Cell-cell communication in food related bacteria

Gut-Brain Interactions and Their Impact on Astrocytes in the Context of Multiple Sclerosis and Beyond

Multiple Sclerosis (MS) is a chronic autoimmune inflammatory disease of the central nervous system (CNS) that leads to physical and cognitive impairment in young adults. The increasing prevalence of MS underscores the critical need for innovative therapeutic approaches. Recent advances in neuroimmunology have highlighted the significant role of the gut microbiome in MS pathology, unveiling distinct alterations in patients' gut microbiota. Dysbiosis not only impacts gut-intrinsic processes but also influences the production of bacterial metabolites and hormones, which can regulate processes in remote tissues, such as the CNS. Central to this paradigm is the gut-brain axis, a bidirectional communication network linking the gastrointestinal tract to the brain and spinal cord. Via specific routes, bacterial metabolites and hormones can influence CNS-resident cells and processes both directly and indirectly. Exploiting this axis, novel therapeutic interventions, including pro- and prebiotic treatments, have emerged as promising avenues with the aim of mitigating the severity of MS. This review delves into the complex interplay between the gut microbiome and the brain in the context of MS, summarizing current knowledge on the key signals of cross-organ crosstalk, routes of communication, and potential therapeutic relevance of the gut microbiome. Moreover, this review places particular emphasis on elucidating the influence of these interactions on astrocyte functions within the CNS, offering insights into their role in MS pathophysiology and potential therapeutic interventions.

Environmental processes and health implications potentially mediated by dust-borne bacteria

Understanding microbial migration and survival mechanisms in dust events (DEs) can elucidate genetic and metabolic exchange between environments and help predict the atmospheric pathways of ecological and health-related microbial stressors. Dust-borne microbial communities have been previously characterized, but the impact and interactions between potentially active bacteria within transported communities remain limited. Here, we analysed samples collected during DEs in Israel, using amplicon sequencing of the 16S rRNA genes and transcripts. Different air trajectories and wind speeds were associated not only with the genomic microbial community composition variations but also with specific 16S rRNA bacterial transcripts. Potentially active dust-borne bacteria exhibited positive interactions, including carbon and nitrogen cycling, biotransformation of heavy metals, degradation of organic compounds, biofilm formation, and the presence of pathogenic taxa. This study provides insights into the potential interactive relationships and survival strategies of microorganisms within the extreme dust environment.

Effect of LuxS/AI-2-mediated quorum sensing system on bacteriocin production of Lactobacillus plantarum NMD-17

Lactobacillus plantarum NMD-17 separated from koumiss could produce a bacteriocin named plantaricin MX against Gram-positive bacteria and Gram-negative bacteria. The bacteriocin synthesis of L. plantarum NMD-17 was remarkably induced in co-cultivation with Lactobacillus reuteri NMD-86 as the increase of cell numbers and AI-2 activity, and the expressions of luxS encoding signal AI-2 synthetase, plnB encoding histidine protein kinase, plnD encoding response regulator, and plnE and plnF encoding structural genes of bacteriocin were significantly upregulated in co-cultivation, showing that the bacteriocin synthesis of L. plantarum NMD-17 in co-cultivation may be regulated by LuxS/AI-2-mediated quorum sensing system. In order to further demonstrate the role of LuxS/AI-2-mediated quorum sensing system in the bacteriocin synthesis of L. plantarum NMD-17, plasmids pUC18 and pMD18-T simple were used as the skeleton to construct the suicide plasmids pUC18-UF-tet-DF and pMD18-T simple-plnB-tet-plnD for luxS and plnB-plnD gene deletion, respectively. luxS and plnB-plnD gene knockout mutants were successfully obtained by homologous recombination. luxS gene knockout mutant lost its AI-2 synthesis ability, suggesting that LuxS protein encoded by luxS gene is key enzyme for AI-2 synthesis. plnB-plnD gene knockout mutant lost the ability to synthesize bacteriocin against Salmonella typhimurium ATCC14028, indicating that plnB-plnD gene was a necessary gene for bacteriocin synthesis of L. plantarum NMD-17. Bacteriocin synthesis, cell numbers, and AI-2 activity of luxS or plnB-plnD gene knockout mutants in co-cultivation with L. reuteri NMD-86 were obviously lower than those of wild-type strain in co-cultivation at 6-9 h (P < 0.01). The results showed that LuxS/AI-2-mediated quorum sensing system played an important role in the bacteriocin synthesis of L. plantarum NMD-17 in co-cultivation.

Quorum sensing in human gut and food microbiomes: Significance and potential for therapeutic targeting

Human gut and food microbiomes interact during digestion. The outcome of these interactions influences the taxonomical composition and functional capacity of the resident human gut microbiome, with potential consequential impacts on health and disease. Microbe-microbe interactions between the resident and introduced microbiomes, which likely influence host colonisation, are orchestrated by environmental conditions, elements of the food matrix, host-associated factors as well as social cues from other microorganisms. Quorum sensing is one example of a social cue that allows bacterial communities to regulate genetic expression based on their respective population density and has emerged as an attractive target for therapeutic intervention. By interfering with bacterial quorum sensing, for instance, enzymatic degradation of signalling molecules (quorum quenching) or the application of quorum sensing inhibitory compounds, it may be possible to modulate the microbial composition of communities of interest without incurring negative effects associated with traditional antimicrobial approaches. In this review, we summarise and critically discuss the literature relating to quorum sensing from the perspective of the interactions between the food and human gut microbiome, providing a general overview of the current understanding of the prevalence and influence of quorum sensing in this context, and assessing the potential for therapeutic targeting of quorum sensing mechanisms.

LuxS-mediated quorum sensing system in Lactobacillus plantarum NMD-17 from koumiss: induction of plantaricin MX in co-cultivation with certain lactic acid bacteria

A bacteriocin termed plantaricin MX with a broad antimicrobial spectrum was produced by Lactobacillus plantarum NMD-17, which was isolated from Inner Mongolia traditional koumiss of china. Among 300 strains of lactic acid bacteria (LAB) belonging to the genera Lactococcus, Lactobacillus, Streptococcus, Leuconostoc, and Enterococcus, five strains including Lactobacillus reuteri NMD-86, Lactobacillus helveticus NMD-137, Lactococcus lactis NMD-152, Enterococcus faecalis NMD-178, and Enterococcus faecium NMD-219 were revealed to significantly induce the bacteriocin synthesis and greatly increase the cell numbers of Lactobacillus plantarum NMD-17 and activity of AI-2 signaling molecule. Bacteriocin synthesis was not increased by cell-free supernatants and autoclaved cultures of inducing strains, demonstrating that intact cells of inducing strains were essential to the induction of bacteriocin synthesis. The existence of bacteriocin structural plnEF genes and the plnD and luxS genes involved in quorum sensing was confirmed by PCR, and the presence of plnB gene encoding histidine protein kinase was determined by single oligonucleotide nested PCR (Son-PCR). Quantitative real-time PCR demonstrated that plnB, plnD, luxS, plnE, and plnF genes of L. plantarum NMD-17 were upregulated significantly (P < 0.01) in co-cultivation with L. reuteri NMD-86. The results showed that the bacteriocin synthesis of L. plantarum NMD-17 in co-cultivation might have a close relationship with LuxS-mediated quorum sensing system.

