anti-Listeria Activity Research Articles

Impairment of the class IIa bacteriocin receptor function and membrane structural changes are associated to enterocin CRL35 high resistance in Listeria monocytogenes.

Enterocin CRL35 is a class IIa bacteriocin with anti-Listeria activity. Resistance to these peptides has been associated with either the downregulation of the receptor expression or changes in the membrane and cell walls. The scope of the present work was to characterize enterocin CRL35 resistant Listeria strains with MICs more than 10,000 times higher than the MIC of the WT sensitive strain. Listeria monocytogenes INS7 resistant isolates R2 and R3 were characterized by 16S RNA gene sequencing and rep-PCR. Bacterial growth kinetic was studied in different culture media. Plasma membranes of sensitive and resistant bacteria were characterized by FTIR and Langmuir monolayer techniques. The growth kinetic of the resistant isolates was slower as compared to the parental strain in TSB medium. Moreover, the resistant isolates barely grew in a glucose-based synthetic medium, suggesting that these cells had a major alteration in glucose transport. Resistant bacteria also had alterations in their cell wall and, most importantly, membrane lipids. In fact, even though enterocin CRL35 was able to bind to the membrane-water interface of both resistant and parental sensitive strains, this peptide was only able to get inserted into the latter membranes. These results indicate that bacteriocin receptor is altered in combination with membrane structural modifications in enterocin CRL35-resistant L. monocytogenes strains. Highly enterocin CRL35-resistant isolates derived from Listeria monocytogenes INS7 have not only an impaired glucose transport but also display structural changes in the hydrophobic core of their plasma membranes.

Anti-Listeria Activity of Lactic Acid Bacteria in Two Traditional Sicilian Cheeses.

Listeria monocytogenes is a pathogen frequently found in dairy products, and its growth is difficult to control. Bacteriocin-like inhibitory substances (BLIS), produced by lactic acid bacteria (LAB), having proven in vitro anti-Listeria activity, could provide an innovative approach to control L. monocytogenes; however, this application needs to be evaluated in vivo. In this study, twenty LAB strains isolated from different Sicilian dairy environments were tested for control of growth of L. monocytogenes in three different experimental trials. First, raw and UHT milk were inoculated with LAB strains alone, and LAB strains mixed with L. monocytogenes. Second, mini-cheeses containing LAB and/or L. monocytogenes were produced. Third, two traditional Sicilian cheeses inoculated with a multi-strain LAB mixture combined with L. monocytogenes were produced. The addition of BLIS produced by LAB to milk and in mini-cheese production was unable to inhibit the growth of L. monocytogenes. However, an anti-Listeria effect was observed in the Pecorino Siciliano cheeses, where, after 15 days of ripening, the cheeses with added LAB had fewer L. monocytogenes compared to the control cheeses with no added LAB, while in the Vastedda della valle del Belìce cheeses, the multi-strain LAB mixture completely prevented the growth of L. monocytogenes.

Anti-Listeria Activity of Bioactive Food Packaging on Artificially Contaminated Sliced Cheese

The aims of this study were to (1) study the optimal growth condition for two Lactococcus lactis strains to produce the anti-listeria compounds and (2) evaluate the effect of films activated with a twofold concentrated cell-free supernatant of La. lactis to inhibit Listeria monocytogenes. For the growth conditions, skimmed milk added to either Ml7 or MRS provided the highest levels of anti-listeria activity assayed (800 arbitrary unit per milliliter) for both La. lactis strains. A significant decrease of Li. monocytogenes counts was observed in cheese packed in films treated with an average decrease of 2.12 log colony-forming unit per gram after 15 days of storage. Practical Applications The antimicrobial film for food packaging can be used for the preservation of perishable foods such as the sliced cheese. This film developed in our study inhibits Listeria monocytogenes growth in sliced cheese, and does not have an adverse effect on the lactic microbiota, contributing to the preservation of the quality of the product. Thus, it could be a useful tool for the control of the development of pathogens in foods during storage of dairy products.

