Bacteriocinogenic Lactic Acid Bacteria Research Articles

Influence of different culture media on the antimicrobial activity of Pediococcus pentosaceus ST65ACC against Listeria monocytogenes.

Pediococcus pentosaceus ST65ACC is a bacteriocinogenic lactic acid bacteria (LAB) isolated from Brazilian artisanal cheese that is capable of inhibiting different food pathogens, mainly Listeria monocytogenes. The production of bacteriocins can be influenced by several growth conditions, such as temperature, pH, and medium composition. This study aimed to evaluate the effect of different culture media on the production of bacteriocins and antimicrobial activity of P. pentosaceus ST65ACC on L. monocytogenes Scott A. The strains were inoculated alone and in coculture in four different media: BHI broth, MRS broth, meat broth, and reconstituted skim milk (RSM) 10% (w/v). The culture media were then incubated at 37°C for 96h, and count analysis, pH measurement, and bacteriocin production were performed at 0, 24, 48, 72 and 96h. L. monocytogenes was inhibited to nondetectable levels in coculture with P. pentosaceus ST65ACC in MRS broth within 96h, consistent with the high production of bacteriocin throughout the analysis period (3,200-12,800 AU/mL). However, lower inhibitory activities of P. pentosaceus ST65ACC on L. monocytogenes Scott A were recorded in BHI, RSM, and meat broth, with low or no production of bacteriocins at the analyzed times. The composition of these culture media may have repressed the production and activity of bacteriocins and, consequently, the antagonist activity of P. pentosaceus ST65ACC on L. monocytogenes Scott A. The results showed that the antimicrobial activity was more effective in MRS broth, presenting greater production of bacteriocins and less variability when compared to the other media analyzed.

Bacteriocinogenic Lacticaseibacillus paracasei strains from Inner Mongolian fermented milk efficiently control pathogenic bacteria in model cheddar-like cheese

Bacteriocins produced by lactic acid bacteria (LAB) consist of a wide range of antimicrobial proteins or peptides which can be used as bio-preservatives to control food-borne pathogens. In this study, bacteriocinogenic LAB strains were isolated from fermented milk in Inner Mongolia, China. These strains exhibited high antimicrobial activity and were identified as Lacticaseibacillus paracasei. The sensitivity of their antimicrobial activity to protease K implies the possible existence of bacteriocins within the culture. Selected L. paracasei strains were subjected to whole genome sequencing and the bacteriocin biosynthetic gene clusters were identified in-silico. To further verify the antimicrobial properties of the isolated strains in controlling food pathogens in model Cheddar-like cheese, they were used as adjunct starter cultures in cheese contaminated with Bacillus cereus and Listeria monocytogenes. The results showed that each of the five strains carries a minimum of three bacteriocins biosynthetic gene clusters. All L. paracasei strains exhibited the ability to inhibit B. cereus and L. monocytogenes and caused a significant log reduction of pathogens during cheese ripening. Additionally, the isolated strains improved cheese texture and flavor to varying degrees. In conclusion, the indigenious L. paracasei present in milk could play an important role in pathogen control and the quality improvement of Cheddar-like cheeses.

Selection and Characterization of Bacteriocinogenic Lactic Acid Bacteria from the Intestine of Gilthead Seabream (Sparus aurata) and Whiting Fish (Merlangius merlangus): Promising Strains for Aquaculture Probiotic and Food Bio-Preservation.

This study sought to evaluate the probiotic properties and the food preservation ability of lactic acid bacteria isolates collected from the intestines of wild marine fishes (gilthead seabream (Sparus aurata) (n = 60) and whiting fish (Merlangius merlangus) (n = 40)) from the Mediterranean sea in the area of Mostaganem city, Algeria. Forty-two isolates were identified as: Enterococcus durans (n = 19), Enterococcus faecium (n = 15), Enterococcus faecalis (n = 4), Lactococcus lactis subp. lactis (n = 3), and Lactobacillus plantarum (n = 1). All isolates showed inhibition to at least one indicator strain, especially against Listeria monocytogenes, Staphylococcus aureus, Paenibacillus larvae, Vibrio alginolyticus, Enterococcus faecalis, Bacillus cereus, and Bacillus subtilis. In all collected isolates, PCR analysis of enterocin-encoding genes showed the following genes: entP (n = 21), ent1071A/B (n = 11), entB (n = 8), entL50A/B (n = 7), entAS48 (n = 5), and entX (n = 1). Interestingly, 15 isolates harbored more than one ent gene. Antimicrobial susceptibility, phenotypic virulence, and genes encoding virulence factors were investigated by PCR. Resistance to tetracycline (n = 8: tetL + tetK), erythromycin (n = 7: 5 ermA, 2 msrA, and 1 mef(A/E)), ciprofloxacin (n = 1), gentamicin (n = 1: aac(6')-aph(2″)), and linezolid (n = 1) were observed. Three isolates were gelatinase producers and eight were α-hemolytic. Three E. durans and one E. faecium harbored the hyl gene. Eight isolates showing safety properties (susceptible to clinically relevant antibiotics, free of genes encoding virulence factors) were tested to select probiotic candidates. They showed high tolerance to low pH and bile salt, hydrophobicity power, and co-culture ability. The eight isolates showed important phenotypic and genotypic traits enabling them to be promising probiotic candidates or food bio-conservers and starter cultures.