Probiotics: an Antibiotic Replacement Strategy for Healthy Broilers and Productive Rearing

Pathogens develop resistance to antibiotics at a rate much faster than the discovery of new antimicrobial compounds. Reports of multidrug-resistant bacteria isolated from broilers, and the possibility that these strains may spread diseases amongst humans, prompted many European countries to ban the inclusion of antibiotics in feed. Probiotics added to broiler feed controlled a number of bacterial infections. A combination of Enterococcus faecium, Pediococcus acidilactici, Bacillus animalis, Lactobacillus salivarius and Lactobacillus reuteri decreased the colonisation of Campylobacter jejuni and Salmonella Enteritidis in the gastro-intestinal tract (GIT) of broilers, whereas Bacillus subtilis improved feed conversion, intestinal morphology, stimulated the immune system and inhibited the colonisation of Campylobacter jejuni, Escherichia coli and Salmonella Minnesota. Lactobacillus salivarius and Pediococcus parvulus improved weight gain, bone characteristics, intestinal morphology and immune response, and decreased the colonisation of S. Enteritidis. Lactobacillus crispatus, L. salivarius, Lactobacillus gallinarum, Lactobacillus johnsonii, Enterococcus faecalis and Bacillus amyloliquefaciens decreased the Salmonella count and led to an increase in lysozyme and T lymphocytes. Probiotics may also improve feed digestion through production of phytases, lipases, amylases and proteases or stimulate the GIT to secrete digestive enzymes. Some strains increase the nutritional value of feed by production of vitamins, exopolysaccharides and antioxidants. Bacteriocins, if produced, regulate pathogen numbers in the GIT and keep pro-inflammatory and anti-inflammatory reactions in balance.

Pediococcus acidilactici Strains Improve Constipation Symptoms and Regulate Intestinal Flora in Mice

Constipation is a prevalent gastrointestinal disorder that seriously reduces the quality of life. Clinical studies have shown that a great change or severe imbalance occurs in the intestinal microbiota of people with constipation. This study explored whether bacteriocin-producing and non-bacteriocin-producing Pediococcus acidilactici strains resulted in differences in the alleviation of constipation and changes in the fecal flora in BALB/c mice. The constipation-related indicators, gastrointestinal regulatory peptides and gut microbiota were identified to evaluate their alleviating effects and underlying mechanisms. The time to the first black-stool defecation and the gastrointestinal transit rate in constipated mice were found to be somewhat improved by four P. acidilactici strains (P > 0.05). Moreover, there were significant differences in the level of most gastrointestinal regulatory peptides in the serum, as well as in the composition and abundance of intestinal microbiota in different groups (P < 0.05). At the phylum level, the relative abundance of Firmicutes was significantly increased, but those of Bacteroidetes and Proteobacteria were significantly reduced after the administration of four P. acidilactici strains for 14 d (P < 0.05). The levels of Bacteroides and genera from Enterobacteriaceae were significantly decreased, whereas Bifidobacterium and Lactobacillus were upregulated when bacteriocin-producing P. acidilactici CCFM18 and CCFM28 strains were provided in the diet (P < 0.05). The results indicated that although constipation-related symptoms were alleviated to only a limited degree, the administration of four P. acidilactici strains effectively regulated the gut flora and provided a potential health benefit to the host, especially the bacteriocin-producing P. acidilactici strains.

Biofilm-Forming Ability of Microbacterium lacticum and Staphylococcus capitis Considering Physicochemical and Topographical Surface Properties

Biofilm characteristics of Microbacterium lacticum D84 (M. lacticum) and Staphylococcus capitis subsp. capitis (S. capitis) on polytetrafluoroethylene and AISI-304 stainless steel at early- (24, 48 h) and late-stage (144, 192 h) biofilm formation were investigated. M. lacticum biofilm structure was more developed compared to S. capitis, representing vastly mature biofilms with a strongly developed amorphous matrix, possibly extracellular polymeric substances (EPSs), at late-stage biofilm formation. S. capitis showed faster growth behavior but still resulted in a relatively flat biofilm structure. Strong correlations were found between several roughness parameters and S. capitis surface coverage (r ≥ 0.98), and between total surface free energy (γs) and S. capitis surface coverage (r = 0.89), while M. lacticum remained mostly unaffected. The pronounced ubiquitous biofilm characteristics make M. lacticum D84 a suitable model for biofilm research. Studying biofilm formation of these bacteria may help one understand bacterial adhesion on interfaces and hence reduce biofilm formation in the food industry.

It's Not Easy Being Green: A Narrative Review on the Microbiology, Virulence and Therapeutic Prospects of Multidrug-Resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is the most frequent cause of infection among non-fermenting Gram-negative bacteria, predominantly affecting immunocompromised patients, but its pathogenic role should not be disregarded in immunocompetent patients. These pathogens present a concerning therapeutic challenge to clinicians, both in community and in hospital settings, due to their increasing prevalence of resistance, and this may lead to prolonged therapy, sequelae, and excess mortality in the affected patient population. The resistance mechanisms of P. aeruginosa may be classified into intrinsic and acquired resistance mechanisms. These mechanisms lead to occurrence of resistant strains against important antibiotics-relevant in the treatment of P. aeruginosa infections-such as β-lactams, quinolones, aminoglycosides, and colistin. The occurrence of a specific resistotype of P. aeruginosa, namely the emergence of carbapenem-resistant but cephalosporin-susceptible (Car-R/Ceph-S) strains, has received substantial attention from clinical microbiologists and infection control specialists; nevertheless, the available literature on this topic is still scarce. The aim of this present review paper is to provide a concise summary on the adaptability, virulence, and antibiotic resistance of P. aeruginosa to a readership of basic scientists and clinicians.