Characterization of lactic acid bacteria isolated from wheat bran sourdough

Spontaneously fermented foods, such as sourdough, represent a source of lactic acid bacteria with potential interesting functional and technological properties as well as a potential source of probiotics. The choice of the starter cultures has a critical impact on the palatability, processability and nutritional attributes of fermented products. The aim of this study was to characterize the predominant microbial species previously isolated from a sourdough-like spontaneous fermented wheat bran. Lactic acid bacteria, such as Leuconostoc mesenteroides, Leuconostoc citreum, Lactobacillus brevis, Lactobacillus curvatus, Lactobacillus sakei, Lactobacillus plantarum and Pediococcus pentosaceus, were phenotypically characterized by their growth and acidification rate, carbohydrate metabolism, antifungal activity, exopolysaccharide production, as well as safety. The strains were also tested for xylan- and phytate-degrading activities. Moreover, probiotic properties, such as acid and bile tolerance, anti-listeria activity and adhesion ability to Caco-2 cells were examined. L. plantarum CE42, CE60 and P. pentosaceus CE65, CE23 showed interesting technological application potential due to their antifungal activity and exopolysaccharide production. Some strains also exhibited phytate degrading activity and could be exploited to improve mineral bioavailability of fermented products. Moreover, P. pentosaceus CE65 seems to be a candidate for use as probiotic.

Characterization of a two-peptide plantaricin produced by Lactobacillus plantarum MBSa4 isolated from Brazilian salami

The aim of this study was to explore the biochemical and genetic features of the two-peptide bacteriocin produced by a Lactobacillus plantarum strain isolated from Italian type salami produced in Brazil (Lb. plantarum MBSa4). Identification of bacteriocinogenic Lb. plantarum MBSa4 was performed by 16S rRNA sequencing. Expressed bacteriocin was evaluated for spectrum of activity, heat and pH stability, mechanism of action, and molecular mass. Partial purification was achieved by cation-exchange, and reversed phase - HPLC. Total DNA of Lb. plantarum MBSa4 was extracted and tested for presence of previously described bacteriocin genes. Bacteriocin MBSa4 was heat-stable, unaffected by pH 2.0 to 6.0 and active against all tested Listeria monocytogenes strains and most of tested fungi. Maximal production (1600 AU/ml) in MRS broth occurred after 22 h at 25 °C, presenting bacteriostatic activity as result of combined action of two components. The molecular mass determined by SDS-PAGE was 2.3 kDa. PCR-amplified DNA indicated the same nucleotide sequence of plantaricin W. Results indicate that Lb. plantarum MBSa4 produces plantaricin W, a two-peptide lantibiotic with remarkable anti-Listeria activity.

Controlling Listeria monocytogenes in Cold Smoked Salmon with the Antimicrobial Peptide Salmine.

Listeria monocytogenes (LM) is a major safety concern for smoked salmon producers, as it can survive both the brining and smoking process in cold smoked salmon production. Salmine is a cationic antimicrobial peptide derived from the milt of salmon that has been shown to inhibit the growth of LM in vitro. Commercialization of this peptide would add value to a waste product produced when raising salmon. The purpose of this study was to determine the anti-listeria activity of salmine in smoked salmon by measuring the viable counts of LM over time. Cold smoked salmon was treated with a salmine solution or coated with agar or k-carrageenan films incorporating salmine to maintain a high surface concentration of the antimicrobial. Samples were then inoculated with approximately 1.0×10(3) cells of LM. The viable counts were then enumerated throughout 4 wk at 4 °C storage. It was found that 5 mg/g salmine delayed the growth of LM on smoked salmon. These samples had significantly (P<0.05) lower LM counts than on the untreated samples on days 13 and 22. Edible films did not significantly (P > 0.05) improve the antimicrobial efficacy of salmine. The peptide combined with biopolymers also had lower antimicrobial activity in vitro when compared to salmine alone. These results suggest there is potential for salmine to be used as a natural hurdle to inhibit growth of LM due to post process contamination; however, future investigations for extending this effect throughout the shelf life of smoked salmon products are warranted.

