Bacteriocin-mediated inhibition of Clostridium botulinum spores by lactic acid bacteria at refrigeration and abuse temperatures

The Complex Role of Lactic Acid Bacteria in Food Detoxification

Toxic ingredients in food can lead to serious food-related diseases. Such compounds are bacterial toxins (Shiga-toxin, listeriolysin, Botulinum toxin), mycotoxins (aflatoxin, ochratoxin, zearalenone, fumonisin), pesticides of different classes (organochlorine, organophosphate, synthetic pyrethroids), heavy metals, and natural antinutrients such as phytates, oxalates, and cyanide-generating glycosides. The generally regarded safe (GRAS) status and long history of lactic acid bacteria (LAB) as essential ingredients of fermented foods and probiotics make them a major biological tool against a great variety of food-related toxins. This state-of-the-art review aims to summarize and discuss the data revealing the involvement of LAB in the detoxification of foods from hazardous agents of microbial and chemical nature. It is focused on the specific properties that allow LAB to counteract toxins and destroy them, as well as on the mechanisms of microbial antagonism toward toxigenic producers. Toxins of microbial origin are either adsorbed or degraded, toxic chemicals are hydrolyzed and then used as a carbon source, while heavy metals are bound and accumulated. Based on these comprehensive data, the prospects for developing new combinations of probiotic starters for food detoxification are considered.

Oligonol, a Low-molecular Weight Polyphenol Extracted from Lychee Fruit, Modulates Cholesterol Metabolism in Rats within a Short Period

There is growing research interest in the hypocholesterolemic effect of various food components such as polyphenols. In this study, we examined the effects of oligonol-a low-molecular weight polyphenol extracted from lychee fruit-on cholesterol metabolism in rats under short-term administration. Administration of oligonol for 3 days significantly increased cecum weight and decreased cecal n-butyric acid concentrations in rats. Oligonol also significantly lowered the levels of hepatic cholesterol and increased the levels of total neutral steroids excreted in the feces. It also increased fecal β-muricholic acid significantly, whereas the levels of total acidic steroids remained unchanged. Gene expression of hepatic CYP7A1 (cytochrome P450 family 7 subfamily A member 1) significantly increased following the administration of oligonol. This increase could be ascribed to changes in the expression of farnesoid X receptor, small heterodimer partner, and fibroblast growth factor 15 in ileum. Our data suggest that oligonol induces hypocholesterolemic effects through the inhibition of biliary cholesterol absorption from the intestine and the upregulation of cholesterol catabolism in rats even following short-term administration. Therefore, oligonol may be an important food component for reducing cholesterol level.

Antibacterial and antifungal activity of crude and freeze-dried bacteriocin-like inhibitory substance produced by Pediococcus pentosaceus

Pediococcus pentosaceus LBM 18 has shown potential as producer of an antibacterial and antifungal bacteriocin-like inhibitory substance (BLIS). BLIS inhibited the growth of spoilage bacteria belonging to Lactobacillus, Enterococcus and Listeria genera with higher activity than Nisaplin used as control. It gave rise to inhibition halos with diameters from 9.70 to 20.00 mm, with Lactobacillus sakei being the most sensitive strain (13.50-20.00 mm). It also effectively suppressed the growth of fungi isolated from corn grain silage for up to 25 days and impaired morphology of colonies by likely affecting fungal membranes. These results point out that P. pentosaceus BLIS may be used as a new promising alternative to conventional antibacterial and antifungal substances, with potential applications in agriculture and food industry as a natural bio-controlling agent. Moreover, cytotoxicity and cell death induction tests demonstrated cytotoxicity and toxicity of BLIS to human colon adenocarcinoma Caco-2cells but not to peripheral blood mononuclear cells, with suggests possible applications of BLIS also in medical-pharmaceutical applications.

Effects of Citrus sinensis Essential Oil and Intrinsic and Extrinsic Factors on the Growth and ToxinProducing Ability of Clostridium botulinum Type A

Background: Considering the high fatality of botulism, the control of Clostridium botulinum and its neurotoxins has clinical importance. In this regard, using chemical preservatives, natural essential oils (Eos), and changes in the growth predisposing factors of bacteria are suitable methods to control the growth and toxin producing of C. botulinum in foods. Objective: The current survey was done to assess the effects of Citrus sinensis EO and intrinsic and extrinsic factors on the growth and toxin producing of C. botulinum type A. Materials and Methods: In this experiment with a factorial design, C. sinensis EO (0.0%, 0.015%, 0.03%, and 0.045%), nisin (0, 500, and 1500 IU/mL), nitrite (0, 20, and 60 ppm), pH (5.5 and 6.5), storage temperature (25 and 35° C), and sodium chloride (NaCl, 0.5% and 3%) were used to assess bacterial growth in the brain heart infusion medium. Finally, the mouse bioassay method was also used to assess toxicity. Results: Clostridium sinensis EO with a concentration of 0.045%, as well as the reduction of pH and temperature could significantly delay the growth of bacteria (P≤0.05) in contrast to the use of NaCl and nisin alone. However, all concentrations of sodium chloride (NaCl), nisin, and C. sinensis EO (< 0.045%) in interaction with each other, especially in combination with nitrite, showed good synergistic effects. Conclusion: These results suggested that using certain concentrations of C. sinensis EO and nisin, along with other suboptimal factors caused a significant decrease in the nitrite contents of foods with a significant reduction in the growth and toxin-producing ability of C. botulinum.

