Genomic subpopulations within the species Pediococcus acidilactici detected by multilocus typing analysis: relationships between pediocin AcH/PA-1 producing and non-producing strains

Prevalence of macrolide-lincosamide-streptogramin resistant lactic acid bacteria isolated from food samples

Lactic acid bacteria (LAB) being a reservoir of antibiotic resistance genes, tend to disseminate antibiotic resistance that possibly pose a threat to human and animal health. Therefore, the study focuses on the prevalence of macrolide-lincosamide-streptogramin- (MLS) resistance among LAB isolated from various food samples. Diverse phenotypic and genotypic MLS resistance were determined among the LAB species (n = 146) isolated from fermented food products (n = 6) and intestine of food-producing animals (n = 4). Double disc, triple disc diffusion and standard minimum inhibitory concentration (MIC) tests were evaluated for phenotypic MLS resistance. Specific primers for MLS resistance genes were used for the evaluation of genotypic MLS resistance and gene expressions using total RNA of each isolate at different antibiotic concentrations. The isolates identified are Levilactobacillus brevis (n = 1), Enterococcus hirae (n = 1), Limosilactobacillus fermentum (n = 2), Pediococcus acidilactici (n = 3), Enterococcus faecalis (n = 1). The MIC tests along with induction studies displayed cMLSb, L phenotype, M phenotype, KH phenotype, I phenotype resistance among MLS antibiotics. Genotypic evaluation tests revealed the presence of ermB, mefA/E, msrA/B and msrC genes. Also, gene expression studies displayed increased level of gene expression to the twofold increased antibiotic concentrations. In the view of global health concern, this study identified that food samples and food-producing animals represent source of antibiotic resistant LAB that can disseminate resistance through food chain. This suggests the implementation of awareness in the use of antibiotics as growth promoters and judicious use of antibiotics in veterinary sectors in order to prevent the spread of antibiotic resistance.

Beneficial features of pediococcus: from starter cultures and inhibitory activities to probiotic benefits

Pediococci are lactic acid bacteria (LAB) which have been used for centuries in the production of traditional fermented foods. There fermentative abilities were explored by the modern food processing industry in use of pediococci as starter cultures, enabling the production of fermented foods with distinct characteristics. Furthermore, some pediococci strains can produce bacteriocins and other antimicrobial metabolites (AMM), such as pediocins, which are increasingly being explored as bio-preservatives in various food matrices. Due to their versatility and inhibitory spectrum, pediococci bacteriocins and AMM are being extensively researched not only in the food industry, but also in veterinary and human medicine. Some of the pediococci were evaluated as potential probiotics with different beneficial areas of application associated with human and other animals' health. The main taxonomic characteristics of pediococci species are presented here, as well as and their potential roles and applications as starter cultures, as bio-preservatives and as probiotic candidates.

In vitro and in silico approach for characterization of antimicrobial peptides from potential probiotic cultures against Staphylococcus aureus and Escherichia coli

The focus of the present study was to characterize antimicrobial peptide produced by potential probiotic cultures of Enterococcus durans DB-1aa (MCC4243), Lactiplantibacillus plantarum Cu2-PM7 (MCC4246) and Limosilactobacillus fermentum Cu3-PM8 (MCC4233) against Staphylococus aureus MTCC 96 and Escherichia coli MTCC118. The growth kinetic assay revealed 24 h of incubation to be optimum for bacteriocin production. The partially purified compound of all the three selected cultures after ion-exchange chromatography was found to be thermoresistant and stable under a wide range of pH. The compound was sensitive to proteinase-K, but resistant to trypsin, α-amylase and lipase. Comparatively, bacteriocins from L. fermentum Cu3-PM8 and L. plantarum Cu2-PM7 showed higher stability under studied parameter, hence was taken up for further investigation. The apparent molecular weight of bacteriocin from L. fermentum MCC4233 and L. plantarum MCC4246 was found to be 3.5 kDa. Further, plantaricin gene from MCC4246 was characterized in silico. The translated partial amino acid sequence of the plnA gene in MCC4246 displayed 48 amino acids showing 100 % similarity with plantaricin A of Lactobacillus plantarum (WP_0036419). The sequence revealed 7 β sheets, 6 α sheets, 6 predicted coils and 9 predicted turns. The predicted properties of the peptide included an isoelectric point of 10.82 and a hydrophobicity of 48.6 %. The molecular approach of using Geneious Prime software and protein prediction data base for characterization of bacteriocin is novel and predicts "KSSAYSLQMGATAIKQVKKLFKKWGW" to be a peptide responsible for antimicrobial activity. The study provides information about a broad spectrum bacteriocin in native probiotic culture and paves a way towards its application in functional foods as a biopreservative agent.

