Antibacterial polypeptides of Lactobacillus species

Characterization of diacetin B, a bacteriocin from Lactococcus lactis subsp. lactis bv. diacetylactis UL720

Fourteen Lactococcus lactis strains showing inhibitory activity against Listeria innocua SICC 4202 were isolated from different French raw milks and raw milk cheeses and screened for bacteriocin production by the triple layer method under conditions that eliminate the effects of lactic acid and hydrogen peroxide. Three bacteriocinogenic strains (two Lactococcus lactis subsp. lactis bv. diacetylactis UL719 and UL720 and one Lactococcus lactis subsp. lactis UL730) were selected for their high capacity to inhibit the growth of various food pathogens, including Listeria monocytogenes, Staphylococcus aureus, and clostridial strains. The inhibitory compounds from these three strains are inactivated by selected proteases, indicating their protein nature. They retained their antibacterial activity after heat treatments of 100 degrees C for 60 min and 121 degrees C for 20 min, and in the pH range from 2 to 11. The bacteriocin diacetin B produced by strain UL720 has been purified by a pH-dependent adsorption-desorption procedure, followed by reverse-phase high performance liquid chromatography, with a yield of 1.25% of the original activity. Mass spectrometry analysis indicates that the pure peptide has a molecular mass of 4292.32 or 4490.28 Da, while amino acid sequencing allowed the identification of the primary structure of the bacteriocin composed of 37 amino acid residues. The structure of the peptide did not show similarity with other known bacteriocins from lactic acid bacteria.

In vitro fructooligosaccharide utilization and inhibition of Salmonella spp. by selected bacteria

In vitro experiments were conducted to determine: 1) inhibitory capacities of potential direct-fed microbial bacteria against Salmonella serotypes; and 2) the ability of Bifidobacterium bifidum, Enterococcus faecium, Lactobacillus casei, Lactococcus lactis, Pediococcus sp., and Salmonella spp. to grow in media containing fructooligosaccharides (FOS-50 or FOS pure formulation) as the only carbohydrate source. Thirteen bacteria (two strains of Bacillus coagulans, Bacillus licheniformis, Bacillus subtilis, B. bifidum, E. faecium, two strains of Lactobacillus acidophilus, L. casei, Pediococcus sp., Propionibacterium acidopropionici, P. jensenii, and Propionibacterium sp.) were tested for inhibition of six Salmonella serotypes (S. california, S. enteritidis, S. heidelberg, S. mission, S. senftenberg, and S. typhimurium) using a spot-the-lawn technique. Bifidobacterium bifidum, E. faecium, all lactobacilli, and Pediococcus sp. clearly inhibited growth of all Salmonella serotypes. In the growth experiments, E. faecium, L. lactis, and Pediococcus sp. grew in media with either FOS-50 or the pure formulation of FOS as the sole carbohydrate source. All tested Salmonella serotypes utilized FOS-50 for growth; however growth varied among the serotypes. In contrast, none of the Salmonella serotypes grew in media containing the pure formulation of FOS as the only carbohydrate source.

Immobilized cells in meat fermentation

The immobilization of microbial cells can contribute to fermented meat technology at two basic levels. First, the solid/semisolid nature (low available water) of the substrate restricts the mobility of cells and results in spatial organizations based on "natural immobilization" within the fermentation matrix. The microniches formed influence the fermentation biochemistry through mass transfer limitations and the subsequent development and activity of the microflora. This form of immobilization controls the nature of competition between subpopulations within the microflora and ultimately exerts an effect on the ecological competence (ability to survive and compete) of the various cultures present. Second, immobilized cell technology (ICT) can be used to enhance the ecological competence of starter cultures added to initiate the fermentation. Immobilization matrices such as alginate can provide microniches or microenvironments that protect the culture during freezing or lyophilization, during subsequent rehydration, and when in competition with indigenous microflora. The regulated release of cells from the microenvironments can also contribute to competitive ability. The regulation of both immobilization processes can result in enhanced fermentation activity.