Livers provide a reliable matrix for real-time PCR confirmation of avian botulism

Diagnosis of avian botulism is based on clinical symptoms, which are indicative but not specific. Laboratory investigations are therefore required to confirm clinical suspicions and establish a definitive diagnosis. Real-time PCR methods have recently been developed for the detection of Clostridium botulinum group III producing type C, D, C/D or D/C toxins. However, no study has been conducted to determine which types of matrices should be analyzed for laboratory confirmation using this approach. This study reports on the comparison of different matrices (pooled intestinal contents, livers, spleens and cloacal swabs) for PCR detection of C. botulinum. Between 2013 and 2015, 63 avian botulism suspicions were tested and 37 were confirmed as botulism. Analysis of livers using real-time PCR after enrichment led to the confirmation of 97% of the botulism outbreaks. Using the same method, spleens led to the confirmation of 90% of botulism outbreaks, cloacal swabs of 93% and pooled intestinal contents of 46%. Liver appears to be the most reliable type of matrix for laboratory confirmation using real-time PCR analysis.

The influence of glyphosate on the microbiota and production of botulinum neurotoxin during ruminal fermentation

The aim of the present study is to investigate the impact of glyphosate on the microbiota and on the botulinum neurotoxin (BoNT) expression during in vitro ruminal fermentation. This study was conducted using two DAISY(II)-incubators with four ventilated incubation vessels filled with rumen fluid of a 4-year-old non-lactating Holstein-Friesian cow. Two hundred milliliter rumen fluid and 800 ml buffer solution were used with six filter bags containing 500 mg concentrated feed or crude fiber-enriched diet. Final concentrations of 0, 1, 10, and 100 µg/ml of glyphosate in the diluted rumen fluids were added and incubated under CO2-aerated conditions for 48 h. The protozoal population was analyzed microscopically and the ruminal flora was characterized using the fluorescence in situ hybridization technique. Clostridium botulinum and BoNT were quantified using most probable number and ELISA, respectively. Results showed that glyphosate had an inhibitory effect on select groups of the ruminal microbiota, but increased the population of pathogenic species. The BoNT was produced during incubation when inoculum was treated with high doses of glyphosate. In conclusion, glyphosate causes dysbiosis which favors the production of BoNT in the rumen. The global regulations restrictions for the use of glyphosate should be re-evaluated.

Invasive slug populations (Arion vulgaris) as potential vectors for Clostridium botulinum

Background

Norwegian meadows, including those for silage production, are recently found heavily invaded by the slug Arion vulgaris in exposed areas. As a consequence, large numbers of slugs might contaminate grass silage and cause a possible threat to animal feed quality and safety. It is well known that silage contaminated by mammalian or avian carcasses can lead to severe outbreaks of botulism among livestock. Invertebrates, especially fly-larvae (Diptera), are considered important in the transfer of Clostridium botulinum type C and its toxins among birds in wetlands. C. botulinum form highly resistant spores that could easily be consumed by the slugs during feeding. This study aimed to determine whether Arion vulgaris could hold viable C. botulinum and enrich them, which is essential knowledge for assessing the risk of botulism from slug-contaminated silage. Slug carcasses, slug feces and live slugs were tested by a quantitative real-time PCR (qPCR) method after being fed ≅ 5.8 × 10⁴ CFU C. botulinum type C spores/slug.

Results

Low amounts of C. botulinum were detected by qPCR in six of 21 slug carcasses with an even spread throughout the 17 day long experiment. Declining amounts of C. botulinum were excreted in slug feces up to day four after the inoculated feed was given. C. botulinum was only quantified the first two days in the sampling of live slugs. The viability of C. botulinum was confirmed for all three sample types (slug carcasses, slug feces and live slugs) by visible growth in enrichment media combined with obtaining a higher quantification cycle (Cq) value than from the non-enriched samples.

Conclusions

Neither dead nor live invasive Arion vulgaris slugs were shown to enrich Clostridium botulinum containing the neurotoxin type C gene in this study. Slugs excreted viable C. botulinum in their feces up to day four, but in rapidly decreasing numbers. Arion vulgaris appear not to support enrichment of C. botulinum type C.

New targets in the search for preventive and therapeutic agents for botulism

Botulism is a severe neuroparalytic disease resulting from exposure to one of the most poisonous toxins to humans. Because of this high potency and the use of toxins as biological weapons, botulism is a public health concern and each case represents an emergency. Current therapy involves respiratory supportive care and anti-toxins administration. As a preventive measure, vaccination against toxins represents an effective strategy but is undesirable due the rarity of botulism and the effectiveness of toxins in treating several neuromuscular disorders. This paper summarizes the current issues in botulism treatment and prevention, highlighting the challenge for future researches.

