionibacterium. Strictly selective procedures, including incubation temperature and atmosphere, are not yet available for the genera Aerococcus, Brevibacterium, Microbacterium and Micrococcus, and only with some limitations for Kurthia and Propionibacterium. On the other hand, a causative role in food spoilage has not been established clearly for all those groups, some of which may be 'opportunistic' in their behaviour. The LAB groups Lactobacillus, Leuconostoc and Pediococcus ('LLP-Group') often share similar habitats and show similar physiological behaviour on a number of elective and selective media. Modifications to increase selectivity have been based mainly on de Man, Rogosa and Sharpe (MRS) or Rogosa agar, and include pH reduction, supplementation with chemical preservatives (e.g., sorbic acid and nitrate) and the use of reduced atmospheres or suboptimal incubation temperatures. Carnobacteria differ from other LAB in their non-aciduric nature, and selective plating procedures use high-pH media (pH 8-9) by which competitors (mainly lactobacilli) are eliminated.

Bioenergetics and solute transport in lactococci

During the last few years the studies about the physiology and bioenergetics of lactic acid bacteria during growth and starvation have evolved from a descriptive level to an analysis of the molecular events in the regulation of various processes. Considerable progress has been made in the understanding of the modes of metabolic energy generation, the mechanism of homeostasis of the internal pH, and the mechanism and regulatory processes of transport systems for sugars, amino acids, peptides, and ions. Detailed studies of these transport processes have been performed in cytoplasmic membrane vesicles of these organisms in which a foreign proton pump has been introduced to generate a high proton motive force.

Characterization of aerobic, facultative anaerobic, and anaerobic bacteria in an acidogenic phase reactor and their metabolite formation

Fifty-two aerobic and facultative anaerobic and 57 anaerobic bacterial isolates were obtained from an acidogenic phase digestion system. These isolates were characterized and the similarities between the different strains were calculated using Sokal and Michener's similarity coefficient. The aerobic and facultative anaerobic strains clustered in two major groups with the strains of the first main group being gram-negative fermentative rods, representing the generaKlebsiella, Enterobacter, Escherichia andAeromonas. Isolates of the second group were gram-positive streptococci similar toStreptococcus lactis. The strict anaerobic isolates also clustered into two main groups with strains of cluster A being identified as members of the genusFusobacterium while strains in cluster B were members of the genusBacteroides. Hypothetical mean organisms were calculated for each cluster and used in further culture studies. The major products of the continuously fed acidogenic phase reactor were ethanol and acetic, propionic, and butyric acids. In batch cultures, ethanol, acetic acid, diacetyl, and 2,3-butanediol were formed by the strains as major products both under aerobic and anaerobic conditions. The ability of the aerobic and facultative anaerobic strains to be metabolically active under anaerobic conditions indicates a prominent role in acidogenic reactors.