Interplay between gut microbiota and antimicrobial peptides

The gut microbiota is comprised of a diverse array of microorganisms that interact with immune system and exert crucial roles for the health. Changes in the gut microbiota composition and functionality are associated with multiple diseases. As such, mobilizing a rapid and appropriate antimicrobial response depending on the nature of each stimulus is crucial for maintaining the balance between homeostasis and inflammation in the gut. Major players in this scenario are antimicrobial peptides (AMP), which belong to an ancient defense system found in all organisms and participate in a preservative co-evolution with a complex microbiome. Particularly increasing interactions between AMP and microbiota have been found in the gut. Here, we focus on the mechanisms by which AMP help to maintain a balanced microbiota and advancing our understanding of the circumstances of such balanced interactions between gut microbiota and host AMP. This review aims to provide a comprehensive overview on the interplay of diverse antimicrobial responses with enteric pathogens and the gut microbiota, which should have therapeutic implications for different intestinal disorders.

Nisin Production by Enterococcus hirae DF105Mi Isolated from Brazilian Goat Milk

The purpose of this study was to select the promising biopreservation bacteriocin producer strain from goat milk and characterize the expressed bacteriocin, related to its physiological and biochemical properties and specificity of operon encoding production and expression of antimicrobial peptide. Brazilian goat milk was used as the source for the selection of bacteriocin-producing lactic acid bacteria. One strain (DF105Mi) stood out for its strong activity against several Listeria monocytogenes strains. Selected strain was identified based on the biochemical and physiological characteristics and 16s rRNA analysis. The bacteriocin production and inhibitory spectrum of strain DF105Mi were studied, together with the evaluation of the effect of temperature, pH, and chemicals on bacteriocin stability and production, activity, and adsorption to target cells as well as to the cell surface of bacteriocin producers. Physiological and bio-molecular analyses based on targeting of different genes, parts of nisin operon were performed in order to investigate the hypothesis that the studied strain can produce and express nisin. Based on biochemical, physiological, and 16s rRNA analysis, the strain DF105Mi was classified as Enterococcus hirae. The selected strain produces a bacteriocin which is stable in a wide range of pH (2.0-12.0), temperature (up to 120 °C), presence of selected chemicals and presents adsorption affinity to different test organisms, process influenced by environmental conditions. Higher bacteriocin production by Ent. hirae DF105Mi was recorded during stationary growth phase, but only when the strain was cultured at 37 °C. The strain's genetic analysis indicated presence of the genes coding for the production of the bacteriocin nisin. This result was confirmed by cross-checking the sensitivity of the produced strain to commercial nisin A. The strong anti-Listeria activity, bacteriocin adsorption, and stability of produced bacteriocin indicate that Ent. hirae DF105Mi presents a differentiated potential application for biopreservation of fermented dairy products.

SprI/SprR Quorum Sensing System of Serratia proteamaculans 94

In this study, we investigated the quorum sensing (QS) regulatory system of the psychrotrophic strain Serratia proteamaculans 94 isolated from spoiled refrigerated meat. The strain produced several N-acyl-L-homoserine-lactone (AHL) QS signal molecules, with N-(3-oxo-hexanoyl)-L-homoserine lactone and N-(3-hydroxy-hexanoyl)-L-homoserine lactone as two main types. The sprI and sprR genes encoding an AHL synthase and a receptor regulatory protein, respectively, were cloned and sequenced. Analysis of their nucleotide sequence showed that these genes were transcribed convergently and that their reading frames partly overlapped by 23 bp in the terminal regions. The genes were highly similar to the luxI/luxR-type QS genes of other Gram-negative bacteria. An spr-box (analog of the lux-box) was identified upstream of the sprR gene and found to be overlapped with the sequence of -10 sequence site in the promoter region of this gene. Inactivation of the sprI gene led to the absence of AHL synthesis, chitinolytic activity, and swimming motility; decrease of extracellular proteolytic activity; affected the cellular fatty acid composition; and reduced suppression of the fungal plant pathogen mycelium growth by volatile compounds emitted by strain S. proteamaculans 94. The data obtained demonstrated the important role of the QS system in the regulation of cellular processes in S. proteamaculans 94.

Lactic Acid Bacteria in Finfish-An Update

A complex and dynamic community of microorganisms, play important roles within the fish gastrointestinal (GI) tract. Of the bacteria colonizing the GI tract, are lactic acid bacteria (LAB) generally considered as favorable microorganism due to their abilities to stimulating host GI development, digestive function, mucosal tolerance, stimulating immune response, and improved disease resistance. In early finfish studies, were culture-dependent methods used to enumerate bacterial population levels within the GI tract. However, due to limitations by using culture methods, culture-independent techniques have been used during the last decade. These investigations have revealed the presence of Lactobacillus, Lactococcus, Leuconostoc, Enterococcus, Streptococcus, Carnobacterium, Weissella, and Pediococcus as indigenous species. Numerous strains of LAB isolated from finfish are able to produce antibacterial substances toward different potential fish pathogenic bacteria as well as human pathogens. LAB are revealed be the most promising bacterial genera as probiotic in aquaculture. During the decade numerous investigations are performed on evaluation of probiotic properties of different genus and species of LAB. Except limited contradictory reports, most of administered strains displayed beneficial effects on both, growth-and reproductive performance, immune responses and disease resistance of finfish. This eventually led to industrial scale up and introduction LAB-based commercial probiotics. Pathogenic LAB belonging to the genera Streptococcus, Enterococcus, Lactobacillus, Carnobacterium, and Lactococcus have been detected from ascites, kidney, liver, heart, and spleen of several finfish species. These pathogenic bacteria will be addressed in present review which includes their impacts on finfish aquaculture, possible routes for treatment. Finfish share many common structures and functions of the immune system with warm-blooded animals, although apparent differences exist. This similarity in the immune system may result in many shared LAB effects between finfish and land animals. LAB-fed fish show an increase in innate immune activities leading to disease resistances: neutrophil activity, lysozyme secretion, phagocytosis, and production of pro-inflammatory cytokines (IL-1β, IL-6, IL-8, and TNF-α). However, some LAB strains preferentially induces IL-10 instead, a potent anti-inflammatory cytokine. These results indicate that LAB may vary in their immunological effects depending on the species and hosts. So far, the immunological studies using LAB have been focused on their effects on innate immunity. However, these studies need to be further extended by investigating their involvement in the modulation of adaptive immunity. The present review paper focuses on recent findings in the field of isolation and detection of LAB, their administration as probiotic in aquaculture and their interaction with fish immune responses. Furthermore, the mode of action of probiotics on finfish are discussed.