Relationship between gastrointestinal dysbiosis and Clostridium botulinum in dairy cows

The gastrointestinal tract is a balanced ecosystem that can get out of balance and predisposed to clostridial diseases or other pathological conditions. The objective of the present study was to evaluate the gut microbiota in dairy cows suffering from chronic botulism. Cows were investigated for Clostridium (C.) botulinum in faeces and rumen fluids. In order to study the relationship between botulism and gastrointestinal microbiota, faeces and rumen fluid were tested for bacterial composition using conventional microbiological culture techniques and fluorescence in situ hybridization (FISH). Protozoa were analyzed in rumen fluid microscopically. The presence of C. botulinum was associated with specific changes in the faecal microbiota, especially a significant reduction of total aerobic bacteria, total anaerobic bacteria, enterococci, Clostridium perfringens and yeast and fungi. Also C. botulinum positive rumen fluid had significantly more Bacteroides spp., C. histolyticum group, Alfa- proteobacteria, Gammaproteobacteria, and sulfate-reducing bacteria; as well as significantly fewer Euryaracheota, and the protozoa Epidinium spp. Dasytricha spp., Diplodiniinae spp. and Ophryoscolex spp. In conclusion, C. botulinum is common in dairy cows in Germany but the incidence of botulism is associated with microbial changes and composition in the gastrointestinal tract. Bacteria, yeast and protozoa appear to be crucial in the colonization process; however, the chronology of these events and role of each microbial group needs further evaluation.

Effects of 8 chemical and bacterial additives on the quality of corn silage

This project aimed to evaluate the effects 8 additives on the fermentation, dry matter (DM) losses, nutritive value, and aerobic stability of corn silage. Corn forage harvested at 31% DM was chopped (10mm) and treated with (1) deionized water (control); (2) Buchneri 500 (BUC; 1×10(5) cfu/g of Pediococcus pentosaceus 12455 and 4×10(5) cfu/g of Lactobacillus buchneri 40788; Lallemand Animal Nutrition, Milwaukee, WI); (3) sodium benzoate (BEN; 0.1% of fresh forage); (4) Silage Savor acid mixture (SAV: 0.1% of fresh forage; Kemin Industries Inc., Des Moines, IA); (5) 1×10(6) cfu/g of Acetobacter pasteurianus-ATCC 9323; (6) 1×10(6) cfu/g of Gluconobacter oxydans-ATCC 621; (7) Ecosyl 200T (1×10(5) cfu/g of Lactobacillus plantarum MTD/1; Ecosyl Products Inc., Byron, IL); (8) Silo-King WS (1.5×10(5) cfu/g of L. plantarum, P. pentosaceus and Enterococcus faecium; Agri-King, Fulton, IL); and (9) Biomax 5 (BIO; 1×10(5) cfu/g of L. plantarum PA-28 and K-270; Chr. Hansen Animal Health and Nutrition, Milwaukee, WI). Treated forage was ensiled in quadruplicate in mini silos at a density of 172 kg of DM/m(3) for 3 and 120 d. After 3 d of ensiling, the pH of all silages was below 4 but ethanol concentrations were least in BEN silage (2.03 vs. 3.24% DM) and lactic acid was greatest in SAV silage (2.97 vs. 2.51% DM). Among 120-d silages, additives did not affect DM recovery (mean=89.8% ± 2.27) or in vitro DM digestibility (mean=71.5% ± 0.63). The SAV silage had greater ammonia-N (0.85 g/kg of DM) and butyric acid (0.22 vs. 0.0% DM) than other treatments. In contrast, BEN and Silo-King silages had the least ammonia-N concentration and had no butyric acid. The BEN and A. pasteurianus silages had the lowest pH (3.69) and BEN silage had the least ethanol (1.04% DM) and ammonia nitrogen (0.64 g/kg DM) concentrations, suggesting that fermentation was more extensive and protein degradation was less in BEN silages. The BUC and BIO silages had greater acetic acid concentrations than control silages (3.19 and 3.19 vs. 2.78% DM), but yeast counts did not differ. Aerobic stability was increased by 64% by BUC (44.30 h) and by 35% by BEN (36.49 h), but other silages had similar values (27.0±1.13 h).

Antibacterial efficacy of Nisin, Pediocin 34 and Enterocin FH99 against Listeria monocytogenes and cross resistance of its bacteriocin resistant variants to common food preservatives

Antilisterial efficiency of three bacteriocins, viz, Nisin, Pediocin 34 and Enterocin FH99 was tested individually and in combination against Listeria mononcytogenes ATCC 53135. A greater antibacterial effect was observed when the bacteriocins were combined in pairs, indicating that the use of more than one LAB bacteriocin in combination have a higher antibacterial action than when used individually. Variants of Listeria monocytogenes ATCC 53135 resistant to Nisin, Pediocin 34 and Enterocin FH99 were developed. Bacteriocin cross-resistance of wild type and their corresponding resistant variants were assessed and results showed that resistance to a bacteriocin may extend to other bacteriocins within the same class. Resistance to Pediocin 34 conferred cross resistance to Enterocin FH 99 but not to Nisin. Similarly resistance to Enterocin FH99 conferred cross resistance to Pediocin 34 but not to Nisin. Also, the sensitivity of Nisin, Pediocin 34 and Enterocin FH99 resistant variants of Listeria monocytogenes to low pH, salt, sodium nitrite, and potassium sorbate was assayed in broth and compared to the parental wild-type strain. The Nisin, Pediocin 34 and Enterocin FH99 resistant variants did not have intrinsic resistance to low pH, sodium chloride, potassium sorbate, or sodium nitrite. In no case were the bacteriocin resistant Listeria monocytogenes variants examined were more resistant to inhibitors than the parental strains.