Antibacterial activity of three Leuconostoc strains isolated from vacuum-packaged processed meats

One hundred and fifty lactic acid bacteria (LAB) isolated from vacuum-packaged processed meats were screened for antagonistic activity against various food spoilage microorganisms and foodborne pathogens. Nineteen strains produced bacteriocins active against closely related LAB and Listeria strains. Leuconostoc carnosum (LA54a and TA26b) and Leuconostoc mesenteroides subspecies dextranicum (TA33a) produced bacteriocins that were susceptible to proteolytic enzymes, but not to catalase, lysozyme or chloroform. They were heat stable up to 100 degrees C for thirty minutes at pH 2 to 7, and exerted a bacteriolytic effect. Bacteriocin production by all Leuconostoc strains was growth associated, occurring at incubation temperatures of 0 degrees C to 30 degrees C and initial medium pH 4.5 to 7.5. Probing of plasmid DNA from the three Leuconostoc strains with an oligonucleotide probe homologous to the nucleotide sequence of leucocin A-UAL 187 indicated plasmid-mediated bacteriocin production. Homology of the three Leuconostoc bacteriocin-coding genes to the amino-terminal end of the leucocin A-UAL 187 gene from Leuconostoc gelidum UAL 187 is therefore suggested. This evidence implies that all three Leuconostoc strains produce type 2, Listeria active bacteriocins.

Caseicin, a bacteriocin from Lactobacillus casei

The intracellular bacteriocin caseicin 80 was purified from cell extracts of Lactobacillus casei strain B80. It is a thermolabile protein with an apparent molar mass of 42 kDa. As no plasmids were observed in the bacteriocinogenic strain it is assumed that caseicin is encoded by the bacterial chromosome. Using 14C-labelled precursors it was found that biosynthesis of DNA and proteins was influenced by caseicin but this inhibition is probably not the primary effect. The incorporation of fructose but not of glucose into cellular material was inhibited by caseicin.

Bacteriocin production by Carnobacterium piscicola LV 61

Carnobacterium piscicola LV 61 produces a bacteriocin designated piscicolin 61, that is heat resistant, active over a wide pH range and inactivated by alpha-chymotrypsin, pepsin, trypsin and papain. It is effective against strains of the genera Carnobacterium, Enterococcus and Listeria. Other lactic acid bacteria tested were less sensitive or resistant to piscicolin. It is produced at temperatures from 1 to 30 degrees C. Maximum bacteriocin activity was detected after the culture had entered the stationary phase of growth and when the culture was grown in a medium with an initial pH between 8.0 and 9.0. The same high amounts of bacteriocin could be obtained in a culture at a constant pH of 6.5. No bacteriocin was produced at pH 5.0. Peptone in the growth medium promotes bacteriocin production, whereas meat and yeast extract did not influence the amounts of bacteriocin produced. Bacteriocin production and immunity are probably encoded by a 22 kb plasmid.

Antimicrobial activity of lactic acid bacteria isolated from sour doughs: purification and characterization of bavaricin A, a bacteriocin produced by Lactobacillus bavaricus MI401

Three hundred and thirty-five lactic acid bacteria were isolated from sour doughs and screened for antagonistic activity. Of these 145 showed activity against one or several of the indicator strains used in the screening. The antimicrobial activity of 18 isolates were due to a proteinaceous compound. These 18 isolates belonged to three different Lactobacillus species: Lactobacillus bavaricus, Lactobacillus curvatus and Lactobacillus plantarum. The spectrum of antimicrobial activity for the three species suggested that the inhibitory components were different. The inhibitory compound from Lact. bavaricus MI401 was chosen for further study. The proteinaceous nature, antimicrobial activity against closely-related species, heat resistance and sensitivity to alkaline treatment strongly indicated that this substance was a bacteriocin, which we designated bavaricin A. The bacteriocin was purified to homogeneity by ammonium sulphate precipitation, ion exchange, hydrophobic interaction and reverse-phase chromatography. The purification resulted in 193,000-fold increase in specific activity. SDS-PAGE of bavaricin A showed a molecular weight of 3500-4000 Da. By amino acid sequencing 41 amino acids were determined. Bavaricin A had a bactericidal mode of action and inhibited nine out of 10 Listeria monocytogenes. Lactobacillus bavaricus MI401 produced bavaricin A at temperatures from 4 degrees C to 30 degrees C. The production of active bavaracin A was inhibited at increasing sodium chloride concentration. In the presence of 3% sodium chloride at 4 degrees C no active bavaricin A could be detected. Nitrite (100 ppm) did not affect the production of active bavaricin A.