Biochemical Features of Beneficial Microbes: Foundations for Therapeutic Microbiology

Commensal and beneficial microbes secrete myriad products which target the mammalian host and other microbes. These secreted substances aid in bacterial niche development, and select compounds beneficially modulate the host and promote health. Microbes produce unique compounds which can serve as signaling factors to the host, such as biogenic amine neuromodulators, or quorum-sensing molecules to facilitate inter-bacterial communication. Bacterial metabolites can also participate in functional enhancement of host metabolic capabilities, immunoregulation, and improvement of intestinal barrier function. Secreted products such as lactic acid, hydrogen peroxide, bacteriocins, and bacteriocin-like substances can also target the microbiome. Microbes differ greatly in their metabolic potential and subsequent host effects. As a result, knowledge about microbial metabolites will facilitate selection of next-generation probiotics and therapeutic compounds derived from the mammalian microbiome. In this article we describe prominent examples of microbial metabolites and their effects on microbial communities and the mammalian host.

Assessment of hemolytic activity, enzyme production and bacteriocin characterization of Bacillus subtilis LR1 isolated from the gastrointestinal tract of fish

In the present investigation, probiotic potential (antagonistic activity, enzyme production, hemolytic activity, biosafety, antibiotic sensitivity and bile tolerance level) of Bacillus subtilis LR1 was evaluated. Bacteriocin produced by the bacterial strain B. subtilis LR1 isolated from the gastrointestinal tract of Labeo rohita was purified and characterized. The molecular weight of the purified bacteriocin was ~50 kDa in 12 % Native PAGE and showed inhibitory activity against four fish pathogens such as Bacillus mycoides, Aeromonas salmonicida, Pseudomonas fluorescens and Aeromonas hydrophila. The purified bacteriocin was maximally active at temperature 40 °C and pH 7.0, while none of the tested surfactants affect the bacteriocin activity. Extracellular enzyme activity of the selected bacterial strain was also evaluated. Amylase activity was estimated to be highest (38.23 ± 1.15 µg of maltose liberated mg^-1 protein ml^-1 of culture filtrate) followed by cellulase and protease activity. The selected bacterium was sensitive to most of the antibiotics used in this experiment, can tolerate 0.25 % bile salt and non-hemolytic in nature. Finally, the efficiency of the proposed probiotic candidate was evaluated in in vivo condition. It was detected that the bacterial strain can effectively reduce bacterial pathogenicity in Indian major carps.

Investigation of genes involved in nisin production in Enterococcus spp. strains isolated from raw goat milk

Different strains of Lactococcus lactis are capable of producing the bacteriocin nisin. However, genetic transfer mechanisms allow the natural occurrence of genes involved in nisin production in members of other bacterial genera, such as Enterococcus spp. In a previous study, nisA was identified in eight enterococci capable of producing antimicrobial substances. The aim of this study was to verify the presence of genes involved in nisin production in Enterococcus spp. strains, as well as nisin expression. The nisA genes from eight Enterococcus spp. strains were sequenced and the translated amino acid sequences were compared to nisin amino-acid sequences previously described in databases. Although containing nisin structural and maturation related genes, the enterococci strains tested in the present study did not present the immunity related genes (nisFEG and nisI). The translated sequences of nisA showed some point mutations, identical to those presented by Lactococcus strains isolated from goat milk. All enterococci were inhibited by nisin, indicating the absence of immunity and thus that nisin cannot be expressed. This study demonstrated for the first time the natural occurrence of nisin structural genes in Enterococcus strains and highlights the importance of providing evidence of a link between the presence of bacteriocin genes and their expression.

Autoinducer-2 properties of kimchi are associated with lactic acid bacteria involved in its fermentation

Bacteria use the cell density-dependent quorum signalling system to regulate particular gene expressions. In food microbiology, signalling is well known for its relation to (foodborne) pathogenicity, food spoilage, and biofilm formation. Quorum quenching and inhibition are thus being considered as a feasible approach in food preservation and safety. In the case of the luxS-mediated universal quorum sensing using autoinducer-2 (AI-2), however, it could be a different issue. Several studies have reported a luxS AI-2 synthase homologue in numerous bacteria, comprising both pathogens and beneficial strains. A recent study has shown the AI-2 signal to restore the balance of the major phyla of the gut microbiota in antibiotic-induced dysbiosis. We measured the AI-2 activity of the lactic fermented food, kimchi, and found different AI-2 signalling intensities. In order to trace the origin of the signal production, we obtained 229 lactic acid bacterial isolates from the kimchi samples, and detected the AI-2 properties of each isolate using a modified AI-2 bioluminescence assay. Our results showed isolates of dominant species of the genera Lactobacillus, Weissella and Leuconostoc which either produced or inhibited the AI-2 signal. No isolate of the dominant species Lactobacillus sakei (75 isolates) and Lactobacillus curvatus (28 isolates) showed AI-2 producing activity, while AI-2 inhibition could not be detected for any of the 31 Lactobacillus plantarum isolates. These results suggest the AI-2 activity of kimchi to result from the interaction of the associated microbial food cultures (MFCs) during fermentation. Thus far, only sparse information is available on AI-2 signalling interaction in fermented food, however, we suggest that fermented food may be a supplier of AI-2 signalling molecules via typical MFCs.

AguR, a Transmembrane Transcription Activator of the Putrescine Biosynthesis Operon in Lactococcus lactis, Acts in Response to the Agmatine Concentration

Dairy industry fermentative processes mostly use Lactococcus lactis as a starter. However, some dairy L. lactis strains produce putrescine, a biogenic amine that raises food safety and spoilage concerns, via the agmatine deiminase (AGDI) pathway. The enzymatic activities responsible for putrescine biosynthesis in this bacterium are encoded by the AGDI gene cluster. The role of the catabolic genes aguB, aguD, aguA, and aguC has been studied, but knowledge regarding the role of aguR (the first gene in the cluster) remains limited. In the present work, aguR was found to be a very low level constitutively expressed gene that is essential for putrescine biosynthesis and is transcribed independently of the polycistronic mRNA encoding the catabolic genes (aguBDAC). In response to agmatine, AguR acts as a transcriptional activator of the aguB promoter (PaguB), which drives the transcription of the aguBDAC operon. Inverted sequences required for PaguB activity were identified by deletion analysis. Further work indicated that AguR is a transmembrane protein which might function as a one-component signal transduction system that senses the agmatine concentration of the medium and, accordingly, regulates the transcription of the aguBDAC operon through a C-terminal cytoplasmic DNA-binding domain typically found in LuxR-like proteins.