Glyphosate suppresses the antagonistic effect of Enterococcus spp. on Clostridium botulinum

During the last 10-15 years, an increase of Clostridium botulinum associated diseases in cattle has been observed in Germany. The reason for this development is currently unknown. The normal intestinal microflora is a critical factor in preventing intestinal colonisation by C. botulinum as shown in the mouse model of infant botulism. Numerous bacteria in the gastro-intestinal tract (GIT) produce bacteriocines directed against C. botulinum and other pathogens: Lactic acid producing bacteria (LAB) such as lactobacilli, lactococci and enterococci, generate bacteriocines that are effective against Clostridium spp. A reduction of LAB in the GIT microbiota by ingestion of strong biocides like glyphosate could be an explanation for the observed increase in levels of C. botulinum associated diseases. In the present paper, we report on the toxicity of glyphosate to the most prevalent Enterococcus spp. in the GIT. Ingestion of this herbicide could be a significant predisposing factor that is associated with the increase in C. botulinum mediated diseases in cattle.

Botulism challenge studies of a modified atmosphere package for fresh mussels: inoculated pack studies

A series of botulism challenge studies were performed to determine the possibility of production of botulinum toxin in mussels (Mytilus edulis) held under a commercial high-oxygen (60 to 65% O(2)), modified atmosphere packaging (MAP) condition. Spore mixtures of six strains of nonproteolytic Clostridium botulinum were introduced into mussel MAP packages receiving different packaging buffers with or without the addition of lactic acid bacteria. Dye studies and package flipping trials were conducted to ensure internalization of spores by packed mussels. Inoculated mussel packages were stored at normal (4°C) and abusive (12°C) temperatures for 21 and 13 days, respectively, which were beyond the packaged mussels' intended shelf life. Microbiological and chemical analyses were conducted at predetermined intervals (a total of five sampling times at each temperature), including total aerobic plate counts, C. botulinum counts, lactic acid bacterial counts, package headspace gas composition, pH of packaging buffer and mussel meat, and botulinum toxin assays of packaging buffer and mussel meat. Results revealed that C. botulinum inoculated in fresh mussels packed under MAP packaging did not produce toxin, even at an abusive storage temperature and when held beyond their shelf life. No evidence was found that packaging buffers or gas composition influenced the lack of botulinum toxin production in packed mussels.

Common mechanistic action of bacteriocins from lactic Acid bacteria

The influence of four bacteriocins from lactic acid bacteria on the proton motive force (PMF) of sensitive organisms was investigated. Pediocin PA-1 (20 mug/ml) and leuconocin S (48.5 mug/ml) mediated total or major PMF dissipation of energized Listeria monocytogenes Scott A cells in a concentration-dependent manner, as has been shown for nisin. Lactacin F (13.5 mug/ml) caused 87% PMF depletion of energized Lactobacillus delbrueckii ATCC 4797 cells, also in a concentration-dependent fashion. The energy requirements for the activity of these four bacteriocins were determined by using the ionophores nigericin and valinomycin to carry out partial and specific deenergization of the target organisms. Pediocin PA-1, leuconocin S, and lactacin F acted in an energy-independent manner, whereas the activity of nisin was confirmed to be energy dependent. These results together with published reports on other bacteriocins suggest that the bacteriocins of lactic acid bacteria share a common mechanism, the depletion of PMF.

Bacteriocins from Lactobacillus plantarum - production, genetic organization and mode of action: produção, organização genética e modo de ação

Bacteriocins are biologically active proteins or protein complexes that display a bactericidal mode of action towards usually closely related species. Numerous strains of bacteriocin producing Lactobacillus plantarum have been isolated in the last two decades from different ecological niches including meat, fish, fruits, vegetables, and milk and cereal products. Several of these plantaricins have been characterized and the aminoacid sequence determined. Different aspects of the mode of action, fermentation optimization and genetic organization of the bacteriocin operon have been studied. However, numerous of bacteriocins produced by different Lactobacillus plantarum strains have not been fully characterized. In this article, a brief overview of the classification, genetics, characterization, including mode of action and production optimization for bacteriocins from Lactic Acid Bacteria in general, and where appropriate, with focus on bacteriocins produced by Lactobacillus plantarum, is presented.

Use of microbial antagonism to reduce pathogen levels on produce and meat products: a review

Lactic acid bacteria (LAB) are often utilized to control food-borne pathogens on produce and on cooked, fermented, or refrigerated meats. Most research to date has focused on the inhibition of Listeria monocytogenes, Escherichia coli O157:H7, Salmonella, Clostridium botulinum, and spoilage microorganisms. LAB are excellent candidates for reducing pathogen levels on foods because they inhibit the growth of these microorganisms through various mechanisms without causing unacceptable sensory changes. This review provides an up-to-date look at research directed at maximizing the use of LAB by selecting the most appropriate strains, by learning how to apply them to foods most effectively, and by gaining an understanding of the mechanism by which they inhibit pathogens.Key words: bacterial competition, lactic acid bacteria, food-borne pathogens, meat products, produce.