Biotechnical paving of recombinant enterocin A as the candidate of anti-Listeria agent.

BackgroundEnterocin A is a classic IIa bacteriocin isolated firstly from Enterococcus faecium CTC492 with selective antimicrobial activity against Listeria strains. However, the application of enterocin A as an anti-Listeria agent has been limited due to its very low native yield. The present work describes high production of enterocin A through codon optimization strategy and its character study.ResultsThe gene sequence of enterocin A was optimized based on preferential codon usage in Pichia pastoris to increase its expression efficiency. The highest anti-Listeria activity reached 51,200 AU/ml from 180 mg/l of total protein after 24 h of induction in a 5-L fermenter. Recombinant enterocin A (rEntA), purified by gel filtration chromatography, showed very strong activity against Listeria ivanovii ATCC 19119 with a low MIC of 20 ng/ml. In addition, the rEntA killed over 99% of tested L. ivanovii ATCC19119 within 4 h when exposed to 4 × MIC (80 ng/ml). Moreover, it showed high stability under a wide pH range (2–10) and maintained full activity after 1 h of treatment at 80°C within a pH range of 2–8. Its antimicrobial activity was enhanced at 25 and 50 mM NaCl, while 100–400 mM NaCl had little effect on the bactericidal ability of rEntA.ConclusionThe EntA was successfully expressed in P. pastoris, and this feasible system could pave the pre-industrial technological path of rEntA as a competent candidate as an anti-Listeria agent. Furthermore, it showed high stability under wide ranges of conditions, which could be potential as the new candidate of anti-Listeria agent.

Improving safety of salami by application of bacteriocins produced by an autochthonous Lactobacillus curvatus isolate

The aims of this study were to isolate LAB with anti-Listeria activity from salami samples, characterize the bacteriocin/s produced by selected isolates, semi-purify them and evaluate their effectiveness for the control of Listeria monocytogenes during manufacturing of salami in a pilot scale. Two isolates (differentiated by RAPD-PCR) presented activity against 22 out of 23 L. monocytogenes strains for bacteriocin MBSa2, while the bacteriocin MBSa3 inhibited all 23 strains in addition to several other Gram-positive bacteria for both antimicrobials and were identified as Lactobacillus curvatus based on 16S rRNA sequencing. A three-step purification procedure indicated that both strains produced the same two active peptides (4457.9 Da and 4360.1 Da), homlogous to sakacins P and X, respectively. Addition of the semi-purified bacteriocins produced by Lb. curvatus MBSa2 to the batter for production of salami, experimentally contaminated with L. monocytogenes (104–105 CFU/g), caused 2 log and 1.5 log reductions in the counts of the pathogen in the product after 10 and 20 days respectively, highlighting the interest for application of these bacteriocins to improve safety of salami during its manufacture.

Preservation of viability and anti-Listeria activity of lactic acid bacteria, Lactococcus lactis and Lactobacillus paracasei, entrapped in gelling matrices of alginate or alginate/caseinate

Abstract In order to control undesirable microorganisms growth in foods, the performance of alginate and alginate–caseinate (an aqueous two-phase system) matrices entrapping lactic acid bacteria (LAB) ( Lactobacillus paracasei LAB1 and Lactococcus lactis LAB3) was investigated. Polymeric matrices were initially loaded with LAB cells at ∼10 8−10 or ∼10 4−6 CFU mL −1 , and were monitored, in liquid and gelled form (beads), for 12 days at 30 °C. In the liquid form, maximum cell density (∼10 9 CFU mL −1 ) was reached after 24 h whatever the matrix. Then, the LAB population decreased but remained higher in alginate–caseinate matrices: 10 7 and 10 6 CFU mL −1 of LAB3 cells were enumerated after 12 days in alginate–caseinate and in alginate matrices, respectively. Anti- Listeria activity (assayed by agar well diffusion method) did not vary much over 12 days and was also higher for cells entrapped in alginate–caseinate matrices. When matrices were gelled, similar trends were observed: at “Day 12”, LAB3 population was 10 4−5 and 10 2−3 CFU/bead, and, LAB1 population was 10 5−6 and 10 3−4 CFU/bead, in alginate–caseinate and alginate beads, respectively. Antimicrobial activity of alginate–caseinate beads containing LAB1 cells was quite constant over 12 days. The anti- Listeria activity of LAB cell-free supernatants incorporated in matrices with caseinate was also higher. In fact, the presence of caseinate was shown to promote both the survival of LAB cells and the release of their antimicrobial metabolites. Observation of liquid and gelled matrices by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) revealed a preferential localization of LAB cells in casein-rich microdomains which could affect favorably the efficiency of bipolymeric matrices.