Synthesis, Antimicrobial, Antiquorum-Sensing, and Cytotoxic Activities of New Series of Isoindoline-1,3-dione, Pyrazolo[5,1-a]isoindole, and Pyridine Derivatives

New series of isoindoline-1,3-diones 2-9, pyrazolo[5,1-a]isoindoles 10-14, and pyridines 16-18 were synthesized. Twenty of the synthesized compounds were screened for their antibacterial activity against S. aureus, B. cereus, and E. coli. Compound 5 was proved to be the most active member in this study, showing the highest antibacterial activity against the three selected microorganisms. The antifungal activity of these compounds was also tested against C. albicans and A. flavus 3375. Compounds 4, 5, 8, and 17a exhibited the best antifungal activity against A. flavus 3375. The same compounds were examined for their antiquorum-sensing activity against Ch. violacium ATCC 12472, whereas compound 5 displayed strong antiquorum-sensing activity. The in vitro cytotoxicity testing of compounds 4-9 and 17a against human normal lung fibroblast (W138) cell line revealed that compounds 4, 5, and 8 are the least cytotoxic analogs in this study. In vivo acute toxicity testing of compounds 4, 5, and 8 was performed. The DNA-binding affinity of compounds 4-9 and 17a was also tested and the obtained results showed that all tested compounds have moderate DNA-binding affinity.

Gene cluster responsible for secretion of and immunity to multiple bacteriocins, the NKR-5-3 enterocins

Enterococcus faecium NKR-5-3, isolated from Thai fermented fish, is characterized by the unique ability to produce five bacteriocins, namely, enterocins NKR-5-3A, -B, -C, -D, and -Z (Ent53A, Ent53B, Ent53C, Ent53D, and Ent53Z). Genetic analysis with a genome library revealed that the bacteriocin structural genes (enkA [ent53A], enkC [ent53C], enkD [ent53D], and enkZ [ent53Z]) that encode these peptides (except for Ent53B) are located in close proximity to each other. This NKR-5-3ACDZ (Ent53ACDZ) enterocin gene cluster (approximately 13 kb long) includes certain bacteriocin biosynthetic genes such as an ABC transporter gene (enkT), two immunity genes (enkIaz and enkIc), a response regulator (enkR), and a histidine protein kinase (enkK). Heterologous-expression studies of enkT and ΔenkT mutant strains showed that enkT is responsible for the secretion of Ent53A, Ent53C, Ent53D, and Ent53Z, suggesting that EnkT is a wide-range ABC transporter that contributes to the effective production of these bacteriocins. In addition, EnkIaz and EnkIc were found to confer self-immunity to the respective bacteriocins. Furthermore, bacteriocin induction assays performed with the ΔenkRK mutant strain showed that EnkR and EnkK are regulatory proteins responsible for bacteriocin production and that, together with Ent53D, they constitute a three-component regulatory system. Thus, the Ent53ACDZ gene cluster is essential for the biosynthesis and regulation of NKR-5-3 enterocins, and this is, to our knowledge, the first report that demonstrates the secretion of multiple bacteriocins by an ABC transporter.

Characterization of the antifungal activity of Lactobacillus harbinensis K.V9.3.1Np and Lactobacillus rhamnosus K.C8.3.1I in yogurt

Few antifungal protective cultures adapted to fermented dairy products are commercially available because of the numerous constraints linked to their market implementation. Consumer's demand for naturally preserved food products is growing and the utilization of lactic acid bacteria is a promising way to achieve this goal. In this study, using a 2(5-1) factorial fractional design, we first evaluated the effects of fermentation time, of initial sucrose concentration and of the initial contamination amount of a spoilage yeast, on antifungal activities of single and mixed cultures of Lactobacillus rhamnosus K.C8.3.1I and Lactobacillus harbinensis K.V9.3.1Np in yogurt. L. harbinensis K.V9.3.1Np, the most relevant strain with regard to antifungal activity was then studied to determine its minimal inhibitory inoculation rate, its antifungal stability during storage and its impact on yogurt organoleptic properties. We showed that L. harbinensis K.V9.3.1Np maintained a stable antifungal activity over time, which was not affected by initial sucrose, nor by a reduction of the fermentation time. This inhibitory activity was an all-or-nothing phenomenon. Once L. harbinensis K.V9.3.1Np reached a population of ∼ 2.5 × 10(6) cfu/g of yogurt at the time of contamination, total inhibition of the yeast was achieved. We also showed that an inoculation rate of 5 × 10(6) cfu/ml in milk had no detrimental effect on yogurt organoleptic properties. In conclusion, L. harbinensis K.V9.3.1Np is a promising antifungal bioprotective strain for yogurt preservation.

Purification and characterization of bacteriocin produced by oral Lactobacillus paracasei SD1

The present study aimed to purify and characterize the antimicrobial protein from Lactobacillus paracasei SD1, which is a strain from the human oral cavity. Antimicrobial activity was obtained from purifying the culture supernatant of L. paracasei SD1. Purification of the active compound was achieved with ammonium sulfate precipitation followed by chloroform and gel filtration chromatography. As revealed by SDS-PAGE, the active fraction was homogeneous, showing a protein with an approximate molecular weight of 25,000 Da. It was confirmed as having a molecular mass of 24,028.2 Da by mass spectrometry. The antimicrobial compound, named "paracasin SD1", exhibited a broad spectrum against oral pathogens. Paracasin SD1 was stable in a pH range between 3.0 and 8.0 at 100 °C for 5 min, and showed resistance to α-amylase, catalase, lysozyme and whole saliva. However, its activity was lost after proteinase K and trypsin treatment. The results obtained suggest the possibility of using paracasin SD1 for application in prevention/treatment of oral diseases.

Effects of the peptide pheromone plantaricin A and cocultivation with Lactobacillus sanfranciscensis DPPMA174 on the exoproteome and the adhesion capacity of Lactobacillus plantarum DC400

This study aimed at investigating the extracellular and cell wall-associated proteins (exoproteome) of Lactobacillus plantarum DC400 when cultivated on modified chemically defined medium (CDM) supplemented with the chemically synthesized pheromone plantaricin A (PlnA) or cocultured with L. plantarum DPPMA20 or Lactobacillus sanfranciscensis DPPMA174. Compared to monoculture, two-dimensional gel electrophoresis (2-DE) analysis showed that the exoproteome of L. plantarum DC400 was affected by PlnA and cocultivation with strains DPPMA20 and, especially, DPPMA174. The highest similarity of the 2-DE maps was found between DC400 cells cultivated in monoculture and in coculture with strain DPPMA20. Almost all extracellular proteins (22 spots) and cell wall-associated proteins (40 spots) which showed decreased or increased levels of synthesis during growth in CDM supplemented with PlnA and/or in coculture with strain DPPMA20 or DPPMA174 were identified. On the basis of the sequences in the Kyoto Encyclopedia of Genes and Genomes database, changes to the exoproteome concerned proteins involved in quorum sensing (QS), the transport system, stress response, carbohydrate metabolism and glycolysis, oxidation/reduction processes, the proteolytic system, amino acid metabolism, cell wall and catabolic processes, and cell shape, growth, and division. Cultivation with PlnA and cocultivation with strains DPPMA20 and, especially, DPMMA174 markedly increased the capacity of L. plantarum DC400 to form biofilms, to adhere to human Caco-2 cells, and to prevent the adhesion of potential intestinal pathogens. These phenotypic traits were in part related to oversynthesized moonlighting proteins (e.g., DnaK and GroEL, pyruvate kinase, enolase, and glyceraldehyde-3-phosphate dehydrogenase) in response to QS mechanisms and interaction with L. plantarum DPPMA20 and, especially, L. sanfranciscensis DPPMA174.