Hazard and control of group II (non-proteolytic) Clostridium botulinum in modern food processing

Group II (non-proteolytic) Clostridium botulinum poses a safety hazard in modern food processing, which consists of mild pasteurization treatments, anaerobic packaging, extended shelf lives and chilled storage. The high risk is reflected in the relatively large number of botulism cases due to group II C. botulinum in commercially produced foods during the past decades. Because of the high prevalence of group II C. botulinum in the environment, food raw materials may carry spores. Although group II spores are less heat-resistant than group I (proteolytic) spores, they can tolerate the heat treatments employed in the chilled food industry. Some food components may actually provide spores with protection from heat. Spore heat resistance should therefore be investigated for each food in order to determine the efficiency of industrial heat treatments. Group II strains are psychrotrophic and thus they are able to grow at refrigeration temperatures. Anaerobic packages and extended shelf lives provide C. botulinum with favourable conditions for growth and toxin formation. As the use of salt and other preservatives in these foods is limited, microbiological safety relies mainly on refrigerated storage. This sets great challenges on the production of chilled packaged foods. To ensure the safety of these foods, more than one factor should safeguard against botulinal growth and toxin production.

Changes in fatty acids and microbial populations of pork inoculated with two biopreservative strains

Meat surface fermentation has been reported as an efficient method to reduce undesirable microbial population of this food commodity in tropical areas with high ambient temperatures and humidity. However, in order to efficiently apply this method, growth of biopreservative strains and changes in the meat substrate should be studied. Changes in long-chain fatty acids as well as pH and microbial growth (lactic acid bacteria and enterobacteria) were studied in pork inoculated with two biopreservative strains (Lactobacillus alimentarius and Staphylococcus carnosus) and stored at 4 and 20 °C. Both tested strains produced more than 6 mg lactic acid/g tissue, however, S. carnosus was more efficient in reducing enterobacteria populations at 20 °C. No significant increase in long-chain fatty acid concentration in samples stored at 4 °C was observed but there was a rapid increase of free fatty acids when stored at 20 °C.

Inhibition of nonproteolytic Clostridium botulinum with lactic acid bacteria and their bacteriocins at refrigeration temperatures

Nonproteolytic Clostridium botulinum (strains 17B, Beluga, and 202F) was found to be inhibited by Lactobacillus, Lactococcus, Streptococcus, and Pediococcus species in tests by the spot-on-the-lawn simultaneous-antagonism method at 10, 15, and 25 degrees C. C. botulinum 17B was the most resistant strain. Inhibition zone size increased with decreasing incubation temperature. Six strains of Lactobacillus acidophilus and seven strains of bifidobacteria failed to produce an inhibition zone on buffered reinforced clostridium Prussian blue agar seeded with spores of any of the selected C. botulinum strains. C. botulinum 17B was sensitive to 50 to 100 IU of nisin per ml and to 10 to 20 AU of pediocin A per ml.

Microbial antagonists of foodborne pathogens on fresh, minimally processed vegetables

On many types of raw or minimally processed foods, the bacterial microbiota is often composed of mixed species. The activities of one bacterial species may influence the growth and activities of others that are present. The objective of this project was to evaluate the microbial composition of fresh and minimally processed vegetables to determine if naturally occurring bacteria on produce are competitive with or antagonistic to potentially encountered pathogens. Naturally occurring bacteria were obtained from ready-to-eat salad vegetables on four occasions to allow for seasonal variation. Minimally processed vegetables were sampled at various stages in their processing from raw vegetables to packaged products. Some portions were analyzed microbiologically within 24 h, while other portions were stored refrigerated and analyzed after 72 h. Microbiological analysis was conducted for bacterial enumeration and to obtain isolates. An agar spot method was used to screen isolates for antimicrobial activity against Staphylococcus aureus ATCC 27664, Escherichia coli O157:H7 E009, Listeria monocytogenes LCDC 81-861, and Salmonella Montevideo. Of the 1,180 isolates screened for inhibitory activity, 37 (3.22%) were found to have various degrees of inhibitory activity against at least one test pathogen. Many isolates showed inhibitory activity against all four pathogens. The isolates with the most extensive inhibition were removed from finished lettuce piece shreds. Of the 37 inhibitory isolates, 34 (91.9%) were gram negative. All isolates with inhibitory activity are able to multiply at both 4 and 10 degrees C.

Influence of pH, temperature and culture media on the growth and bacteriocin production by vaginal Lactobacillus salivarius CRL 1328

AIMS

To study the influence of pH, temperature and culture medium on the growth and bacteriocin production by vaginal Lactobacillus salivarius subsp. salivarius CRL 1328.

METHODS AND RESULTS

The study was performed using a complete factorial experimental design. Lactobacillus salivarius was cultivated in LAPTg and MRS broths, adjusted to specific initial pH, and at different temperatures of incubation. The growth, which was evaluated by the Gompertz model, was higher in MRS broth than in LAPTg broth. The initial pH of the culture medium and the temperature had a dramatic effect on the production of bacteriocin. The optimal conditions for bacteriocin production were different to those for optimal growth. The decrease in the pH of the culture medium was parallel to the growth; pH had similar final values in both the MRS and the LAPTg broths.

CONCLUSIONS

The optimal growth conditions were recorded in MRS broth, with an initial pH of 6.5 and a temperature of 37 degrees C. The maximum bacteriocin activity was obtained in LAPTg after 6 h at 37 degrees C, and at an initial pH of 6.5 or 8.0.