Multilocus Sequence Typing of Leuconostoc mesenteroides Strains From the Qinghai-Tibet Plateau

Leuconostoc mesenteroides strains were a type of epiphytic bacterium widely used in fermented foods and products in the biochemical and pharmaceutical industries but data on its presence in foods from Qinghai-Tibet Plateau in China was scarce. In this study, molecular analysis based on multilocus sequence typing (MLST) with eight housekeeping genes (pyrG, groeL, rpoB, recA, uvrC, murC, carB, and pheS) was carried out on 45 L. mesenteroides strains isolated from different plants and dairy products from Qinghai-Tibet Plateau in China. The objective of this study was to perform genetic diversity analysis and explore the relationship between strains and isolate samples or separate regions. A total of 25 sequence types (STs) were identified with a diversity of up to 55.6%, which were grouped into one clonal complexes (CCs), 3 doublets and 17 singletons by eBURST. The results of minimum spanning tree and clustering analysis indicated these L. mesenteroides strains from the Qinghai-Tibet Plateau were relatively weakly related to the isolated region. However, there was a close relationship between the genotypes of L. mesenteroides strains and the type of the isolated sample, which was consistent with the results of API 50CH. The MLST scheme presented in this study provides a shareable and comparable sequence database and enhances our knowledge of the population diversity of L. mesenteroides strains which will be further used for the selection of industrial strains.

Identification and in vitro evaluation of probiotic attributes of lactic acid bacteria isolated from fermented food sources

Consumer's vigilance towards health-promoting foods beyond only taste and nutrition has increased the recognition for probiotic products. In the present study, various parameters have been studied to define the probiotic properties of cultures isolated from different fermented products. Around 118 samples were selectively screened for antimicrobial compound (AMC) producing isolates by overlay-plate assay using Micrococcus luteus ATCC9341. Among 134 zone producing isolates, 48 cultures showing Gram-positive, catalase negative, non-spore forming and non-motile rods and cocci were selected. Subsequently, 18 strains were chosen based on non-hemolytic, absence of biogenic amine production, gelatinase and lecithinase negative trait for safer isolates. These were identified by biochemical assays and then subjected to RAPD-PCR. The selected cultures DB-1aa, DB-b2-15b, Cu2-PM7, Cu3-PM8 and IB-pM15 were identified by 16S rDNA sequencing as Enterococcus durans, Enterococcus faecium, Lactobacillus plantarum, and two Lactobacillus fermentum, respectively. Several in vitro experiments were carried out including acid and bile tolerance, survival under simulated gastrointestinal condition, adhesion assay to evaluate the probiotic potential of the isolates. In addition, the isolates were studied for competent properties such as antibacterial, antioxidant activity, and enzyme production for their functional application. The results of the study prove the efficiency of selected isolates as potential probiotic cultures and hence can be recommended for application in any functional food formulations.

In vivo safety assessment of Lactobacillus fermentum strains, evaluation of their cholesterol-lowering ability and intestinal microbial modulation

BACKGROUND

Despite the growing importance of probiotics apparent health benefits, an impediment to the use of new probiotic cultures is their safety. Hence there is a need to strictly examine the biosafety as well as health benefits of probiotics in in vivo model systems.