Antibiosis revisited: bacteriocins produced by dairy starter cultures

Well before the existence of starter bacteria was recognized, their activities were instrumental in preserving dairy foods. During growth in fermented products, dairy starters, including lactobacilli, lactococci, leuconostocs, streptococci, and propionibacteria, produce inhibitory metabolites. Inhibitors include broad-spectrum antagonists, organic acids, diacetyl, and hydrogen peroxide. Some starters also produce bacteriocins or bactericidal proteins active against species that usually are related closely to the producer culture. Several bacteriocins have been biochemically and genetically characterized. Evaluating properties of the Lactobacillus acidophilus bacteriocin, lactacin B, led to a new purification protocol. Purified lactacin B migrates in SDS-PAGE as a single 8100-Da band with inhibitory activity after Coomassie blue staining. Production of lactacin B is enhanced by cultivation of the producer with the sensitive indicator, Lactobacillus delbrueckii ssp. lactis 4797; understanding this interaction may increase knowledge of production of bacteriocins in heterogeneous cultures. Bacteriocins have been recently identified in dairy propionibacteria. Jenseniin G, a bacteriocin produced by Propionibacterium jensenii P126, has narrow activity; propionicin PLG-1 produced by Propionibacterium thoenii P127 inhibits propionibacteria, some fungi, Campylobacter jejuni, and additional pathogens. Better understanding of these antagonists may lead to targeted biocontrol of spoilage flora and foodborne pathogens.

Bacteriocinogenic activity of lactobacilli from fermented sausages

During the screening of the inhibitory activity of 254 strains of lactobacilli isolated from fermented sausages at different times of ripening, 22% of the strains showed inhibition that was not related to acid or hydrogen peroxide, towards one or more indicator strains. Not all the strains were capable of secreting the inhibitory compound in the supernatant fluid. The characterization of the inhibitory compound from three strains showed that they were bacteriocins with a bactericidal mode of action and a molecular weight exceeding 10,000 Da. Lactobacillus plantarum CTC 305, CTC 306 and Lact. sake CTC 372 inhibited Listeria monocytogenes. Lactobacillus sake CTC 372 was cured of two plasmids of 84.8 kbp and 41.3 kbp, losing the production and the immunity of a bacteriocin as well as the ability to ferment lactose.

Characterization of bacteriocin produced by Pediococcus pentosaceus from wine

Twenty strains of Pediococcus pentosaceus isolated from wine were examined for production of bacteriocins. Only two of them showed inhibitory activity, Ped. pentosaceus N4p against the indicator strains of the same species and N5p against 19 strains of the three genera of lactic acid bacteria from wine. The antimicrobial substance from N5p strains was removed by membrane (0.2 micron) filtration, destroyed by organic solvents and proteolytic enzymes. It was stable for 60 min at 100 degrees C. The bacteriocin was produced early in the growth cycle and its production was maximum after 48 h of culture in tomato juice medium at an initial pH of 6.5. The bactericidal effect was observed.

Sakacin M, a bacteriocin-like substance from Lactobacillus sake 148

The antagonistic activity of Lactobacillus sake 148 was evaluated during its growth on complex broth media and in a semisynthetic defined medium (SDM) with various supplements. The antagonistic activity was a growth-associated property, being detected and quantified when L. sake 148 was grown at either 4, 8, 16, 25 or 32 degrees C. The concentrated culture supernatant of L. sake 148 was subjected to purification by lyophilization and gel filtration. The purification procedure resulted in a small increase in its specific activity (7-fold) and in a low recovery of the original inhibitory activity (8%). Gel filtration analysis of the partially purified activity on Sephadex G-50 revealed an apparent molecular weight of 4640. The partially purified antagonistic activity of L. sake 148 was destroyed by treatment with proteolytic enzymes. However, the antagonistic activity was resistant to heat, having D-values at 121, 135 and 150 degrees C of 23.8, 17.4 and 15.2 min, respectively.

Production of an Amylase-Sensitive Bacteriocin by an Atypical Leuconostoc paramesenteroides Strain

An atypical Leuconostoc paramesenteroides strain isolated from retail lamb produced a bacteriocin, leuconocin S, that was inactivated by α-amylase, trypsin, α-chymotrypsin, protease, and proteinase K but not by lipase or heat treatment at 60°C for 30 min. Supernatants from culture broths produced two glycoprotein bands on sodium dodecyl sulfate-polyacrylamide gels; these had molecular weights of 2,000 and 10,000 and activity against Lactobacillus sake ATCC 15521. The crude bacteriocin preparation was bacteriostatic and dissipated proton motive force. Bacteriocin activity was produced over a wide pH range (5.2 to 7.9) on buffered agar medium, with an optimum pH of pH 6.15. The optimum pH for production in broth was 6.5 to 7.0.

