Antibiosis revisited: bacteriocins produced by dairy starter cultures

Anaerobes as Sources of Bioactive Compounds and Health Promoting Tools

Aerobic microorganisms have been sources of medicinal agents for several decades and an impressive variety of drugs have been isolated from their cultures, studied and formulated to treat or prevent diseases. On the other hand, anaerobes, which are believed to be the oldest life forms on earth and evolved remarkably diverse physiological functions, have largely been neglected as sources of bioactive compounds. However, results obtained from the limited research done so far show that anaerobes are capable of producing a range of interesting bioactive compounds that can promote human health. In fact, some of these bioactive compounds are found to be novel in their structure and/or mode of action.Anaerobes play health-promoting roles through their bioactive products as well as application of whole cells. The bioactive compounds produced by these microorganisms include antimicrobial agents and substances such as immunomodulators and vitamins. Bacteriocins produced by anaerobes have been in use as preservatives for about 40 years. Because these substances are effective at low concentrations, encounter relatively less resistance from bacteria and are safe to use, there is a growing interest in these antimicrobial agents. Moreover, several antibiotics have been reported from the cultures of anaerobes. Closthioamide and andrimid produced by Clostridium cellulolyticum and Pantoea agglomerans, respectively, are examples of novel antibiotics of anaerobe origin. The discovery of such novel bioactive compounds is expected to encourage further studies which can potentially lead to tapping of the antibiotic production potential of this fascinating group of microorganisms.Anaerobes are widely used in preparation of fermented foods and beverages. During the fermentation processes, these organisms produce a number of bioactive compounds including anticancer, antihypertensive and antioxidant substances. The well-known health promoting effect of fermented food is mostly due to these bioactive compounds. In addition to their products, whole cell anaerobes have very interesting applications for enhancing the quality of life. Probiotic anaerobes have been on the market for many years and are receiving growing acceptance as health promoters. Gut anaerobes have been used to treat patients suffering from severe Clostridium difficile infection syndromes including diarrhoea and colitis which cannot be treated by other means. Whole cell anaerobes are also studied to detect and cure cancer. In recent years, evidence is emerging that anaerobes constituting the microbiome are linked to our overall health. A dysfunctional microbiome is believed to be the cause of many diseases including cancer, allergy, infection, obesity, diabetes and several other disorders. Maintaining normal microflora is believed to alleviate some of these serious health problems. Indeed, the use of probiotics and prebiotics which favourably change the number and composition of the gut microflora is known to render a health promoting effect. Our interaction with the microbiome anaerobes is complex. In fact, not only our lives but also our identities are more closely linked to the anaerobic microbial world than we may possibly imagine. We are just at the beginning of unravelling the secret of association between the microbiome and human body, and a clear understanding of the association may bring a paradigm shift in the way we diagnose and treat diseases and disorders. This chapter highlights some of the work done on bioactive compounds and whole cell applications of the anaerobes that foster human health and improve the quality of life.

Albusin B, mass-produced by the Saccharomyces cerevisiae suppression system, enhances lipid utilisation and antioxidant capacity in mice

BACKGROUND

Albusin B (bacteriocin), isolated from Ruminococcus albus 7 and mass-produced by the Saccharomyces cerevisiae expression system, has previously been shown to have a beneficial effect on lipid metabolism in broiler chickens. The present study was focused on the effect of albusin B on lipid metabolism in mice and the potential of albusin B-expressing yeast product (albusin B) as a food supplement. Forty-five BALB/c male mice at 6 weeks of age were each orally administered normal saline (control), yeast (0.125 mg kg(-1) ) or albusin B (0.125 mg kg(-1) ) for 14 days and then euthanised.

RESULTS

Compared with the control group, albusin B-fed mice exhibited decreased body weight and plasma levels of triglycerides and free fatty acids but increased plasma high-density lipoprotein. Albusin B-fed mice showed higher mRNA expression of fatty acid oxidation in the ileum, heart and liver than control mice. Compared with the control treatment, both yeast and albusin B treatments caused a decrease in mRNA expression of fatty acid synthesis in the heart and liver. Moreover, albusin B suppressed mRNA levels of lipogenesis in the ileum and liver. Albusin B-fed mice exhibited more favourable adenosine triphosphate production and antioxidant capacity in the heart and liver. Albusin B treatment led to a significantly lower respiratory quotient than that of the control, whereas yeast treatment did not.