RESULTS

In this study, two lactic acid bacterial (LAB) cultures Lactobacillus fermentum NCMR 2826 and FIX proven for their in vitro probiotic properties were investigated for their in vivo safety in Wistar rats. An acute toxicity study (14 days) with a high dose of biomass (10¹⁶ colony-forming units (CFU) mL^-1 ) followed by a subchronic test for 13 weeks with oral feeding of the probiotic cultures in three different doses (10⁷ , 10⁸ and 10¹⁰ CFU mL^-1 ) on a daily basis revealed the safety of the L. fermentum cultures. The probiotic feeding had no toxic effects on survival, body weight and food consumption with any of the dosages used throughout the treatment period. No statistically significant changes in relative organ weights and serum biochemical and hematological indices were found between the control and the probiotic fed animals. In addition to the safety attributes, the L. fermentum culture fed rats showed reduced serum cholesterol levels, macrovesicular steatosis and hepatocyte ballooning compared with control animals. Further, quantification of intestinal microbiota using real-time polymerase chain reaction (PCR) analysis from animal feces indicated a significant increase and stability of Lactobacillus and Bifidobacterium counts but a decrease of Escherichia coli numbers.

CONCLUSION

This study of safety and beneficial features highlights the use of the two native L. fermentum isolates as potential probiotic food supplements. © 2019 Society of Chemical Industry.

Heterogeneity of macrolide-lincosamide-streptogramin phenotype & conjugal transfer of erm(B) in Pediococcus pentosaceus

Background & objectives:

Pediococcus pentosaceus has been reported to cause clinical infections while it is being promoted as probiotic in food formulations. Antibiotic resistance (AR) genes in this species are a matter of concern for treating clinical infections. The present study was aimed at understanding the phenotypic resistance of P. pentosaceus to macrolide-lincosamide-streptogramin B (MLS_B) antibiotics and the transfer of AR to pathogens.

Methods:

P. pentosacues isolates (n=15) recovered from fermented foods were screened for phenotypic resistance to MLS_B antibiotics using disc diffusion and microbroth dilution methods. Localization and transferability of the identified resistance genes, erm(B) and msr(C) were evaluated through Southern hybridization and in vitro conjugation methods.

Results:

Four different phenotypes; sensitive (S) (n=5), macrolide (M) (n=7), lincosamide (L) (n=2) and constitutive (cMLS_B) (n=1) were observed among the 15 P. pentosaceus isolates. High-level resistance (>256 μg/ml) to MLS_B was observed with one cMLS_B phenotypic isolate IB6-2A. Intermediate resistance (8-16 μg/ml) to macrolides and lincosamides was observed among M and L phenotype isolates, respectively. Cultures with S phenotype were susceptible to all other antibiotics but showed unusual minimum inhibitory concentration (MIC) values of 8-16 μg/ml for azithromycin. Southern hybridization studies revealed that resistance genes localized on the plasmids could be conjugally transferred to Enterococcus faecalis JH2-2.

Interpretation & conclusions:

The study provides insights into the emerging novel resistance patterns in P. pentosaceus and their ability to disseminate AR. Monitoring their resistance phenotypes before use of MLS antibiotics can help in successful treatment of Pediococcal infections in humans.

Conjugal transfer of erm(B) and multiple tet genes from Lactobacillus spp. to bacterial pathogens in animal gut, in vitro and during food fermentation

Three strains of Lactobacillus comprising Lactobacillus salivarius (CHS-1E and CH7-1E) and Lactobacillus reuteri (CH2-2) previously isolated from chicken meat were analyzed for their transferability of antibiotic resistance (AR) genes to pathogenic strains under in vivo, in vitro, and during food fermentation. For in vivo model, Albino Wistar rats were inoculated with 10¹⁰ CFU/g/ml of Enterococcus faecalis JH2-2 (recipient). After 7 days, either of two donors L. salivarius CH7-1E or L. reuteri [harbouring erythromycin and tetracycline resistance genes] were introduced at a concentration of 10⁹ CFU/ml daily for 1 week. Two days after donor introduction, there was a stable increase in the number of transconjugants in the animal faeces from 10² to 10³ CFU/g and presented erm(B), tet(M), tet(L) and tet(W) in their genome like donor strains. Similar observations were made with in vitro filter mating between CHS-1E, CH2-2 and CH7-1E and E. faecalis JH2-2 with transfer frequencies of 1 × 10^-4, 3.8 × 10^-3 and 2 × 10^-3 per donor cell respectively. With the results obtained in vivo and in vitro, the AR transferability of donor strains was estimated during food fermentation (chicken sausage, fermented milk or idli batter) with pathogenic recipient strains added as contaminants. At the end of mating period, phenotypic resistance to erythromycin and tetracycline in Listeria monocytogenes and Yersinia enterocolitica strains was observed. This study showed the ability of food borne Lactobacillus in diffusing their AR traits in diverse natural environments increasing their concern of AR dissemination in the food chain when used as food additives and/or probiotics.