SIGNIFICANCE AND IMPACT OF THE STUDY

The application of a complete factorial design, and the evaluation of the growth parameters through the Gompertz model, enabled a rapid and simultaneous exploration of the influence of pH, temperature and growth medium on both growth and bacteriocin production by vaginal Lact. salivarius CRL 1328.

Inhibition of growth of nonproteolytic Clostridium botulinum type B in sous vide cooked meat products is achieved by using thermal processing but not nisin

The safety of refrigerated processed foods of extended durability (REPFEDs) with respect to nonproteolytic Clostridium botulinum is under continuous evaluation. In the present study, mild (P7.0(85.0) values 0 to 2 min [P, pasteurization value; z-value 7.0 degrees C; reference temperature 85.0 degrees C]) and increased (P7.0(85.0) values 67 to 515 min) heat treatments were evaluated in relation to survival of nonproteolytic C. botulinum type B spores in sous vide processed ground beef and pork cubes. The use of two concentrations of nisin in inhibition of growth and toxin production by nonproteolytic C. botulinum in the same products was also evaluated. A total of 96 samples were heat processed and analyzed for C. botulinum by BoNT/B gene-specific polmerase chain reaction and for botulinum toxin by a mouse bioassay after storage of 14 to 28 days at 4 and 8 degrees C. Predictably, after mild processing all samples of both products showed botulinal growth, and one ground beef sample became toxic at 8 degrees C. The increased heat processing, equivalent to 67 min at 85 degrees C. resulted in growth but not toxin production of C. botulinum in one ground beef sample in 21 days at 8 degrees C: in the pork cube samples no growth was detected. The increased heating of both products resulted in higher sensory quality than the milder heat treatment. Nisin did not inhibit the growth of nonproteolytic C. botulinum in either product; growth was detected in both products at 4 and 8 degrees C, and ground beef became toxic with all nisin levels within 21 to 28 days at 8 degrees C. Aerobic and lactic acid bacterial counts were reduced by the addition of nisin at 4 degrees C. The study demonstrates that the mild processing temperatures commonly employed in sous vide technology do not eliminate nonproteolytic C. botulinum type B spores. The intensity of each heat treatment needs to be carefully evaluated individually for each product to ensure product safety in relation to nonproteolytic C. botulinum.

Bacteria associated with processed crawfish and potential toxin production by Clostridium botulinum type E in vacuum-packaged and aerobically packaged crawfish tails

Refrigerated vacuum-packaged storage has been shown to increase significantly the shelf life of fresh fish and seafood products, but the effect, if any, on the outgrowth and toxin production of Clostridium botulinum type E on cooked crawfish is unknown. Microflora associated with live crawfish reflect the microbial populations of the harvest water and sediments in which they are living. The presence or absence of specific pathogens in either vacuum-packaged or air-permeable bags of cooked crawfish have not been thoroughly evaluated. This study evaluates the potential survival and outgrowth of biological hazards in both vacuum-packaged and air-permeable-packaged cooked crawfish held at 4 and 10 degrees C for 30 days. During shelf-life studies of vacuum-packaged and air-permeable-bagged cooked crawfish, a total of 31 bacterial species were isolated and identified from crawfish samples using both selective and nonselective media. The only pathogens isolated from both vacuum-packed and air-permeable bags of processed crawfish samples during shelf-life studies were strains of Aeromonas hydrophila and Staphylococcus aureus. C. botulinum type E and Clostridium perfringens species were not isolated from any of the uninoculated crawfish samples. Cooked crawfish were inoculated with 10(3) C. botulinum type E spores per g of crawfish tail meat to determine whether cooked crawfish tails would support the growth of C. botulinum type E strains and produce toxin at refrigerated temperatures. Spore-inoculated crawfish tails were vacuum packaged in both a high barrier film and an air-permeable bag and stored at 4 degrees C and 10 degrees C for 30 days. C. botulinum toxin E was not detected in any of the spore-inoculated packages throughout the shelf-life study until day 30. Microbiological data from this study should be useful in the development and implementation of the hazard analysis and critical control point plans for processed crawfish tails.

Characterization of a bacteriocin-like substance produced by a vaginal Lactobacillus salivarius strain

A novel bacteriocin-like substance produced by vaginal Lactobacillus salivarius subsp. salivarius CRL 1328 with activity against Enterococcus faecalis, Enterococcus faecium, and Neisseria gonorrhoeae was characterized. The highest level of production of this heat-resistant peptide or protein occurred during the late exponential phase. Its mode of action was shown to be bactericidal. L. salivarius subsp. salivarius CRL 1328 could be used for the design of a probiotic to prevent urogenital infections.