CONCLUSION

This study demonstrated a beneficial effect of albusin B on lipid utilisation and anti-atherosclerotic and antioxidant capacities in mice. However, more comprehensive studies are required to elucidate the exact mechanism behind the effect of albusin B.

Production of organic acids by probiotic lactobacilli can be used to reduce pathogen load in poultry

Probiotic Lactobacillus can be used to reduce the colonization of pathogenic bacteria in food animals, and therefore reduce the risk of foodborne illness to consumers. As a model system, we examined the mechanism of protection conferred by Lactobacillus species to inhibit C. jejuni growth in vitro and reduce colonization in broiler chickens. Possible mechanisms for the reduction of pathogens by lactobacilli include: 1) stimulation of adaptive immunity; 2) alteration of the cecal microbiome; and, 3) production of inhibitory metabolites, such as organic acids. The Lactobacillus species produced lactic acid at concentrations sufficient to kill C. jejuni in vitro. We determined that lactic acid produced by Lactobacillus disrupted the membrane of C. jejuni, as judged by biophotonics. The spectral features obtained using Fourier-transform infrared (FT-IR) and Raman spectroscopy techniques were used to accurately predict bacterial viability and differentiate C. jejuni samples according to lactic acid treatment. FT-IR spectral features of C. jejuni and Lactobacillus grown in co-culture revealed that the metabolism was dominated by Lactobacillus prior to the killing of C. jejuni. Based on our results, the development of future competitive exclusion strategies should include the evaluation of organic acid production.

Production and characterization of a bacteriocin from ruminal bacterium Ruminococcus albus 7

The characteristics of a bacteriocin from Ruminococcus albus 7 and its potential as an antibiotic alternative were examined in this study. The addition of 3 µM 3-phenylpropanoic acid (PPA) and 0.2% Tween 80 to the culturing medium improved bacteriocin production by 2.5-fold. Native polyacrylamide gel electrophoresis of the antagonistically active gel filtration fraction established that the molecular weight of the R. albus 7 bacteriocin was approximately 36 kDa. The bacteriocin was sensitive to pepsin, protease, and pancreatin, and was inactivated by heating at 65 °C for 1 h. Simulating in vitro avian digestion decreased the antagonistic activity by 74.7%, but the addition of 1% bovin serum albumin restored 13% of the lost antagonistic activity. Following ion-exchange purification, the bacteriocin had sufficient antagonistic activity against five tested pathogenic strains, but the addition of a protectant is necessary for utilization of bacteriocin of R. albus 7 as an antibiotic alternative in animal feed.

Identification of the propionicin F bacteriocin immunity gene (pcfI) and development of a food-grade cloning system for Propionibacterium freudenreichii

This report describes the first functional analysis of a bacteriocin immunity gene from Propionibacterium freudenreichii and its use as a selection marker for food-grade cloning. Cloning of the pcfI gene (previously orf5 [located as part of the pcfABC propionicin F operon]) rendered the sensitive host 1,000-fold more tolerant to the propionicin F bacteriocin. The physiochemical properties of the 127-residue large PcfI protein resemble those of membrane-bound immunity proteins from bacteriocin systems found in lactic acid bacteria. The high level of immunity conferred by pcfI allowed its use as a selection marker for plasmid transformation in P. freudenreichii. Electroporation of P. freudenreichii IFO12426 by use of the pcfI expression plasmid pSL102 and propionicin F selection (200 bacteriocin units/ml) yielded 10(7) transformants/microg DNA. The 2.7-kb P. freudenreichii food-grade cloning vector pSL104 consists of the pLME108 replicon, a multiple cloning site, and pcfI expressed from the constitutive P(pampS) promoter for selection. The pSL104 vector efficiently facilitated cloning of the propionicin T1 bacteriocin in P. freudenreichii. High-level propionicin T1 production (640 BU/ml) was obtained with the IFO12426 strain, and the food-grade propionicin T1 expression plasmid pSL106 was maintained by approximately 91% of the cells over 25 generations in the absence of selection. To the best of our knowledge this is the first report of an efficient cloning system that facilitates the generation of food-grade recombinant P. freudenreichii strains.

Lactic acid bacteria isolated from canine faeces

AIMS

Lactic acid bacteria (LAB) were isolated and sequenced from the faeces of healthy dogs. Five of these strains were selected and further characterized to clarify the potential of these strains as probiotics for canine.