Comparison of probiotic and antibiotic intramammary therapy of cattle with elevated somatic cell counts

The effects of treating subclinical mastitis with intramammary infusions of either a Lactobacillus or an antibiotic preparation on intramammary infection cure rate and on milk SCC were compared. Cows with two consecutive monthly DHIA composite SCC greater than 300,000 cells/ml (5.4771 log10/ml) were defined as high SCC cows. Twenty-six subclinical cows were randomly assigned to one of two treatments. Quarter foremilk samples were obtained from all quarters at d 0, 7, and 14 following infusion to determine the microbiological status and SCC. Composite milk SCC were determined monthly by DHIA and at d 0, 7, and 14 of the study. Coagulase-negative staphylococci were the predominantly isolated pathogens. Treatment of cows with Lactobacillus cured 21.7% of infected quarters, whereas 73.7% of infections treated with antibiotic were eliminated. Treatment of quarters with antibiotic did not reduce quarter SCC unless infected quarters were cured. Intramammary infusion of quarters with Lactobacillus increased quarter SCC, mainly because of an increase in SCC of initially uninfected, low SCC quarters. Monthly composite SCC were similar between treatments. The results indicate that administering Lactobacillus or antibiotic treatment to all quarters based on elevated composite SCC should not be adopted. Lactobacillus treatment increased SCC with no effect on infection rate.

Antibiosis between bacteria isolated from the vagina of women with and without signs of bacterial vaginosis

Lactobacilli from women with and without bacterial vaginosis (BV) were tested for H2O2 production. Thirty-seven (79%) of the 47 strains of lactobacilli isolated from the women without BV produced H2O2, while only nine (23%) of the 39 strains of lactobacilli obtained from women with BV did so. Five of 20 H2O2-producing and two of 26 non-producing strains of Lactobacillus exhibited antibiosis against four of 12 strains of peptostreptococci and two of 10 strains of Mobiluncus spp. None of a further 41 different anaerobic and facultative anaerobic bacterial strains were inhibited by any of the isolates of lactobacilli tested. Some strains of Gardnerella vaginalis, Bacteriodes spp., Mobiluncus spp. and Peptostreptococcus spp. inhibited the growth of three strains of lactobacilli belonging to different species. When the pH of the culture medium was increased from 6.0 to 6.5 this led to a decrease in the number of strains inhibited and/or the size of the growth-inhibitory zones. Different concentrations of H2O2 did not inhibit any of the strains tested. The growth-inhibitory effect of lactobacilli could not be related to their bacteriocin production. Increasing the iron content of the medium by adding FeCl3 (0.01 mM-1 mM) decreased or completely abolished the antibiosis.

Public health implication of refrigerated pasteurized ('sous-vide') foods

Food that upon pasteurization is stored in hermetically sealed containers at food temperatures not exceeding 3 degrees C could be designated by the generic term Refrigerated Pasteurized Foods of Extended Durability, REPFEDs. If not properly processed or protected against recontamination, or if temperature-abused, REPFEDs may present serious health risks. However, control is readily available. Sound microbial ecology, supported by expert risk assessment, allows the design and introduction of longitudinally integrated manufacture, distribution, handling by outlets and consumers and culinary preparation, which result in the assurance of the wholesomeness of the commodity as eaten. Recent progress, including intrinsic preservation by the incorporation of starter cultures, bacteriocins or particular enzymes, opens vistas for attractive future developments. Once microbiological safety has been built into the REPFED-line, monitoring can be limited to (i) real-time tests particularly applied to the factory environment; and (ii) rapid, simple examination for marker organisms of freshly manufactured products versus those approaching expiration dates. Such audits will allow rapid retrieval of incidental process failure and its rectification. It also serves to substantiate measurements of food temperature and spot checks on intrinsic inhibitory attributes. The application of scientific knowledge and technological expertise should primarily be entrusted to the industry itself, heeding Lord Plumb's strategy of "partnership along the food production chain from farm to fork." It should be supported and validated by Public Health Authorities. At all stages safety communication with the public should be ensured.