Anti-Listeria Starters: In Vitro Selection and Production Plant Evaluation

Anti-Listeria bacterial starters are highly demanded by the meat industry. Novel bioprotective anti-Listeria starters were searched among Lactobacillus species strains isolated from artisanal sausages. The screening confirmed that anti-Listeria activity is a strain-specific property and yielded only 1 strain (of 36) exhibiting a satisfactory level of inhibition, L. delbrueckii WC0286. This strain was compared with two commercial bioprotective starters, SafePro B-SF-43 and SafePro B-LC-20, in a model simulating in vitro the first step of the fermentation process. The presence of the bioprotective starters did not modify the pH in such a way that could affect the safety or organoleptic properties of the product. Both SafePro B-SF-43 and SafePro B-LC-20 effected an important reduction of Listeria counts (0.56 and 0.72 log CFU g(-1), respectively, in 72 h), while the anti-Listeria effect of L. delbrueckii WC0286 was minor (0.15 log CFU g(-1)). These results discouraged the utilization of L. delbrueckii WC0286 for a challenge test in a pilot salami production, in favor of the best-performing bioprotective starter, SafePro B-LC-20. The test confirmed that SafePro B-LC-20 did not alter the acidification trend of sausages and was capable of inhibiting Listeria, which decreased by 1.21 log CFU g(-1). This information is relevant to address research activity toward the development of new bioprotective starters. The data herein presented demonstrate that the efficacy in Listeria control of potentially bioprotective bacterial starters requires further validation in real meat matrixes, possibly by using in vitro meat fermentation experiments to narrow down the list of candidates before pilot scale challenge tests.

Gas chromatography-mass spectrometry characterisation of the anti-Listeria components of Garcinia kola seeds

Adsorption chromatography was used to separate the bioactive constituents of the crude n-hexane extract of Garcinia kola seeds. The silica gel 60 column fractions were eluted using the solvent combination of benzene: ethanol : ammonium hydroxide (BEA) in the ratio combination of 36 : 4 : 0.4 v/v. The fractions were tested for anti-Listeria activities by determining their MIC50, MIC90 or MIC against 4 Listeria isolates. The fractions were labelled BEA1 to BEA5 and 3 out of the 5 fractions eluted were active against the test Listeria species with MIC's ranging from MIC 0.57 mg/mL to MIC50 0.625 mg/mL. The most active fractions, BEA2 and BEA3, were subjected to gas chromatography coupled to mass spectrometry (GC-MS) to identify their composition. Fraction BEA2 constituted of 18 compounds mostly sterols and the BEA3 fraction contained 27 compounds with the most abundant compounds being fatty acids derivatives. The BEA2 fraction's interactions with antibiotics proved to be 100% synergistic with ciprofloxacin and ampicillin whilst it exhibited 50% additivity and 50% synergism with penicillin G. However, all the interactions of the BEA2 fraction with each of the conventional antibiotics used were synergistic against the human listeriosis causative bacteria Listeria monocytogenes.