METHODS AND RESULTS

LAB were found in 67% (14/21) of the canine faeces samples when plated on Lactobacilli Selective Media without acetic acid. Out of 13 species identified with partial 16S rRNA gene sequencing, Lactobacillus fermentum LAB8, L. mucosae LAB12, L. rhamnosus LAB11, L. salivarius LAB9 and Weissella confusa LAB10 were selected as candidate probiotic strains based on their frequency, quantity in faeces, growth density, acid tolerance and antimicrobial activity. The minimal inhibitory concentration values of these isolates were determined for 14 antibiotics. L. salivarius LAB9, W. confusa LAB10 and L. mucosae LAB12 were viable in pH 2 for 4 h (mLBS), indicating tolerance to acidity and thus the potential to survive in gastrointestinal tract of the canine. The LAB8-LAB12 strains showed antimicrobial activity against Micrococcus luteus A1 NCIMB86166.

CONCLUSIONS

Thirteen different LAB species were found from the faecal microbiota of the healthy canines. Five acid tolerant and antimicrobially active LAB strains with the capacity to grow to high densities both aerobically and anaerobically were chosen to serve as candidate probiotics.

SIGNIFICANCE AND IMPACT OF THE STUDY

The selected LAB strains are among the first host-specific LAB with antimicrobial activity isolated from canines that could serve as potential probiotics for canine use.

Suppression of Helicobacter pylori-induced interleukin-8 production in vitro and within the gastric mucosa by a live Lactobacillus strain

BACKGROUND

Accumulating evidence indicates that interleukin-8 (IL-8) plays a major role in the mucosal inflammation caused by Helicobacter pylori infection. The purpose of the present study was to examine whether Lactobacillus gasseri OLL2716 (LG21) can inhibit the H. pylori-induced production of IL-8.

METHODS

A coculture system including MKN45 cells, H. pylori, and LG21 was established for an in vitro analysis. Biopsy specimens were obtained from H. pylori-infected human subjects consisting of 19 men and six women.

RESULTS

When LG21 was 1/100 less than H. pylori in a coculture system, LG21 significantly suppressed both the IL-8 mRNA and protein generation in the coculture. Live, but not heat- or UV-treated LG21, could exert the suppressive effect. However, this amount of LG21 could not suppress either the adhesion of H. pylori to the cell surface or the IL-8 production by tumor necrosis factor-alpha, which induces IL-8 generation through the activation of the transcription. These results thus suggest that LG21 suppresses an event leading to IL-8 production, which is specific for H. pylori-induced IL-8 generation, and this event is located upstream from the IL-8 transcription but downstream from the adhesion. The measurement of the IL-8 level using gastric biopsy specimens from H. pylori-infected subjects demonstrated that LG21 also suppresses the production of IL-8 in the gastric mucosa.

CONCLUSIONS

Live LG21 were found to suppress H. pylori-induced IL-8 production in both a gastric cell line and within gastric mucosa.

Streptococcus macedonicus ACA-DC 198 produces the lantibiotic, macedocin, at temperature and pH conditions that prevail during cheese manufacture

Streptococcus macedonicus ACA-DC 198, a natural cheese isolate, produces the anticlostridial bacteriocin, macedocin. Bacteriocin activity was detected from the mid-exponential growth phase and remained constant during the stationary phase. A secondary model was setup to describe the influence of temperature (20-45 degrees C) and pH (5.1-6.9) on cell growth of and bacteriocin production by S. macedonicus ACA-DC 198 during in vitro laboratory fermentations. The optimum temperature for bacteriocin production (20-25 degrees C) was markedly lower than the optimum growth temperature (42.3 degrees C). In contrast, the specific macedocin production was maximal around pH 6.0, whereas growth was optimal at pH 6.4. Consequently, the maximum bacteriocin activity was reached between pH 6.0 and 6.5.