Characterization of fatty acid composition, spore germination, and thermal resistance in a nisin-resistant mutant of Clostridium botulinum 169B and in the wild-type strain

The membrane fatty acids, thermal resistance, and germination of a nisin-resistant (Nisr) mutant of Clostridium botulinum 169B were compared with those of the wild-type (WT) strain. In the membranes of WT cells, almost 50% of the total fatty acids were unsaturated, but in those of Nisr cells, only 23% of the fatty acids were unsaturated. WT and Nisr spores contained similar amounts (approximately 23%) of unsaturated fatty acids, but the saturated straight-chain/branched-chain ratio was significantly higher in Nisr spores than in WT spores. These fatty acid differences suggest that Nisr cell and spore membranes may be more rigid, a characteristic which would interfere with the pore-forming ability of nisin. Nisr C. botulinum did not produce an extracellular nisin-degrading enzyme, nor were there any differences in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of coat proteins extracted from WT and Nisr spores, eliminating these as possible reasons for nisin resistance. Nisr spores had thermal resistance parameters similar to those of WT spores. In WT spores, but not in Nisr spores, nisin caused a 40% reduction in thermal resistance and a twofold increase in the germination rate. Because the nisin-induced increase in the germination rate of WT spores occurred only in the presence of a germinant (a molecule that triggers germination), nisin can be classified as a progerminant (a molecule that stimulates germination only in the presence of a germinant).

Inhibition of Bacillus licheniformis spore growth in milk by nisin, monolaurin, and pH combinations

The effects of nisin and monolaurin, alone and in combination, were investigated on Bacillus licheniformis spores in milk at 37 degrees C. In the absence of inhibitors, germinated spores developed into growing vegetative cells and started sporulation at the end of the exponential phase. In the presence of nisin (25 IU ml-1), spore outgrowth was inhibited (4 log10 reduction at 10 h). Regrowth appeared between 10 and 24 h and reached a high population level (1.25 x 10(8) cfu ml-1) after 7 d. Monolaurin (250 micrograms ml-1) had a bacteriostatic effect during the first 10 h but thereafter, regrowth occurred slowly with a population level after 7 d (4 x 10(5) cfu ml-1) lower than that of nisin. Different combined effects of nisin (between 0 and 42 IU ml-1), monolaurin (ranging from 0 to 300 micrograms ml-1), pH values (between 5.0 and 7.0) and spore loads (10(3), 10(4), 10(5) spores ml-1) were investigated using a Doehlert matrix in order to study the main effects of these factors and the different interactions. Results were analysed using the Response Surface Methodology (RSM) and indicated that nisin and monolaurin had no action on spores before germination; only pH values had a significant effect (P < or = 0.001), i.e. spore count decreased as the pH value increased in relation to germination. Sublethal concentrations of nisin (30 IU ml-1) and monolaurin (100 micrograms ml-1) in combination acted synergistically on outgrown spores and vegetative cells, showing total inhibition at pH 6.0, without regrowth, within 7 d at 37 degrees C.

Sodium nitrite and potassium nitrate in control of nonproteolytic Clostridium botulinum outgrowth and toxigenesis in vacuum-packed cold-smoked rainbow trout

The effect of sodium-nitrite (NaNO2) and potassium nitrate (KNO3) on the outgrowth and toxigenesis of nonproteolytic Clostridium botulinum in vacuum-packed cold-smoked rainbow trout stored for-six weeks was studied in two inoculation studies at slightly abusive storage temperatures of 4 degrees C and 8 degrees C. The depletion rate of nitrite and the reduction rate of nitrate to nitrite as well as the effect of nitrite and nitrate on the shelf-life of the product during eight weeks' storage period were also determined. The nitrite concentrations were reduced from 166 mg/kg +/- 9 (mean +/- SE), to a final concentration of 34 mg/kg +/- 2 and 11 mg/kg +/- 2, and the nitrate concentrations from 686 mg/kg +/- 67 to 465 mg/kg +/- 140 and 427 mg/kg +/- 33 at 4 degrees C and 8 degrees C respectively. The nitrite depletion rate was more rapid at 8 degrees C; nitrate depletion was not significantly affected by temperature. A considerable amount of nitrite was detected in the nitrate-treated samples in the latter half of the storage period. At 4 degrees C the aerobic plate counts were significantly lower in the samples treated with NaNO2 + NaCl and with KNO3 + NaCl as compared to the NaCl-treated controls, while at 8 degrees C the differences were smaller. The sensorial shelf-life of the product was considerably extended by nitrite and nitrate curing. The nitrite and nitrate concentrations used in the present study did not completely inhibit the toxigenesis of nonproteolytic C. botulinum during the six-week storage period, although the number of toxic samples was considerably reduced by nitrite and nitrate curing.

Production of nisin-like bacteriocins by Lactococcus lactis strains isolated from vegetables

Four bacteriocin producing lactic acid bacteria isolated from vegetables were identified as Lactococcus lactis strains on the basis of physiological and biochemical characteristics, carbohydrate fermentation patterns and analysis of total soluble protein pattern by SDS PAGE. The bacteriocins had a wide spectrum of activity as antagonism was detected not only towards a variety of lactic acid bacteria, but also to Staphylococcus aureus and Listeria monocytogenes. These bacteriocins were resistant to heating at 121 degree C for 15 minutes and showed highest activity at low pH (<5.0). They were inactivated by the proteolytic enzymes alpha-chymotrypsin and proteinase K, but not by lipase, alpha-amylase, catalase or lysozyme. These bacteriocinogenic Lactococcus strains were all immune to the bacteriocins produced as well as to commercial nisin. Bacteriocin producer culture supernatants showed a high degree (70 or 100%) of cross-reactivity in the nisin ELISA, suggesting similarity of the produced bacteriocins to nisin. The potential application of bacteriocin producing lactococci of vegetable origin for safety assurance of vegetable foods and controlling vegetable fermentations is discussed.