Strain-Specific Quantification of Native Probiotic Bacillus spp. and Their Effect on Liver Function and Gut Microflora of Experimental Rats

Safety and efficacy was investigated for two candidate probiotic B. flexus MCC2427 and B. licheniformis MCC2512 via in vivo studies on albino Wistar rats. In acute toxicity assay, rats were fed with single dose of 10¹⁰ cfu mL^-1 of probiotics. The follow-up studies for next 14 days did not reveal any toxicity-related criteria indicating the non-toxicity nature of probiotics. In 90-day repeated dosage studies, the cultures were administered in three doses (10⁶, 10⁷, 10⁸ cfu mL^-1). Results showed no overt toxic effect and no drastic treatment-related changes pertaining to histopathology of vital organs. DNA fingerprinting indicated the lack of bacterial translocation. Superoxide dismutase and catalase activity indicated their antioxidant potential. Reduced serum cholesterol with improved HDL-cholesterol specified the cholesterol-reducing ability of the cultures, which was also apparent with increased excretion of cholic acid in feces. Both probiotic cultures positively altered the gut microbial environment, retained lactic acid bacterial effect, and simultaneously reduced pathogenic strains. A sensitive and rapid tool was developed using strain-specific qPCR primers, which facilitated appropriate estimation of test culture in feces. The data strongly advocate the safety of tested probiotics at levels used in the study.

Effective identification of Lactobacillus casei group species: genome-based selection of the gene mutL as the target of a novel multiplex PCR assay

Lactobacillus casei,Lactobacillus paracasei and Lactobacillusrhamnosus form a closely related taxonomic group (the L. casei group) within the facultatively heterofermentative lactobacilli. Strains of these species have been used for a long time as probiotics in a wide range of products, and they represent the dominant species of nonstarter lactic acid bacteria in ripened cheeses, where they contribute to flavour development. The close genetic relationship among those species, as well as the similarity of biochemical properties of the strains, hinders the development of an adequate selective method to identify these bacteria. Despite this being a hot topic, as demonstrated by the large amount of literature about it, the results of different proposed identification methods are often ambiguous and unsatisfactory. The aim of this study was to develop a more robust species-specific identification assay for differentiating the species of the L. casei group. A taxonomy-driven comparative genomic analysis was carried out to select the potential target genes whose similarity could better reflect genome-wide diversity. The gene mutL appeared to be the most promising one and, therefore, a novel species-specific multiplex PCR assay was developed to rapidly and effectively distinguish L. casei, L. paracasei and L. rhamnosus strains. The analysis of a collection of 76 wild dairy isolates, previously identified as members of the L. casei group combining the results of multiple approaches, revealed that the novel designed primers, especially in combination with already existing ones, were able to improve the discrimination power at the species level and reveal previously undiscovered intraspecific biodiversity.

Isolation of a novel alginate lyase-producing Bacillus litoralis strain and its potential to ferment Sargassum horneri for biofertilizer

Algae have long been used to augment plant productivity through their beneficial effects. Alginate oligosaccharide is believed to be one of the important components to enhance growth and crop yield. In this study, we isolated and characterized a Bacillus litoralis strain, named Bacillus M3, from decayed kelps. We further demonstrated that the M3 strain could secrete alginate lyase to degrade alginate. The crude enzyme exhibited the highest activity (33.74 U/mg) at pH 7.0 and 50°C. The M3 strain was also able to ferment the brown alga Sargassum horneri. Fermentation results revealed that a fermentation period of 8-12 hr was the best harvest time with the highest level of alginate oligosaccharides. Plant growth assay showed that the seaweed fermentation extract had an obvious promotion effect on root and seedling growth of Lycopersicon eseulentum L. Our results suggest that fermentation extract of Sargassum horneri by the novel strain of Bacillus litoralis M3 has significant development potential for biofertilizer production and agriculture application.