Heterologous production of antimicrobial peptides in Propionibacterium freudenreichii

Heterologous bacteriocin production in Propionibacterium freudenreichii is described. We developed an efficient system for DNA shuttling between Escherichia coli and P. freudenreichii using vector pAMT1. It is based on the P. freudenreichii rolling-circle replicating plasmid pLME108 and carries the cml(A)/cmx(A) chloramphenicol resistance marker. Introduction of the propionicin T1 structural gene (pctA) into pAMT1 under the control of the constitutive promoter (P4) yielded bacteriocin in amounts equal to those of the wild-type producer Propionibacterium thoenii 419. The P. freudenreichii clone showed propionicin T1 activity in coculture, killing 90% of sensitive bacteria within 48 h. The pamA gene from P. thoenii 419 encoding the protease-activated antimicrobial peptide (PAMP) was cloned and expressed in P. freudenreichii, resulting in secretion of the pro-PAMP protein. Like in the wild type, PAMP activation was dependent on externally added protease. Secretion of the antimicrobial peptide was obtained from a clone in which the pamA signal peptide and PAMP were fused in frame. The promoter region of pamA was identified by fusion of putative promoter fragments to the coding sequence of the pctA gene. The P4 and Ppamp promoters directed constitutive gene expression, and activity of both promoters was enhanced by elements upstream of the promoter core region.

Reduction of Escherichia coli O157:H7 and Salmonella in ground beef using lactic acid bacteria and the impact on sensory properties

Studies were conducted to determine whether four strains of lactic acid bacteria (LAB) inhibited Escherichia coli O157: H7 and Salmonella in ground beef at 5 degrees C and whether these bacteria had an impact on the sensory properties of the beef. The LAB consisted of frozen concentrated cultures of four Lactobacillus strains, and a cocktail mixture of streptomycin-resistant E. coli O157:H7 and Salmonella were used as pathogens. Individual LAB isolates at 10(7) CFU/ml were added to tryptic soy broth containing a pathogen concentration of 10(5) CFU/ml. Samples were stored at 5 degrees C, and pathogen populations were determined on days 0, 4, 8, and 12. After 4 days of storage, there were significant differences in numbers of both pathogens exposed to LAB isolates NP 35 and NP 3. After 8 and 12 days of storage, all LAB reduced populations of both pathogens by an average of 3 to 5 log cycles. A second study was conducted in vacuum-packaged fresh ground beef. The individual LAB isolates resulted in an average difference of 1.5 log cycles of E. coli O157:H7 after 12 days of storage, and Salmonella populations were reduced by an average of 3 log cycles. Following this study, a mixed concentrated culture was prepared from all four LAB and added to ground beef inoculated with pathogen at 10(8) CFU/g. After 3 days of storage, the mixed culture resulted in a 2.0-log reduction in E. coli O157:H7 compared with the control, whereas after 5 days of storage, a 3-log reduction was noted. Salmonella was reduced to nondetectable levels after day 5. Sensory studies on noninoculated samples that contained LAB indicated that there were no adverse effects of LAB on the sensory properties of the ground beef. This study indicates that adding LAB to raw ground beef stored at refrigeration temperatures may be an important intervention for controlling foodborne pathogens.

Isolation of Bacillus circulans and Paenibacillus polymyxa strains inhibitory to Campylobacter jejuni and characterization of associated bacteriocins

We evaluated anti-Campylobacter activity among 365 Bacillus and Paenibacillus isolates from poultry production environments. One novel antagonistic Bacillus circulans and three Paenibacillus polymyxa strains were identified and further studied. Cell-free ammonium sulfate precipitate (crude antimicrobial preparation) was obtained from each candidate culture. Zones of Campylobacter growth inhibition surrounding 10 microl of this crude antimicrobial preparation were quantified using a spot test. Campylobacter growth resumed when the preparation was preincubated with selected protease enzymes, demonstrating peptide characteristics consistent with a bacteriocin. These peptides were further purified using combinations of molecular mass resolution and ion exchange chromatography. Molecular masses of the peptides were estimated at approximately 3,500 Da by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Isoelectric focusing was used to determine the pI values of the peptides. Amino acid sequences of the bacteriocins and more precise molecular masses were obtained by matrix-assisted laser desorption and ionization-time of flight (MALDI-TOF) analysis. The bacteriocin from P. polymyxa NRRL B-30507 had a pI of 4.8, that from P. polymyxa NRRL B-30509 had a pI of 7.2, that from P. polymyxa NRRL B-30508 had a pI of 4.8, and that from B. circulans NRRL B-30644 had a pI of 7.8. The amino acid sequences were consistent with those of class IIa bacteriocins. These antagonists and the corresponding bacteriocins may be useful in the control of Campylobacter infection in poultry.