Biopreservation by lactic acid bacteria

Biopreservation refers to extended storage life and enhanced safety of foods using the natural microflora and (or) their antibacterial products. Lactic acid bacteria have a major potential for use in biopreservation because they are safe to consume and during storage they naturally dominate the microflora of many foods. In milk, brined vegetables, many cereal products and meats with added carbohydrate, the growth of lactic acid bacteria produces a new food product. In raw meats and fish that are chill stored under vacuum or in an environment with elevated carbon dioxide concentration, the lactic acid bacteria become the dominant population and preserve the meat with a "hidden' fermentation. The same applies to processed meats provided that the lactic acid bacteria survive the heat treatment or they are inoculated onto the product after heat treatment. This paper reviews the current status and potential for controlled biopreservation of foods.

Application of antimicrobial-producing lactic acid bacteria to control pathogens in ready-to-use vegetables

Five psychrotrophic strains of lactic acid bacteria (Lactobacillus casei, Lact. plantarum and Pediococcus spp.) were isolated from 22 samples of commercial salads. These strains were shown to inhibit Aeromonas hydrophila, Listeria monocytogenes, Salmonella typhimurium and Staphylococcus aureus on MRS agar, in salads and in juice prepared from vegetable salads. Lactobacillus casei IMPCLC34 was most effective in reducing total mesophilic bacteria and the coliform group; Aer. hydrophila, Salm. typhimurium and Staph. aureus disappeared after 6 d of storage, while the counts for L. monocytogenes remained constant. The potential application of antimicrobial-producing lactic acid bacteria as biopreservatives of ready-to-use vegetables is suggested.

Nisin stimulates oxygen consumption by Staphylococcus aureus and Escherichia coli

Nisin stimulated oxygen consumption by nongrowing, glucose-metabolizing Staphylococcus aureus and Escherichia coli cells, indicating a protonophore mode of action. A similar stimulation in E. coli cells osmotically stressed to disrupt the outer cell membrane confirmed the cytoplasmic membrane as the site of nisin action and showed that nisin uptake was not prevented by the outer membrane.

Production and characterization of enterocin 900, a bacteriocin produced by Enterococcus faecium BFE 900 from black olives

Enterococcus faecium BFE 900 isolated from black olives produced a bacteriocin termed enterocin 900, which was antagonistic towards Lactobacillus sake, Clostridium butyricum, enterococci as well as Listeria spp. including Listeria monocytogenes. Enterocin 900 was inactivated by pepsin, alpha-chymotrypsin, proteinase K and trypsin but not by catalase, alpha-amylase, or other non-proteolytic enzymes tested. The bacteriocin was heat stable, retaining activity after heating at 121 degrees C for 15 min. Enterocin 900 was active at pH values ranging from 2.0-10.0, with highest activity at pH 6.0. Bacteriocin production occurred in the late logarithmic growth phase when culture density was ca. log 8.0 CFU ml-1. Enterocin 900 was produced in media with initial pH ranging from 6.0-10.0, but not in media with a pH lower than 6.0. Medium composition, especially the concentrations of peptone and yeast extract influenced bacteriocin production, with no bacteriocin being produced in the absence of either of these compounds. No plasmids could be isolated from Enterococcus faecium BFE 900, indicating that the gene for bacteriocin activity is located on the chromosome.

Biological preservation of foods with reference to protective cultures, bacteriocins and food-grade enzymes

A review is presented on the present status of biological preservation of foods. Recent developments are discussed with respect to underlying mechanisms of inhibition by 'protective' cultures, and special reference is made to lactic acid bacteria (LAB) and their 'food-grade' safety. The role of bacteriocins, their limitations and potentiating role in biological systems, is also addressed. The use of enzymes (e.g. lysozyme) for food preservation is mainly restricted by economic factors, their inactivation by endogenous food components and their limited activity spectrum. Practical applications of protective cultures refer to particular food commodities that either constitute novel systems with respect to packaging and/or composition, or represent special hygienic risks. It is concluded that biological preservation cannot substitute GMP; it, however, offers an additional (and acceptable) processing parameter for improving the safety and assuring the quality of a given food.

Evidence that dissipation of proton motive force is a common mechanism of action for bacteriocins and other antimicrobial proteins

While bacteriocins from lactic acid bacteria (LAB) have generated tremendous interest among food microbiologists, they are not unique. The biosphere is awash with antimicrobial proteins such as colicins, defensins, cecropins, and magainins. These proteins share many characteristics. They are low molecular weight, cationic, amphiphilic, tend to aggregate and are benign to the producing organism. In cases where the mode of action has been investigated, the cell membrane appears to be the site of action. There is increasing evidence that bacteriocins from many bacterial genera also share these characteristics. After a brief introduction on the significance of LAB bacteriocins, this review provides some background on proton motive force. Current studies of mechanisms for various bacteriocins are reviewed. Evidence is then introduced that bacteriocins produced by lactic acid bacteria act by the common mechanism of depleting proton motive force. The role and importance of energized membranes in this process is examined. These observations are linked to literature which demonstrates that many other classes of antimicrobial proteins act by the same mechanism. Questions regarding the role of receptor proteins and the physical mechanism by which PMF is depleted remain unresolved.