Discrimination and divergence among Lactobacillus plantarum-group (LPG) isolates with reference to their probiotic functionalities from vegetable origin

The present study was aimed to evaluate the diversity and probiotic properties of Lactobacillus plantarum-group cultures from vegetable origin. First, genotypic diversity of L. plantarum (n=34) was achieved by PCR of Random Amplified Polymorphic DNA and recA gene-specific multiplex PCR. The isolates were segregated into five groups namely, Lactobacillus pentosus, Lactobacillus paraplantarum, Lactobacillus arizonensis, Lactobacillus plantarum subsp. plantarum and argentoratensis. Further discrimination was achieved by restriction fragment length polymorphism of probiotic adhesion genes viz.fbp, mub and msa gene. As determined by nucleotide sequence analysis and bioinformatics Pfam database, the putative Fbp protein had only one FBP domain, whereas Mub protein had 8-10 MUB domain repeats. However, L. pentosus (except CFR MFT9), L. plantarum subsp. argentoratensis (except CFR MFT5) and L. arizonensis (except CFR MFT2) isolates gave no amplicon for the tested marker genes. Selected cultures (n=15) showed tolerance to simulated digestive fluids (20-85%), exhibited auto-aggregation (10-77%), cellular hydrophobicity (12-78%), and broad spectrum of anti-microbial activity. Concurrently, high adherence capacity to mucin was achieved for L. plantarum subsp. plantarum (MCC 2974 and CFR MFT1) and L. paraplantarum (MTCC 9483, MCC 2977, MCC 2978), which had an additional MUB domain repeat.

Screening, Characterization and In Vitro Evaluation of Probiotic Properties Among Lactic Acid Bacteria Through Comparative Analysis

The present work aimed to identify probiotic bacteria from healthy human infant faecal and dairy samples. Subsequently, an assay was developed to evaluate the probiotic properties using comparative genetic approach for marker genes involved in adhesion to the intestinal epithelial layer. Several in vitro properties including tolerance to biological barriers (such as acid and bile), antimicrobial spectrum, resistance to simulated digestive fluids and cellular hydrophobicity were assessed. The potential probiotic cultures were rapidly characterized by morphological, physiological and molecular-based methods [such as RFLP, ITS, RAPD and (GTG)5]. Further analysis by 16S rDNA sequencing revealed that the selected isolates belong to Lactobacillus, Pediococcus and Enterococcus species. Two cultures of non-lactic, non-pathogenic Staphylococcus spp. were also isolated. The native isolates were able to survive under acidic, bile and simulated intestinal conditions. In addition, these cultures inhibited the growth of tested bacterial pathogens. Further, no correlation was observed between hydrophobicity and adhesion ability. Sequencing of probiotic marker genes such as bile salt hydrolase (bsh), fibronectin-binding protein (fbp) and mucin-binding protein (mub) for selected isolates revealed nucleotide variation. The probiotic binding domains were detected by several bioinformatic tools. The approach used in the study enabled the identification of potential probiotic domains responsible for adhesion of bacteria to intestinal epithelial layer, which may further assist in screening of novel probiotic bacteria. The rapid detection of binding domains will help in revealing the beneficial properties of the probiotic cultures. Further, studies will be performed to develop a novel probiotic product which will contribute in food and feed industry.