In vitro growth inhibition of major mastitis pathogens by Staphylococcus chromogenes originating from teat apices of dairy heifers

Earlier field observations suggest that teat apex colonization by Staphylococcus chromogenes pre-partum in dairy heifers protects udder quarters against elevated somatic cell counts early post-partum. To explain these findings, the in vitro inhibitory capability of S. chromogenes from teat apices of heifers towards some major mastitis pathogens was tested using a modified cross-streaking method. Two out of 10 S. chromogenes isolates, both originating from two different teats from the same heifer, consistently inhibited growth of all Staphylococcus aureus, Streptococcus dysgalactiae, and Streptococcus uberis strains, but none of the Escherichia coli strains. The present study, therefore, supports the protective effect of teat apex colonization by S. chromogenes by in vitro production of inhibitory substances.

Food-grade chemical and biological agents permeabilize red beet hairy roots, assisting the release of betalaines

Hairy root cultures of red beet, Beta vulgaris L., were permeabilized under the functions of food-grade chemical and biological agents cetyl trimethylammonium bromide (CTAB), Triton X-100, Tween-80, Lactobacillus helveticus, Saccharomyces cereviseae, and Candida utilis, as well as cell fractions of L. helveticus, for the recovery of betalaines with or without oxygen stress. Tween-80 (0.15%), Triton X-100 (0.2%), and CTAB (0.05%), in combination with oxygen stress, released 45%, 70%, and 90% pigment into the medium, respectively, with significantly lesser levels in agitated cultures receiving similar treatments. The release was rapid (1 h) in CTAB treatment with a much slower release in Tween-80. CTAB (0.002%) was found to be also useful in effluxing betalaines (80%) from hairy roots grown in a bubble column reactor. Viability of permeabilized hairy roots, tested on agar medium, was not affected by any level of CTAB treatment and was significantly retarded at higher levels of Triton X-100 and Tween-80. An altogether new approach of pigment release using biological agents such as live cells of food-grade microbes was used where C. utilis, L. helveticus, and S. cereviseae released 60%, 85%, and 54% betalaines, respectively, in 24 h, though lower level treatments also released similar levels of pigment by 48 h. Dried whole cell powder of L. helveticus, its total insoluble carbohydrate, and free lipid fractions released 10%, 0%, and 85% pigment, respectively. An extended study with a bubble column reactor using the free lipid fraction of L. helveticus showed 50% and 84% pigment release in 8 and 12 h, respectively, exhibiting good viability when plated on agar medium. Even in the bioreactor, replenishment of medium 8 h after treatment with free lipid of L. helveticus allowed regrowth of hairy roots. The high level of pigment release recorded here, using CTAB or lipid of L. helveticus, appears useful for developing processes for in situ recovery of betalaines. The live microbes, applicable only for batch cultures, are expected to impart improved sensory/nutraceutical effects to the recovered pigment and hence may add value to the product receiving the red beet pigment thus produced.

Effect of enterococcin A 2000 on biological and synthetic phospholipid membranes

Lactic acid bacterium isolated from Bulgarian cheese and identified as Enterococcus faecium produces a small hydrophobic peptide substance (enterococcin A 2000) with broad spectrum of antimicrobial activity. The wide range of enterococcin antibacterial activity of this compound against Gram-positive, as well as against some Gram-negative bacteria, suggests a single mechanism of action. The mode of action of enterococcin A 2000 was studied in intact liver mitochondria and synthetic phospholipid liposomes used as model systems. Enterococcin A 2000 stimulated the ATPase activity in intact mitochondria. The kinetic curve of ATP hydrolysis differed from that obtained in presence of dinitrophenol (DNP) and showed a character similar to the ATP hydrolysis in the presence of classic ionophores. Enterococcin A 2000, when bound to synthetic phospholipid liposomes, permeabilized liposomes liberating the marker carboxyfluorescein (CF).

Effects of bacterial direct-fed microbials on ruminal fermentation, blood variables, and the microbial populations of feedlot cattle