Mathematical modeling of growth of non-O157 Shiga toxin-producing Escherichia coli in raw ground beef

The objective of this study was to investigate the growth of Shiga toxin-producing Escherichia coli (STEC, including serogroups O45, O103, O111, O121, and O145) in raw ground beef and to develop mathematical models to describe the bacterial growth under different temperature conditions. Three primary growth models were evaluated, including the Baranyi model, the Huang 2008 model, and a new growth model that is based on the communication of messenger signals during bacterial growth. A 5 strain cocktail of freshly prepared STEC was inoculated to raw ground beef samples and incubated at temperatures ranging from 10 to 35 °C at 5 °C increments. Minimum relative growth (<1 log₁₀ cfu/g) was observed at 10 °C, whereas at other temperatures, all 3 phases of growth were observed. Analytical results showed that all 3 models were equally suitable for describing the bacterial growth under constant temperatures. The maximum cell density of STEC in raw ground beef increased exponentially with temperature, but reached a maximum of 8.53 log₁₀ cfu/g of ground beef. The specific growth rates estimated by the 3 primary models were practically identical and can be evaluated by either the Ratkowsky square-root model or a Bělehrádek-type model. The temperature dependence of lag phase development for all 3 primary models was also developed. The results of this study can be used to estimate the growth of STEC in raw ground beef at temperatures between 10 and 35 °C.

PRACTICAL APPLICATION

Incidents of foodborne infections caused by non-O157 Shiga toxin-producing Escherichia coli (STEC) have increased in recent years. This study reports the growth kinetics and mathematical modeling of STEC in ground beef. The mathematical models can be used in risk assessment of STEC in ground beef.

Quorum quenching Bacillus sonorensis isolated from soya sauce fermentation brine

An N-acylhomoserine lactone (AHL)-degrading bacterial strain, L62, was isolated from a sample of fermentation brine of Chinese soya sauce by using rich medium agar supplemented with soya sauce (10% v/v). L62, a rod-shaped Gram positive bacterium with amylolytic activity, was phylogentically related to Bacillus sonorensis by 16S ribosomal DNA and rpoB sequence analyses. B. sonorensis L62 efficiently degraded N-3-oxohexanoyl homoserine lactone and N-octanoylhomoserine lactone. However, the aiiA homologue, encoding an autoinducer inactivation enzyme catalyzing the degradation of AHLs, was not detected in L62, suggesting the presence of a different AHL-degrading gene in L62. To the best of our knowledge, this is the first report of AHL-degrading B. sonorensis from soya sauce liquid state fermentation.

Sugar inhibits the production of the toxins that trigger clostridial gas gangrene

Histotoxic strains of Clostridium perfringens cause human gas gangrene, a devastating infection during which potent tissue-degrading toxins are produced and secreted. Although this pathogen only grows in anaerobic-nutrient-rich habitats such as deep wounds, very little is known regarding how nutritional signals influence gas gangrene-related toxin production. We hypothesize that sugars, which have been used throughout history to prevent wound infection, may represent a nutritional signal against gas gangrene development. Here we demonstrate, for the first time, that sugars (sucrose, glucose) inhibited the production of the main protein toxins, PLC (alpha-toxin) and PFO (theta-toxin), responsible for the onset and progression of gas gangrene. Transcription analysis experiments using plc-gusA and pfoA-gusA reporter fusions as well as RT-PCR analysis of mRNA transcripts confirmed that sugar represses plc and pfoA expression. In contrast an isogenic C. perfringens strain that is defective in CcpA, the master transcription factor involved in carbon catabolite response, was completely resistant to the sugar-mediated inhibition of PLC and PFO toxin production. Furthermore, the production of PLC and PFO toxins in the ccpA mutant strain was several-fold higher than the toxin production found in the wild type strain. Therefore, CcpA is the primary or unique regulatory protein responsible for the carbon catabolite (sugar) repression of toxin production of this pathogen. The present results are analyzed in the context of the role of CcpA for the development and aggressiveness of clostridial gas gangrene and the well-known, although poorly understood, anti-infective and wound healing effects of sugars and related substances.

Bacteriocin production: a probiotic trait?

Bacteriocins are an abundant and diverse group of ribosomally synthesized antimicrobial peptides produced by bacteria and archaea. Traditionally, bacteriocin production has been considered an important trait in the selection of probiotic strains, but until recently, few studies have definitively demonstrated the impact of bacteriocin production on the ability of a strain to compete within complex microbial communities and/or positively influence the health of the host. Although research in this area is still in its infancy, there is intriguing evidence to suggest that bacteriocins may function in a number of ways within the gastrointestinal tract. Bacteriocins may facilitate the introduction of a producer into an established niche, directly inhibit the invasion of competing strains or pathogens, or modulate the composition of the microbiota and influence the host immune system. Here we review the role of bacteriocin production in complex microbial communities and their potential to enhance human health.

Review: The use of direct fed microbials to mitigate pathogens and enhance production in cattle

McAllister, T. A., Beauchemin, K. A., Alazzeh, A. Y., Baah, J., Teather, R. M. and Stanford, K. 2011. Review: The use of direct fed microbials to mitigate pathogens and enhance production in cattle. Can. J. Anim. Sci. 91: 193–211. Direct-fed microbials (DFM) have been employed in ruminant production for over 30 yr. Originally, DFM were used primarily in young ruminants to accelerate establishment of the intestinal microflora involved in feed digestion and to promote gut health. Further advancements led to more sophisticated mixtures of DFM that are targeted at improving fiber digestion and preventing ruminal acidosis in mature cattle. Through these outcomes on fiber digestion/rumen health, second-generation DFM have also resulted in improvements in milk yield, growth and feed efficiency of cattle, but results have been inconsistent. More recently, there has been an emphasis on the development of DFM that exhibit activity in cattle against potentially zoonotic pathogens such as Escherichia coli O157:H7, Salmonella spp. and Staphylococcus aureus. Regulatory requirements have limited the microbial species within DFM products to organisms that are generally recognized as safe, such as lactic acid-producing bacteria (e.g., Lactobacillus and Enterococcus spp.), fungi (e.g., Aspergillus oryzae), or yeast (e.g., Saccharomyces cerevisiae). Direct-fed microbials of rumen origin, involving lactate-utilizing species (e.g., Megasphaera elsdenii, Selenomonas ruminantium, Propionibacterium spp.) and plant cell wall-degrading isolates of Butyrivibrio fibrisolvens have also been explored, but have not been commercially used. Development of DFM that are efficacious over a wide range of ruminant production systems remains challenging because[0] comprehensive knowledge of microbial ecology is lacking. Few studies have employed molecular techniques to study in detail the interaction of DFM with native microbial communities or the ruminant host. Advancements in the metagenomics of microbial communities and the genomics of microbial–host interactions may enable DFM to be formulated to improve production and promote health, responses that are presently often achieved through the use of antimicrobials in cattle.