Expression, purification, and characterization of a bifunctional 99-kDa peptidoglycan hydrolase from Pediococcus acidilactici ATCC 8042

Pediococcus acidilactici ATCC 8042 is a lactic acid bacteria that inhibits pathogenic microorganisms such as Staphylococcus aureus through the production of two proteins with lytic activity, one of 110 kDa and the other of 99 kDa. The 99-kDa one has high homology to a putative peptidoglycan hydrolase (PGH) enzyme reported in the genome of P. acidilactici 7_4, where two different lytic domains have been identified but not characterized. The aim of this work was the biochemical characterization of the recombinant enzyme of 99 kDa. The enzyme was cloned and expressed successfully and retains its activity against Micrococcus lysodeikticus. It has a higher N-acetylglucosaminidase activity, but the N-acetylmuramoyl-L-alanine amidase can also be detected spectrophotometrically. The protein was then purified using gel filtration chromatography. Antibacterial activity showed an optimal pH of 6.0 and was stable between 5.0 and 7.0. The optimal temperature for activity was 60 °C, and all activity was lost after 1 h of incubation at 70 °C. The number of strains susceptible to the recombinant 99-kDa enzyme was lower than that susceptible to the mixture of the 110- and 99-kDa PGHs of P. acidilactici, a result that suggests synergy between these two enzymes. This is the first PGH from LAB that has been shown to possess two lytic sites. The results of this study will aid in the design of new antibacterial agents from natural origin that can combat foodborne disease and improve hygienic practices in the industrial sector.

Effect of storage temperature on the microbial composition of ready-to-use vegetables

Four different salad preparations were investigated from microbiological point of view: two were packaged in air and two under Modified Atmosphere. The samples were stored at 4 and 10 °C, and analysed at established times. Total bacterial count (TBC) was taken as the most relevant index to define their hygiene and quality at both temperatures. Lactic acid bacteria, yeasts and moulds were found only occasionally. In general, the most important factor was the packaging technique: TBC was lower when the product is packed under modified conditions. The packaging technique also influences the microbial population: Gram-negative aerobic rods are dominant in air-packaged products, whilst the presence of Enterobacteriaceae becomes important in salads packaged under Modified Atmosphere. Pseudomonas fluorescens, with all its biovars, was the most frequently found species amongst the aerobic isolates, whilst for the Enterobacteriaceae strains, there was no dominant species.

Microbial ecology of sourdough fermentations: diverse or uniform?

Sourdough is a specific and stressful ecosystem inhabited by yeasts and lactic acid bacteria (LAB), mainly heterofermentative lactobacilli. On the basis of their inocula, three types of sourdough fermentation processes can be distinguished, namely backslopped ones, those initiated with starter cultures, and those initiated with a starter culture followed by backslopping. Typical sourdough LAB species are Lactobacillus fermentum, Lactobacillus paralimentarius, Lactobacillus plantarum, and Lactobacillus sanfranciscensis. Typical sourdough yeast species are Candida humilis, Kazachstania exigua, and Saccharomyces cerevisiae. Whereas region specificity is claimed in the case of artisan backslopped sourdoughs, no clear-cut relationship between a typical sourdough and its associated microbiota can be found, as this is dependent on the sampling, isolation, and identification procedures. Both simple and very complex consortia may occur. Moreover, a series of intrinsic and extrinsic factors may influence the composition of the sourdough microbiota. For instance, an influence of the flour (type, quality status, etc.) and the process parameters (temperature, pH, dough yield, backslopping practices, etc.) occurs. In this way, the presence of Lb. sanfranciscensis during sourdough fermentation depends on specific environmental and technological factors. Also, Triticum durum seems to select for obligately heterofermentative LAB species. Finally, there are indications that the sourdough LAB are of intestinal origin.

Potential of marine lactic acid bacteria to ferment Sargassum sp. for enhanced anticoagulant and antioxidant properties

AIM

To evaluate the suitability of marine lactic acid bacteria (LAB) as starter cultures for Sargassum sp. fermentation to enhance its antioxidant and anticoagulation activity.

METHODS AND RESULTS

LAB isolated from marine source were characterized for their ability to utilize seaweed as a sole carbon source and applied to Sargassum fermentation. Fermentation period was optimized by monitoring the fermented sample at regular interval for a period of 18 days. Results revealed that a fermentation period of 12 days was effective with maximum culture viability and other desirable characteristics such as pH, total titratable acidity, total and reducing sugars. Under optimum fermentation period, the sample fermented with P1-2CB-w1 (Enterococcus faecium) exhibited maximum anticoagulation activity and antioxidant activity.

