A new repertoire of informations about the quorum sensing system in Salmonella enterica serovar Enteritidis PT4.

Salmonella spp are among the main causative agents of foodborne diseases. Some phenotypes associated with increased drug resistance and virulence are regulated by quorum sensing (QS). In the present study, the autoinducer (AI)-1- and -2-mediated QS mechanisms were characterized in Salmonella enterica serovar Enteritidis PT4 for the first time. Salmonella Enteritidis did not produce AI-1. Phylogenetic analysis of nucleotides encoding the SdiA protein, the response regulator of AI-1-mediated QS, and comparative alignment of its amino acids showed that the gene and protein are conserved within the same bacterial genus. Thus, bacteria of the same genus respond to the same AIs. However, this finding did not preclude the possibility that Salmonella Enteritidis might respond to AIs released from bacteria of a different genus, which might confer a competitive advantage to this pathogen. We found that the regulation of AI-2-mediated QS in Salmonella Enteritidis is similar to that in serovar Typhimurium. The elucidation of the AI-1- and AI-2-mediated QS mechanisms in Salmonella Enteritidis will contribute to the development of new control strategies for this pathogen by indicating new targets for antimicrobial drugs

Riboflavin excretion by Pachysolen tannophilus grown in synthetic medium supplemented with g-xylose

Pachysolen tannophilus excreted riboflavin (12.7 m g/ml) into a synthetic medium withd-xylose as carbon source, when the pH was below 2.0. The addition of glucose enhanced the quantity of riboflavin excreted. The greatest riboflavin production was at pH 1.6 after 5 days at 30°C

Potential virulence of Klebsiella sp. isolates from enteral diets

We aimed to evaluate the potential virulence of Klebsiella isolates from enteral diets in hospitals, to support nosocomial infection control measures, especially among critical-care patients. Phenotypic determination of virulence factors, such as capsular expression on the external membrane, production of aerobactin siderophore, synthesis of capsular polysaccharide, hemolytic and phospholipase activity, and resistance to antibiotics, which are used therapeutically, were investigated in strains of Klebsiella pneumoniae and K. oxytoca. Modular industrialized enteral diets (30 samples) as used in two public hospitals were analyzed, and Klebsiella isolates were obtained from six (20%) of them. The hypermucoviscous phenotype was observed in one of the K. pneumoniae isolates (6.7%). Capsular serotypes K1 to K6 were present, namely K5 and K4. Under the conditions of this study, no aerobactin production, hemolytic activity or lecithinase activity was observed in the isolates. All isolates were resistant to amoxicillin and ampicillin and sensitive to cefetamet, imipenem, chloramphenicol, gentamicin and sulfamethoxazole-trimethoprim. Most K. pneumoniae isolates (6/7, 85.7%) from hospital B presented with a higher frequency of resistance to the antibiotics tested in this study, and multiple resistance to at least four antibiotics (3/8; 37.5%) compared with isolates from Hospital A. The variations observed in the antibiotic resistance profiles allowed us to classify the Klebsiella isolates as eight antibiotypes. No production of broad-spectrum β-lactamases was observed among the isolates. Our data favor the hypothesis that Klebsiella isolates from enteral diets are potential pathogens for nosocomial infections

Stress enhances the sensitivity of Salmonella enterica serovar Typhimurium to bacteriocins

The aim of this study was to evaluate the potential application of bacteriocins against Gram-negative bacteria when associated with others food preservation methods. Salmonella was subjected to heat, cold, acid and chemical (with ethylenediaminetetracetate and trisodium phosphate) stresses. Then, the cells were recovered and subjected to treatment with bacteriocins (500 AU ml 1 ) for 6 h. Heat and cold stress were those that promoted more sensitization to bactericidal activity of nisin. Under the same conditions, bovicin HC5 acted more rapidly than nisin reducing the number of viable cells to undetectable levels after 20 min of treatment. Similar results with use of nisin only were observed after 6 h of treatment. Stress conditions used in food industry, such as temperature and pH, and use of chelating agents or membrane disruptors, sensitized Salmonella Typhimurium cells to bacteriocins produced by lactic acid bacteria, such as nisin and bovicin HC5. Food preservation methods sensitized Gram-negative bacteria to bacteriocins activity, which demonstrate the potential of nisin and bovicin HC5 to inhibit the growth of Salmonella

Bovicin HC5 reduces thermal resistance of Alicyclobacillus acidoterrestris in acidic mango pulp