A study was conducted to determine whether bacterial direct-fed microbials (DFM) could be used to minimize the risk of acidosis in feedlot cattle receiving high concentrate diets. Six ruminally cannulated steers, previously adapted to a high concentrate diet, were used in a double 3 x 3 Latin square to study the effects of DFM on feed intake, ruminal pH, and ruminal and blood characteristics. Steers were provided ad libitum access to a diet containing steam-rolled barley, barley silage, and a protein-mineral supplement at 87, 9, and 4% (DM basis), respectively. Treatments were as follows: control, Propionibacterium P15 (P15), and Propionibacterium P15 and Enterococcus faecium EF212 (PE). The bacterial treatments (10(9) cfu/g) plus whey powder carrier, or whey powder alone for control, were top-dressed once daily at the time of feeding (10 g/[steer/d]). Periods consisted of 2 wk of adaptation and 1 wk of measurements. Ruminal pH was continuously measured for 6 d using indwelling electrodes. Dry matter intake and ruminal pH (mean, minimum, hours, and area pH < 5.8 or < 5.5) were not affected by treatment (P > 0.05). However, supplementation with P15 increased protozoal numbers (P < 0.05) with a concomitant increase in ruminal NH3 concentration (P < 0.01) and a decrease in the number of amylolytic bacteria (P < 0.05) compared with the control. Streptococcus bovis, enumerated using a selective medium, was numerically reduced with supplementation of PE. Although blood pH and blood glucose were not affected by DFM supplementation, steers fed PE had numerically lower concentrations of blood CO2 than control steers, which is consistent with a reduced risk of metabolic acidosis. Although the bacterial DFM used in this study did not induce changes in DMI or ruminal and blood pH, some rumen and blood variables indicated that the bacterial DFM used in this study may decrease the risk of acidosis in feedlot cattle.

Competitive inhibition of Listeria monocytogenes in ready-to-eat meat products by lactic acid bacteria

Forty-nine strains of lactic acid bacteria (LAB), isolated from commercially available ready-to-eat (RTE) meat products, were screened for their ability to inhibit the growth of Listeria monocytogenes at refrigeration (5 degrees C) temperatures on agar spot tests. The three most inhibitory strains were identified as Pediococcus acidilactici, Lactobacillus casei, and Lactobacillus paracasei by 16S rDNA sequence analysis. Their antilisterial activity was quantified in associative cultures in deMan Rogosa Sharpe (MRS) broth at 5 degrees C for 28 days, resulting in a pathogen reduction of 3.5 log10 cycles compared to its initial level. A combined culture of these strains was added to frankfurters and cooked ham coinoculated with L. monocytogenes, vacuum packaged, and stored at 5 degrees C for 28 days. Bacteriostatic activity was observed in cooked ham, whereas bactericidal activity was observed in frankfurters. Numbers of L. monocytogenes were 4.2 to 4.7 log10 and 2.6 log10 cycles lower than controls in frankfurters and cooked ham, respectively, after the 28-day refrigerated storage. In all cases, numbers of LAB increased by only 1 log10 cycle. The strain identified as P. acidilactici was possibly a bacteriocin producer, whereas the antilisterial activity of the other two strains was due to the production of organic acids. There was no significant difference (P > 0.05) in the antilisterial activity detected in frankfurters whether the LAB strains were used individually or as combined cultures. Further studies over a 56-day period indicated no impact on the quality of the product. This method represents a potential antilisterial intervention in RTE meats, because it inhibited the growth of the pathogen at refrigeration temperatures without causing sensory changes.

A rapid procedure for isolating chromosomal DNA from Lactobacillus species and other Gram-positive bacteria

This study describes a rapid procedure for the isolation of genomic DNA from various Gram-positive bacteria. Species tested included Lactobacillus delbrueckii subsp. lactis ATCC 4797, Lact. acidophilus N2, Staphylococcus aureus, Staph. epidermidis, Propionibacterium jensenii P126, Bacillus pumilus and Enterococcus faecalis. Our technique for chromosomal DNA isolation circumvents the need for phenol-chloroform extractions and caesium chloride gradients. Isolated DNA is consistently greater than 25 kb in size and can be used directly for subcloning, polymerase chain reaction amplification, restriction digestions and library construction.

Behavior of Listeria monocytogenes in pasteurized milk during fermentation with lactic acid bacteria

The behavior of Listeria monocytogenes in pasteurized milk during fermentation with starter and nonstarter lactic acid bacteria was investigated. Pasteurized milk was co-inoculated with approximately 10(4) CFU/ml of L. monocytogenes and 10(6) CFU/ml of Lactococcus lactis, Lactococcus cremoris, Lactobacillus plantarum, Lactobacillus bulgaricus, or Streptococcus thermophilus. Inoculated milks were incubated at 30 degrees C or 37 degrees C for 24 to 72 h. Listeria monocytogenes survived and also grew to some extent during incubation in the presence of all starter cultures; however, inhibition ranged from 83 to 100% based on maximum cell populations. During incubation with L. bulgaricus and L. plantarum, L. monocytogenes was completely inactivated after 20 h and 64 h of incubation at 37 degrees C and 30 degrees C, respectively. The pH of the fermenting milks declined steadily throughout the fermentation periods and was approximately 4.2 at the conclusion of the experimental period regardless both of the starter culture and pathogen combination or the temperature of incubation.