CONCLUSIONS

The study reveals a novel well-defined starter culture from marine origin intended for seaweed fermentation for recovery of bioactive molecules.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study provides information for the enhancement of bioactive molecules in an eco-friendly manner and also paves a way towards the development of wide range of seaweed functional foods.

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.

Presence of erythromycin and tetracycline resistance genes in lactic acid bacteria from fermented foods of Indian origin

Lactic acid bacteria (LAB) resistant to erythromycin were isolated from different food samples on selective media. The isolates were identified as Enterococcus durans, Enterococcus faecium, Enterococcus lactis, Enterococcus casseliflavus, Lactobacillus salivarius, Lactobacillus reuteri, Lactobacillus plantarum, Lactobacillus fermentum, Pediococcus pentosaceus and Leuconostoc mesenteroides. Of the total 60 isolates, 88 % harbored the ermB gene. The efflux gene msrA was identified in E. faecium, E. durans, E. lactis, E. casseliflavus, P. pentosaceus and L. fermentum. Further analysis of the msrA gene by sequencing suggested its homology to msrC. Resistance to tetracycline due to the genes tetM, tetW, tetO, tetK and tetL, alone or in combination, were identified in Lactobacillus species. The tetracycline efflux genes tetK and tetL occurred in P. pentosaceus and Enterococcus species. Since it appeared that LAB had acquired these genes, fermented foods may be a source of antibiotic resistance.

Novel whole-cell Reporter Assay for Stress-Based Classification of Antibacterial Compounds Produced by Locally Isolated Bacillus spp

Reporter bacteria are beneficial for the rapid and sensitive screening of cultures producing peptide antibiotics, which can be an addition or alternative to the established antibiotics. This study was carried out to validate the usability of specific reporter strains for the target mediated identification of antibiotics produced by native Bacillus spp. isolated from different food sources. During preliminary classification, cell wall stress causing Bacillus isolates were screened by using reporter strain Bacillus subtilis BSF2470. The isolates which induced cell wall stress were further characterized for their specific mode of action by using other B. subtilis reporter strains (TMB 488, TMB 299 and TMB 279). The isolate B. licheniformis N12 was found to produce bacitracin confirmed by the response to reporter strain B. subtilis TMB 279 and by putative identification of bacitracin biosynthetic loci. The other isolate B. subtilis EC1 also induced B. subtilis TMB 279, but does not possess the bacitracin gene cluster indicating that it can be a novel, bacitracin like antibiotic. The different but related subsets of peptide antibiotics that bind the pyrophosphate moiety of the lipid carrier of cell wall biosynthesis can be identified using this whole cell based reporter strains.

Phenotypic and Genotypic Characterization of Lactic Acid Bacteria Isolated from Artisanal Italian Goat Cheese

The lactic acid bacteria community in traditional goat cheese produced in three dairies in Valsesia (Piemonte, Italy) was studied at different steps of the manufacturing process. These cheeses were produced from raw milk without starter bacteria, and no protocol was followed during the manufacturing process. Three hundred thirty-two isolates were characterized and grouped by results of both morphophysiological tests and random amplification of polymorphic DNA plus PCR analysis. Bacteria were identified by partial sequencing of the 16S rRNA gene. Lactococci were the dominant lactic acid bacteria in raw milk. Their initial numbers ranged from 5 to 7 log CFU ml−1. Their levels increased during manufacturing and decreased during ripening. The growth trend for enterococci was comparable to that of lactococci, although enterococci counts were lower. Lactococcus lactis subsp. cremoris, Lactococcus garviae, and Enterococcus faecalis were the most frequently isolated species during goat cheese manufacturing, whereas the highest numbers of Enterococcus (E. faecium, E. durans, E. gilvus, and E. casseliflavus) were isolated with the greatest frequency from ripened cheese samples. Occasionally, Leuconostoc mesenteroides, Leuconostoc lactis, and Lactobacillus paraplantarum also were isolated.