Development of an active wheat gluten film with Lactobacillus curvatus CRL705 bacteriocins and a study of its antimicrobial performance during ageing

Antimicrobial wheat gluten film was obtained at pilot scale by Lactobacillus curvatus CRL705 bacteriocins inclusion in the film-forming solution. Bacteriocins’ minimum inhibitory concentration for the film activation was 2133 AU cm−3 (lactocin AL705) and 267 AU cm−3 (lactocin 705). Mechanical and barrier properties as well as film ageing kinetics were not significantly affected by the addition of bacteriocins. The antimicrobial film performance during ageing was assessed. Film activity against Listeria innocua 7 and Lactobacillus plantarum CRL691 was observed over 50 days of ageing. Even when the release of bacteriocins from the film upon water contact was observed for both bacteriocins at the beginning of the ageing period, and anti-Listeria activity was delivered to the simulant up to the 15th day of ageing, film residual activity for both bacteriocins was observed over 50 days. The results confirm the potential of a gluten film doped with L. curvatus CRL705 bacteriocins as a carrier of bacteriocins to avoid Listeria and lactic acid bacterial growth, thus enhancing quality and safety in foods.

Anti-listeria activity of poly(lactic acid)/sawdust particle biocomposite film impregnated with pediocin PA-1/AcH and its use in raw sliced pork

A novel poly(lactic acid) (PLA)/sawdust particle (SP) biocomposite film with anti-listeria activity was developed by incorporation of pediocin PA-1/AcH (Ped) using diffusion coating method. Sawdust particle played an important role in embedding pediocin into the hydrophobic PLA film. The anti-listeria activity of the PLA/SP biocomposite film incorporated with Ped (PLA/SP+Ped) was detected, while no activity against the tested pathogen was observed for the control PLA films (without SP and/or Ped). Dry-heat treatment of film before coating with Ped resulted in the highest Ped adsorption (11.63±3.07μgprotein/cm2) and the highest anti-listeria activity. A model study of PLA/SP+Ped as a food-contact antimicrobial packaging on raw sliced pork suggests a potential inhibition of Listeria monocytogenes (99% of total listerial population) on raw sliced pork during the chilled storage. This study supports the feasibility of using PLA/SP+Ped film to reduce the initial load of L. monocytogenes on the surface of raw pork.

Production, stability, gene sequencing and in situ anti-Listeria activity of mundticin KS expressed by three Enterococcus mundtii strains

Three enterococci (WFE3, WFE20 and WFE31) selected as presumptive bacteriocin producers were found to be active against Listeria monocytogenes. In this study, due to their potential industrial/food applications, the three bacterial isolates were extensively characterized. Identification was performed by means of a combined 16S rRNA gene sequencing and multiplex PCR approach, and was confirmed with the sequencing of a partial region of a protein-encoding gene, namely pheS. The three isolates belonged unequivocally to the species Enterococcus mundtii. The randomly amplified polymorphic DNA (RAPD) analysis recognized three distinct strains. The supernatants were mainly active against Listeria spp., but some lactic acid bacteria were also inhibited. The proteinaceous nature of the three supernatants was detected after treatment with proteinase K, protease B and trypsin. The bacteriocins were found to be heat resistant, stable in a large pH range and in presence of ethanol. The bacteriocins were not adsorbed onto the surface of the producer cells and their effect was bactericidal. The production of bacteriocins was higher at neutral pHs and temperatures in the range 30–37°C. The active supernatants did not show cytotoxicity against human erythrocytes and the three strains were susceptible to the action of common antibiotics. The genetic characterization of the bacteriocin genes showed that all three strains produced mundticin KS. They produced it in five food model systems, sterilized by thermal treatment or filtration, prepared from fresh vegetables, cereals, cheeses, meats and fishes. The in situ anti-listerial activities of the strains WFE3, WFE20 and WFE31 were quantitatively different.