Isolation, partial purification and characterization of a bacteriocin produced by a newly isolated Bacillus subtilis strain

A wild type micro-organism producing antibacterial substances has been isolated from a Chinese fermented soybean seasoning and identified as Bacillus subtilis. A crude antibacterial preparation (CABP) was obtained by ammonium sulphate precipitation. Isoelectric focusing assay revealed at least four antimicrobial components in the CABP. However, in SDS-PAGE analysis, only one peptide band displayed antimicrobial activity against pathogenic Bacillus cereus and Listeria monocytogenes. This inhibitory peptide had a molecular weight of approximately 3.4 kDa and a pI value of approximately 4.7. Results of this study suggest that at least one antimicrobial substance produced by this wild type strain of B. subtilis may be a new bacteriocin. Its sensitivity to gastric peptidases and activity against the food-borne pathogens make this bacteriocin potentially useful as an antimicrobial agent in foods.

Isolation and characterization of a bacteriocin (Butyrivibriocin AR10) from the ruminal anaerobe Butyrivibrio fibrisolvens AR10: evidence in support of the widespread occurrence of bacteriocin-like activity among ruminal isolates of B. fibrisolvens

Forty-nine isolates of Butyrivibrio fibrisolvens and a single isolate of Butyrivibrio crossotus were screened for the production of inhibitors by a deferred plating procedure. Twenty-five isolates produced factors which, to various degrees, inhibited the growth of the other Butyrivibrio isolates. None of the inhibitory activity was due to bacteriophages. The inhibitory products from 18 of the producing strains were sensitive to protease digestion. Differences in the ranges of activity among the Butyrivibrio isolates and protease sensitivity profiles suggest that a number of different inhibitory compounds are produced. These findings suggest that the production of bacteriocin-like inhibitors may be a widespread characteristic throughout the genus Butyrivibrio. The bacteriocin-like activity from one isolate, B. fibrisolvens AR10, was purified and confirmed to reside in a single peptide. Crude bacteriocin extracts were prepared by ammonium sulfate and methanol precipitation of spent culture supernatants, followed by dialysis and high-speed centrifugation. The active component was isolated from the semicrude extract by reverse-phase chromatography. Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis confirmed that the peptide was purified to homogeneity, having an estimated molecular mass of approximately 4,000 Da. The N terminus of the peptide was blocked. A cyanogen bromide cleavage fragment of the native peptide yielded a sequence of 20 amino acids [(M)GIQLAPAXYQDIVNXVAAG]. No homology with previously reported bacteriocins was found. Butyrivibriocin AR10 represents the first bacteriocin isolated from a ruminal anaerobe.

Are ruminal bacteria armed with bacteriocins?

The production of toxic compounds or antibiotics is a common component of intermicrobial competitive interactions, and many of these toxins have been adopted and adapted for the control of microbial populations. One class of these toxins, the bacteriocins, is a heterogeneous group of proteinaceous antibiotics that often display a high degree of target specificity, although many have a very wide spectrum of activity. To date, only limited information is available concerning the occurrence of bacteriocins among ruminal isolates or the sensitivity of ruminal microorganisms to exogenous bacteriocins. A survey of 50 strains of Butyrivibrio spp. isolated from a variety of sources (sheep, deer, and cattle) for bacteriocin production indicated a high incidence of bacteriocin-like activity (50%). Many of these inhibitory compounds appear to have a broad spectrum of activity, which suggests that bacteriocins may have a significant impact on both the competitive fitness of individual microbial strains within the rumen and on the overall structure of the microbial population within the rumen. Selected bacteriocins from lactic acid bacteria also were shown to have activity against Butyrivibrio spp. and may have application in ruminant systems. Bacteriocins may provide an alternative group of antibiotics for the manipulation of ruminal microbial populations. Bacteriocins have significant advantages over other antibiotics in target specificity, susceptibility to proteolytic digestion, possibility of genetic transfer and manipulation, and, in the case of some bacteriocins derived from lactic acid bacteria, a long history of safe use.