To test the effect of bovicin HC5 against vegetative cells and endospores of Alicyclobacillus acidoterrestris DSMZ 2498 in synthetic media and in acidic mango pulp. Alicyclobacillus acidoterrestris was grown in synthetic medium at 40°C and pH 4·0. The effect on vegetative cells was assayed by adding bovicin HC5 to synthetic medium (40–160 AU ml−1) or to mango pulp (100 AU ml−1) at various pH values and determining the effect on growth (OD600nm) and viable cell number, respectively. The effect of bovicin HC5 on spore germination and thermal sensitivity of A. acidoterrestris was tested in mango pulp (pH 4·0) containing 80 AU ml−1 of bovicin HC5. Bovicin HC5 was bactericidal against vegetative cells of A. acidoterrestris at different pH values and showed sporicidal activity against endospores of this bacterium. When spores of A. acidoterrestris were heat treated in the presence of bovicin HC5, D-values decreased 77% to 95% compared to untreated controls at temperatures ranging from 80 to 95°C. Bovicin HC5 was bactericidal and sporicidal against A. acidoterrestrsi DSMZ 2498.These results indicated that bovicin HC5 has potential to prevent spoilage of acidic fruit juices by thermocidophilic spore-forming bacteria

Differences in the antibacterial activity of nisin and bovicin HC5 against Salmonella Typhimurium under different temperature and pH conditions

To compare the action of nisin and bovicin HC5 in combination with EDTA on Salmonella Typhimurium under different environmental conditions. Salmonella Typhimurium was treated in BHI broth containing EDTA (1·5 mmol l−1) and nisin or bovicin HC5 (200 AU ml−1) under different pH and temperature conditions, and according to a central composite design with two factors (temperature and pH). Cell viability was evaluated on plate count agar for 48 h. The combination of nisin or bovicin HC5 with EDTA was able to inhibit the growth of Salmonella, but the temperature and pH conditions promoting inhibition were distinct for each bacteriocin. Nisin was bactericidal over a broad range of temperature and pH, while bovicin HC5 was bacteriostatic in most conditions and bactericidal only in specific conditions (pH >6·0 and temperature >30°C). Salmonella Typhimurium did not show tolerance to bovicin HC5 or cross‐tolerance between these lantibiotics. Nisin and bovicin HC5 both inhibited the growth of Salmonella, but the activity of each bacteriocin was differently influenced by environmental conditions. Nisin and bovicin HC5 have the potential to inhibit the growth of Salmonella, but environmental conditions should be considered to establish optimal conditions for its application

Bactericidal effect of bovicin HC5 and nisin against Clostridium tyrobutyricum isolated from spoiled mango pulp

To test the effect of bovicin HC5 – a bacteriocin from Streptococcus bovis HC5 – against the strains of Clostridium tyrobutyricum isolated from canned spoiled mango pulp. Bovicin HC5 [40–160 arbitrary unit (AU) ml−1] reduced the specific growth rate and increased the lag phase duration of the bacterial isolates inoculated in brain heart infusion media at 30°C. The inhibitory activity of bovicin HC5 (100 AU ml−1) in mango pulp was bactericidal and more pronounced at acidic conditions. When C. tyrobutyricum was inoculated into mango pulp with bovicin HC5, gas production was not observed. Cultures that were successively transferred in the presence of sublethal doses of bovicin HC5 did not become resistant. The addition of bovicin HC5 to mango pulp might be effective in preventing deterioration by spoilage bacteria

Effect of bovicin HC5 on growth and spore germination of Bacillus cereus and Bacillus thuringiensis isolated from spoiled mango pulp

Aims: To use bovicin HC5 to inhibit predominant bacteria isolated from spoiled mango pulp.Methods and Results: Bovicin HC5 and nisin were added to brain heart infusion (BHI) medium (40–160 AU ml )1 ) or mango pulp (100 AU ml )1 ) and the growth of Bacillus cereus and Bacillus thuringiensis was monitored. Cultures treated with bovicin HC5 or nisin showed longer lag phases and grew slower in BHI medium. Bovicin HC5 and nisin were bactericidal and showed higher activity in mango pulp at acidic pH values. To determine the effect on spore germination and D values, mango pulp containing bovicin HC5 was inoculated with 10 6 and 10 9 spores per ml )1 , respectively, from each strain tested. Bovicin HC5 reduced the outgrowth of spores from B. cereus and B. thuringiensis, butthermal sensitivity was not affected.Conclusions: Bovicin HC5 was bactericidal against B. cereus and B. thuringien sis isolated from spoiled mango pulp.Significance and Impact of the Study: Bacillus cereus and B. thuringiensis had not been previously isolated from spoiled mango pulp and bovicin HC5 has the potential to inhibit such bacteria in fruit pulps