Autoinducer-2-like activity in lactic acid bacteria isolated from minced beef packaged under modified atmospheres

Fifteen fingerprints (assigned to Leuconostoc spp., Leuconostoc mesenteroides, Weissella viridescens, Leuconostoc citreum, and Lactobacillus sakei) of 89 lactic acid bacteria (LAB) isolated from minced beef stored under modified atmospheres at various temperatures were screened for their ability to exhibit autoinducer-2 (AI-2)-like activity under certain growth conditions. Cellfree meat extracts (CFME) were collected at the same time as the LAB isolates and tested for the presence of AI-2-like molecules. All bioassays were conducted using the Vibrio harveyi BAA-1117 (sensor 1(-), sensor 2(+)) biosensor strain. The possible inhibitory effect of meat extracts on the activity of the biosensor strain was also evaluated. AI-2-like activity was observed for Leuconostoc spp. isolates, but none of the L. sakei strains produced detectable AI-2-like activity. The AI-2-like activity was evident mainly associated with the Leuconostoc sp. B 233 strain, which was the dominant isolate recovered from storage at 10 and 15°C and at the initial and middle stages of storage at chill temperatures (0 and 5°C). The tested CFME samples displayed low AI-2-like activity and inhibited AI-2 activity regardless of the indigenous bacterial populations. The LAB isolated during meat spoilage exhibited AI-2-like activity, whereas the LAB strains retrieved depended on storage time and temperature. The production of AI-2-like molecules may affect the dominance of different bacterial strains during storage. The results provide a basis for further research concerning the effect of storage temperature on the expression of genes encoding AI-2 activity and on the diversity of the ephemeral bacterial population.

Functional microorganisms for functional food quality

Functional microorganisms and health benefits represent a binomial with great potential for fermented functional foods. The health benefits of fermented functional foods are expressed either directly through the interactions of ingested live microorganisms with the host (probiotic effect) or indirectly as the result of the ingestion of microbial metabolites synthesized during fermentation (biogenic effect). Since the importance of high viability for probiotic effect, two major options are currently pursued for improving it--to enhance bacterial stress response and to use alternative products for incorporating probiotics (e.g., ice cream, cheeses, cereals, fruit juices, vegetables, and soy beans). Further, it seems that quorum sensing signal molecules released by probiotics may interact with human epithelial cells from intestine thus modulating several physiological functions. Under optimal processing conditions, functional microorganisms contribute to food functionality through their enzyme portfolio and the release of metabolites. Overproduction of free amino acids and vitamins are two classical examples. Besides, bioactive compounds (e.g., peptides, γ-amino butyric acid, and conjugated linoleic acid) may be released during food processing above the physiological threshold and they may exert various in vivo health benefits. Functional microorganisms are even more used in novel strategies for decreasing phenomenon of food intolerance (e.g., gluten intolerance) and allergy. By a critical approach, this review will aim at showing the potential of functional microorganisms for the quality of functional foods.

Eavesdropping by bacteria: the role of SdiA in Escherichia coli and Salmonella enterica serovar Typhimurium quorum sensing

Many gram-negative bacteria utilize N-acyl-L-homoserine lactones (AHLs) to bind to transcriptional regulators leading to activation or repression of target genes. Escherichia coli and Salmonella enterica do not synthesize AHLs but do contain the AHL receptor, SdiA. Studies reveal that SdiA can bind AHLs produced by other bacterial species and thereby allow E. coli and S. enterica to regulate gene transcription. The Salmonella sdiA gene regulates the rck gene, which mediates Salmonella adhesion and invasion of epithelial cells and the resistance of the organism to complement. In E. coli, there is some evidence that SdiA may regulate genes associated with acid resistance, virulence, motility, biofilm formation, and autoinducer-2 transport and processing. However, there is a lack of information concerning the role of SdiA in regulating growth and survival of E. coli and Salmonella in food environments, and therefore studies in this area are needed.

Competitive interactions in Escherichia coli populations: the role of bacteriocins

Explaining the coexistence of competing species is a major challenge in community ecology. In bacterial systems, competition is often driven by the production of bacteriocins, which are narrow-spectrum proteinaceous toxins that serve to kill closely related species, providing the producer better access to limited resources. Bacteriocin producers have been shown to competitively exclude sensitive, nonproducing strains. However, the dynamics between bacteriocin producers, each lethal to its competitor, are largely unknown. In this study, we used in vitro, in vivo and in silico models to study competitive interactions between bacteriocin producers. Two Escherichia coli strains were generated, each carrying a DNA-degrading bacteriocin (colicins E2 and E7). Using reporter-gene assays, we showed that each DNase bacteriocin is not only lethal to its opponent but, at lower doses, can also induce the expression of its opponent's toxin. In a well-mixed habitat, the E2 producer outcompeted its adversary; however, in structured environments (on plates or in mice colons), the two producers coexisted in a spatially 'frozen' pattern. Coexistence occurred when the producers were initiated with a clumped spatial distribution. This suggests that a 'clump' of each producer can block invasion of the other producer. Agent-based simulation of bacteriocin-mediated competition further showed that mutual exclusion in a structured environment is a relatively robust result. These models imply that colicin-mediated colicin induction enables producers to successfully compete and defend their niche against invaders. This suggests that localized interactions between producers of DNA-degrading toxins can lead to stable coexistence of heterogeneously distributed strains within the bacterial community and to the maintenance of diversity.

Inhibition of the early stage of Salmonella enterica serovar Enteritidis biofilm development on stainless steel by cell-free supernatant of a Hafnia alvei culture

Compounds present in Hafnia alvei cell-free culture supernatant cumulatively negatively influence the early stage of biofilm development by Salmonella enterica serovar Enteritidis on stainless steel while they also reduce the overall metabolic activity of S. Enteritidis planktonic cells. Although acylhomoserine lactones (AHLs) were detected among these compounds, the use of several synthetic AHLs was not able to affect the initial stage of biofilm formation by this pathogen.