Adsorption of the bacteriocins produced by Lactobacillus curvatus CRL705 on a multilayer-LLDPE film for food-packaging applications

Adsorption of bacteriocins produced by Lactobacillus curvatus CRL705, lactocin 705 (whose activity depends upon complementation of two peptides, lac705α and lac705β) and bacteriocin/s with strong anti-Listeria activity, on a multilayer film was investigated. Lactocin 705 adsorption equilibrium at 30 °C was reached from 1 h of film contact. This bacteriocin exhibited a Langmuir-type adsorption, showing a mass adsorption maximum of 0.72 ± 0.05 μg cm−2 and a minimum inhibition concentration of 1 μg ml−1. The influence of impurities, generated from bacteriocinogenic strains growth, on bacteriocins adsorption to the film was investigated by inhibition area evaluation in semisolid agar. Impurities from LAB growth strongly influenced adsorption and lactocin 705 antimicrobial activity on the film, while antilisterial bacteriocin/s adsorption remained unaffected. To explain these results, a lack of lac705β and lac705α peptides complementation necessary for antimicrobial activity, while no interactions among impurities and antilisterial bacteriocin/s during adsorption was suggested. Antilisterial bacteriocin/s activity on the film was not influenced by lactocin 705 adsorption; conformational reorganization of adsorbed antilisterial bacteriocin/s in the presence of lactocin 705 could allow the adsorption of both bacteriocins while maintaining antilisterial antimicrobial activity. This study highlights the technological importance of adsorption optimization to obtain effective antimicrobial food packaging systems.

Inhibitory activity of surfactin, produced by different Bacillus subtilis subsp. subtilis strains, against Listeria monocytogenes sensitive and bacteriocin-resistant strains

Three surfactin-producing Bacillus subtilis strains, C4, M1 and G2III, previously isolated from honey and intestines from the Apis mellifera L. bee, were phylogenetically characterized at sub-species level as B. subtilis subsp. subtilis using gyrA gene sequencing. The antagonistic effect of surfactin was studied against seven different Listeria monocytogenes strains, 6 of which were resistant to bacteriocins. Surfactin showed anti-Listeria activity against all 7 strains and a dose of 0.125mg/mL of surfactin was enough to inhibit this pathogen. Surfactin sintetized by B. subtilis subsp. subtilis C4 inhibited the pathogen in lower concentrations, 0.125mg/mL, followed by G2III and M1 with 0.25 and 1mg/mL, respectively. In particular, a dose of 0.125mg/mL reduced the viability of L. monocytogenes 99/287 RB6, a bacteriocin-resistant strain, to 5 log orders. Surfactin assayed maintained anti-Listeria activity within a pH range of between 2 and 10, after heat treatment (boiling for 10min and autoclaving at 121°C for 15min) and after treatment with proteolytic enzymes. These results suggest that surfactin can be used as a new tool for prevention and the control of L. monocytogenes in different environments, for example, in the food industry.

Anti-Listeria monocytogenes activity of enterocins microencapsulated by ionic gelation

The encapsulation of enterocins synthesized by Enterococcus faecium CRL1385 through ionic gelation with calcium ions was analyzed. Different enterocins samples were lyophilised and encapsulated using low-methoxyl pectin as the coating material. Lipids present in milk butter were also added to control the release of antimicrobial peptides from the capsules. The morphology of fresh and freeze-dried capsules was examined using light microscopy and scanning electron microscopy, respectively. Antimicrobial activity of encapsulated bacteriocins was assessed against Listeria monocytogenes 01/155 using the agar diffusion technique and direct contact in microplates. The capsules with higher lipid content showed a more spherical and uniform shape. Pathogen inhibition was observed for capsules prepared with different bacteriocin solutions both on solid (halo diameter = 8.5–13.5 mm) and in an aqueous medium (ca. 2 log orders decline in L. monocytogenes viability). The outcomes suggest that bacteriocin encapsulation through ionic gelation can be a potential alternative for the application of these antimicrobial peptides as biopreservatives in food.

Anti-Listeria activity of lactic acid bacteria isolated from golka, a regional cheese produced in Poland