Diversity of lactic acid bacteria from Hussuwa, a traditional African fermented sorghum food

The diversity of lactic acid bacteria associated with Hussuwa fermentation, a Sudanese fermented sorghum food, was studied using a polyphasic taxonomical approach. Predominant strains could be well characterised based on a combination of phenotypic tests and genotypic methods such as ARDRA, rep-PCR and RAPD-PCR, as well as 16S rRNA gene sequencing of representative strains. Thus, the majority (128 of 220, 58.3%) of strains exhibited phenotypic properties typical of heterofermentative lactobacilli and of these, 100 strains were characterised more closely using the genotyping methods. The majority (97/100) strains could be characterised as Lactobacillus fermentum strains. Seventy-two of 220 strains (32.7%) showed phenotypic properties that are characteristic of pediococci. Of 41 selected strains investigated by genotyping techniques, 38 (92.7%) could be characterised as Pediococcus acidilactici strains, while three (7.3%) could be characterised as Pediococcus pentosaceus strains. The Hussuwa fermentation thus appears to be dominated by L. fermentum strains and P. acidilactici strains. For this reason, we selected representative and predominant strains as potential starter cultures for Hussuwa fermentation. These strains, L. fermentum strains BFE 2442 and BFE 2282 and P. acidilactici strain BFE 2300, were shown on the basis of RAPD-PCR fingerprinting to predominate in a model fermentation when used as starter cultures inoculated at 1 x 10(6) CFU/g and to lower the pH of the fermentation to below pH 4.0 within 48 h. These cultures should be studied for further development as starter preparations in pilot scale studies in actual field fermentations.

Pediocins: The bacteriocins of Pediococci. Sources, production, properties and applications

Class IIa bacteriocins from lactic acid bacteria are small, cationic proteins with antilisterial activity. Within this class, the pediocins are those bacteriocins that share a highly conserved hydrophilic and charged N-terminal part harboring the consensus sequence -YGNGV- and a more variable hydrophobic and/or amphiphilic C-terminal part. Several pediocins have been isolated and characterized. Despite the structural similarities, their molecular weight varies, as well as their spectrum of antimicrobial activity. They exhibit important technological properties, e.g. thermostability and retaining of activity at a wide pH range, which along with the bactericidal action against Gram-positive food spoilage and pathogenic bacteria, make them an important class of biopreservatives. Much new information regarding the pediocins has emerged during the last years. In this review, we summarize and discuss all the available information regarding the sources of pediocins, the characteristics of their biosynthesis and production in fermentation systems, the characteristics of the known pediocin molecules, and their antibacterial action. The advances made by genetic engineering in improving the features of pediocins are also discussed, as well as their perspectives for future applications.

Processing of as-48ABC RNA in AS-48 enterocin production by Enterococcus faecalis

Enterocin AS-48 production and immunity characters are encoded by 10 genes (as-48ABCC(1)DD(1)EFGH) of the pMB2 plasmid from the Enterococcus faecalis S-48 strain. Among these, as-48A, encoding the AS-48 peptide, and the as-48BC genes constitute a cluster required for AS-48 biogenesis and full immunity. In this study, the levels of expression of this cluster have been altered by insertion and site-directed mutagenesis as well as by expression coupled to trans complementation. Phenotypic studies of the mutants have indicated cotranscription of the three genes and revealed that the inactivation of as-48B prevents the production of AS-48, thus confirming its essentiality in AS-48 biogenesis. These studies have also supported the involvement of as-48C in enterocin immunity. In addition, they established that the intergenic region between the as-48A and as-48B genes is decisive for AS-48 expression, since a 3-bp substitution, which should disrupt a potential 47-nucleotide complex secondary structure, resulted in a hypoproducing phenotype. Transcriptional analyses of the E. faecalis wild-type and mutant strains supports the possibility that the as-48ABC genes are transcribed from the P(A) promoter located upstream of as-48A. Moreover, analysis and bioinformatic predictions of RNA folding indicate that as-48ABC mRNA is processed at the secondary structure located between as-48A and as-48B. Thus, synthesis of the AS-48 peptide appears to be controlled at the posttranscriptional level and is uncoupled from as-48BC translation. This mechanism of genetic regulation has not been previously described for the regulation of bacteriocin expression in enterococci.