Pseudomonas fragi strains isolated from meat do not produce N-acyl homoserine lactones as signal molecules

Quorum sensing (QS) is a signalling mechanism through which bacteria cellular functions are modified to promote access to nutrients and more favorable environmental niches. The frequent occurrence of Pseudomonas spp. in fresh and spoiled meat may involve enhanced gene expression regulated by QS. Several Pseudomonas spp. produce different N-acyl homoserine lactone (AHL) signal molecules. Meat spoilage during aerobic, refrigerated storage is often associated with the presence of Pseudomonas fragi. As with other Pseudomonas species in natural habitats, the dominance and activities of P. fragi in meat may be regulated by QS. In this study, five biosensor strains were used to detect AHL production on three different media by 72 different P. fragi strains isolated from fresh and spoiled meat. Positive and negative AHL-producing strains were used to verify the assays. None of the strains produced detectable quantities of AHLs, even when concentrated cell-free culture supernatants were assayed, nor did exogenous lactones increase biofilm formation in P. fragi strains. However, all isolates produced furanosyl borate diesters (type II autoinducers; AI-2) when tested using the bioluminescent biosensor strain of Vibrio harveyi (BB170). The production of AI-2 was presumed to be of metabolic origin even though Pseudomonas spp. have not been shown to harbor the luxS gene. Thus, the efficient development of P. fragi in fresh meat is not regulated by an AHL-mediated QS system. The mechanism of AI-2 production and its possible role in spoilage dynamics needs further study.

Molecular adaptation of sourdough Lactobacillus plantarum DC400 under co-cultivation with other lactobacilli

This work was aimed at investigating the molecular mechanisms of Quorum Sensing (QS) in Lactobacillus plantarum DC400 when co-cultured with other sourdough lactobacilli. The growth and survival of L. plantarum DC400 was not affected when co-cultivated with Lactobacillus sanfranciscensis DPPMA174 or Lactobacillus rossiae A7. Nevertheless, 2-DE analysis showed that the level of protein expression of L. plantarum DC400 increased under co-culture conditions. Although several proteins were commonly induced in both co-cultures, the highest induction was found in co-culture with L. rossiae A7. Overexpressed proteins, related to QS and stress response mechanisms, were identified: DnaK, GroEL, 30S ribosomal protein S1 and S6, ATP synthase subunit beta, adenosylmethionine synthetase (MetK), phosphopyruvate hydratase, phosphoglycerate kinase, elongation factor Tu, putative manganese-dependent inorganic pyrophosphatase, d-lactate dehydrogenase, triosephosphate isomerase, fructose-bisphosphate aldolase and nucleoside-diphosphate kinase. As shown by real-time PCR, expression of the luxS gene of L. plantarum DC400 was also affected during co-cultivation. According to overexpression of MetK and luxS during co-cultivation, synthesis of AI-2-like substances was also influenced by the type of microbial co-cultures. This study showed that expression of some genes/proteins, also QS-related, in L. plantarum was influenced by co-cultivation of other sourdough lactobacilli.

The ecology, epidemiology and virulence of Enterococcus

Enterococci are Gram-positive, catalase-negative, non-spore-forming, facultative anaerobic bacteria, which usually inhabit the alimentary tract of humans in addition to being isolated from environmental and animal sources. They are able to survive a range of stresses and hostile environments, including those of extreme temperature (5-65 degrees C), pH (4.5-10.0) and high NaCl concentration, enabling them to colonize a wide range of niches. Virulence factors of enterococci include the extracellular protein Esp and aggregation substances (Agg), both of which aid in colonization of the host. The nosocomial pathogenicity of enterococci has emerged in recent years, as well as increasing resistance to glycopeptide antibiotics. Understanding the ecology, epidemiology and virulence of Enterococcus species is important for limiting urinary tract infections, hepatobiliary sepsis, endocarditis, surgical wound infection, bacteraemia and neonatal sepsis, and also stemming the further development of antibiotic resistance.

Virulence gene regulation by the agr system in Clostridium perfringens

A gram-positive anaerobic pathogen, Clostridium perfringens, causes clostridial myonecrosis or gas gangrene in humans by producing numerous extracellular toxins and enzymes that act in concert to degrade host tissue. The agr system is known to be important for the regulation of virulence genes in a quorum-sensing manner in Staphylococcus aureus. A homologue for S. aureus agrBD (agrBD(Sa)) was identified in the C. perfringens strain 13 genome, and the role of C. perfringens agrBD (agrBD(Cp)) was examined. The agrBD(Cp) knockout mutant did not express the theta-toxin gene, and transcription of the alpha- and kappa-toxin genes was also significantly decreased in the mutant strain. The mutant strain showed a recovery of toxin production after the addition of the culture supernatant of the wild-type strain, indicating that the agrBD(Cp) mutant lacks a signal molecule in the culture supernatant. An agr-virR double-knockout mutant was constructed to examine the role of the VirR/VirS two-component regulatory system, a key virulence regulator, in agrBD(Cp)-mediated regulation of toxin production. The double-mutant strain could not be stimulated for toxin production with the wild-type culture supernatant. These results indicate that the agrBD(Cp) system plays an important role in virulence regulation and also suggest that VirR/VirS is required for sensing of the extracellular signal and activation of toxin gene transcription in C. perfringens.

Microbial interactions in cheese: implications for cheese quality and safety

The cheese microbiota, whose community structure evolves through a succession of different microbial groups, plays a central role in cheese-making. The subtleties of cheese character, as well as cheese shelf-life and safety, are largely determined by the composition and evolution of this microbiota. Adjunct and surface-ripening cultures marketed today for smear cheeses are inadequate for adequately mimicking the real diversity encountered in cheese microbiota. The interactions between bacteria and fungi within these communities determine their structure and function. Yeasts play a key role in the establishment of ripening bacteria. The understanding of these interactions offers to enhance cheese flavour formation and to control and/or prevent the growth of pathogens and spoilage microorganisms in cheese.

The dual role of bacteriocins as anti- and probiotics

Bacteria employed in probiotic applications help to maintain or restore a host's natural microbial floral. The ability of probiotic bacteria to successfully outcompete undesired species is often due to, or enhanced by, the production of potent antimicrobial toxins. The most commonly encountered of these are bacteriocins, a large and functionally diverse family of antimicrobials found in all major lineages of Bacteria. Recent studies reveal that these proteinaceous toxins play a critical role in mediating competitive dynamics between bacterial strains and closely related species. The potential use of bacteriocin-producing strains as probiotic and bioprotective agents has recently received increased attention. This review will report on recent efforts involving the use of such strains, with a particular focus on emerging probiotic therapies for humans, livestock, and aquaculture.