Eight hundred lactic acid bacteria (LAB) strains isolated from golka, one of the oldest and most popular regional cheese produced in Poland, were screened for anti-Listeria activity.Nearly one third of isolates showed antagonistic activity against Listeria monocytogenes. Seven strains produced other substances active against L. monocytogenes. These substances were detected in neutralized cell-free supernatant fluids and were classified as bacteriocins. 16S rDNA identification of the selected bacteriocin-producing bacteria was performed. By using primers specific to a fragment of class IIa bacteriocin-coding genes, developed by the authors, presence of the bacteriocin structural gene was confirmed for all Lactococcus garvieae strains, Leuconostoc mesenteroides 453Lab and Lactobacillus plantarum Lab572. Presence of the class IIa bacteriocin-coding genes within genomes of non-bacteriocin-producing strains Lactococcus lactis subsp. lactis was also detected. Bacteriocins with the highest activity against Listeria, i.e. bacteriocins of L. garvieae Lab428, Lc. mesenteroides Lab25 and Lb. plantarum Lab572 strains, were partially characterized. The bacteriocins did not adhere to surface of the producer cells and exhibit a bactericidal mode of action. Bacteriocin of L. garvieae 428Lab was produced at much higher levels (12.800 AU/ml), as compared to the other bacteriocins (3.200 AU/ml).Our results indicate that golka cheese is a rich source of LAB active against L. monocytogenes. The bacteriocinogenic isolates from golka described in this work may potentially find application as starter or protective cultures and could constitute a superb genetic pool for production of new bacteriocins.

Isolation and characterization of bacteriocin with anti-listeria and anti-MRSA activity produced by food and soil isolated bacteria

The search for a novel peptide-based antibiotic as replacement for currently used antibiotics is promising as it seems to develop less resistant compared to that of other type of antibiotic. Eighteen different food and soil samples were used for screening of a novel bioactive peptide producing bacteria. Among 1,265 isolated bacteria, one hundred and sixty seven isolated colonies showed antibacterial activity against methicillin resistantStaphylococcus aureus (MRSA) and Listeria monocytogenes by co-culture method. The activity of partially purified bacteriocin or PPB prepared from three isolated strains, CR-1-2L, SP-1-36LM and SO-4-1LM against L. monocytogenes were 105 AU/ml, 2000 AU/ml and 1000 AU/ml, respectively. PPB from three isolated bacteria showed narrow inhibition as they are active only against gram positive bacteria. PPB produced by CR-1-2L, SP-1-36LM and SO-4-1LM was heat stable up to 100°C for 60 min and active within the pH range of 3-9. The activity of PPB prepared from three isolated strains CR-1-2L, SP-1-36LM and SO-4-1LM disappeared when treated with proteinase K, chymotrypsin and trypsin demonstrating their proteinaceous nature. These three isolated strains can be regarded as bacteriocin producing bacteria or BAC. They were all identified as Bacillus sp.by 16S rRNA gene sequence. The effect of PPB prepared from strain SO-4-1LM was bactericidal to L. monocytogenes and the highest activity was found at six hours after incubation. Tris-Tricine SDS-PAGE analysis revealed that the bacteriocin prepared fromBacillus sp. SO-4-1LM had an apparent molecular weight of 2.5 kDa. The bioactive peptide from these three isolated bacteria has a potential for use as an alternative antibacterial agent for the treatment of infection with MRSA and/or use in the food industry in the future. Key words: Bacteriocin, anti-MRSA, anti-listeria, Bacillus sp.

Anti-listeria activity of Pediococcus pentosaceus BCC 3772 and application as starter culture for Nham, a traditional fermented pork sausage

Lactic acid bacteria forming bacteriocin active against Listeria monocytogenes were screened for potential use in controlling growth of L. monocytogenes in Nham, a Thai traditional fermented pork sausage. Based on the spot-on-lawn assay, Pediococcus pentosaceus BCC 3772 was found to produce the highest anti-listeria activity. Through a series of chromatographic techniques, Edman N-terminal sequencing and mass spectrometry, this anti-listeria compound showed a complete homology to pediocin PA-1/AcH. Inoculation of P. pentosaceus BCC 3772 in Nham caused a significant decrease of 3.2 log in population of spiked L. monocytogenes within 18–24 h of fermentation, in comparison with the initial count with no significant changes in sensory properties and consumer acceptability on the overall characteristics of the final fermented Nham products. These results indicate that the P. pentosaceus BCC 3772 should be useful as a functional starter culture for control of L. monocytogenes without compromising the unique quality of Nham.