Identification of lactic acid bacteria with anti-listeria activity. Characterization and application of a bacteriocinogenic strain in the control of Listeria monocytogenes in cheese.

The purpose of the research paper was firstly to identify bacteriocin-producing lactic acid bacteria characterizing strains with anti-listeria activity and, secondly, to characterize bacteriocin evaluating its in vitro efficiency as a natural preservative and, thirdly, to evaluate the anti-listeria effect of the bacteriocinogenic strain of Lactiplantibacillus plantarum in cheeses and produce an edible film with anti-listerial effect. Of 355 lactic acid bacteria strains tested, two were able to produce bacteriocin against Listeria monocytogenes and were identified as Lactiplantibacillus plantarum and Lactiplantibacillus pentosus. A bactericidal effect of strain QS494 (Lactiplantibacillus plantarum) was observed in the first 8 h, with a reduction of 1.7 log, using cell-free supernatant with Listeria monocytogenes, where viable cells were counted on listeria selective agar. Both strains showed good technological characteristics and were without production of virulence factors. Changes in the pH of the cell-free supernatant obtained from Lactiplantibacillus plantarum did not affect its antimicrobial activity, which remained stable after heat treatments for up to 15 min at 121°C. Inhibitory activity was also observed after 12 weeks of storage at -20°C. In the evaluation of the anti-listeria effect in cheeses, a 3 log reduction in the Listeria monocytogenes count was observed in 120 h in cheeses produced with bacteriocinogenic lactic acid bacteria, while in cheeses produced with non-bacteriocinogenic culture, we observed a 2 log increase in the count. Edible films produced with the addition of precipitate from the cell free supernatant showed an antimicrobial effect against Listeria monocytogenes. Thus, the two strains studied have technological and biosafety potential.

Potential of selected bacteriocinogenic lactic acid bacteria to control Listeria monocytogenes in nitrite-reduced fermented sausages

Potential of selected bacteriocinogenic lactic acid bacteria to control Listeria monocytogenes in nitrite-reduced fermented sausages

Bioprotective cultures and bacteriocins as food preservatives.

Food preservation technologies face the challenge of extending product shelf life applying different factors to prevent the microbiological spoilage of food and inhibit/inactivate food borne pathogens maintaining or even enhancing its quality. One such preservation strategy is the application of bacteriocins or bacteriocin-producer cultures as a kind of food biopreservation. Bacteriocins are ribosomally synthesized small polypeptide molecules that exert antagonistic activity against closely related and unrelated bacteria without harming the producing strain by specific immunity proteins. This chapter aims to contribute to current knowledge about innovative natural preservative agents and their application in the food industry. Specifically, its purpose is to analyze the classification of bacteriocins from lactic acid bacteria (LAB), desirable characteristics of bacteriocins that position them in a privileged place in food biopreservation technology, their success story as well as the bacteriocinogenic LAB in various food systems. Finally, challenges and barrier strategies used to enhance the efficiency of the bacteriocins antimicrobial effect are presented in this chapter.

A comparative study of antagonistic activity spectra of lactic acid bacteria isolated from fermented foods.

The present work aimed to assess the general antagonistic activity against opportunistic pathogens and to compare antagonistic action spectra of lactic acid bacteria (LAB) strains, isolated from Ukrainian traditional fermented foods. Overall, 161 profiles of the antagonistic activity spectrum were obtained from 1056 LAB strains. Among them, 114 profiles were genus-specific and 47 spectra of antagonistic activity were found in LAB strains of different genera. Furthermore, 19 LAB strains were active only against Gram-negative indicator strains and 149 LAB strains only against Gram-positive indicator strains. The size of growth inhibition zones of indicator strains by LAB strains of each genus did not correlate with the level of acidification. Zones of growth inhibition of indicator strains appeared after 6-8 h of incubation and in most cases decreased with further incubation, up to absence after 24 h. The difference in the antagonistic activity of 16-h-old and 24-h-old hours LAB cultures also was found. Among LAB tested, 241 strains are the most promising for further practical use, they have antagonistic action towards 10 indicator strains. The cross-streaking method can be used for rapid screening of bacteriocinogenic LAB strains and has advantages over the well-diffusion assay. To the best of our knowledge, this is the first report on a comparative characteristic of spectra of antagonistic activity against opportunistic pathogens of LAB strains belonging to different genera.

Antistaphylococcal and antioxidant activities of bacteriocinogenic lactic acid bacteria and essential oil in goat coalho cheese.

Bacteriocinogenic lactic acid bacteria (LAB) isolates and Croton heliotropiifolius essential oil (EO) were used to inhibit Staphylococcus aureus subsp. aureus and enhance the antioxidant action in goat coalho cheese (GCC). Lactic acid bacteria isolates were selected for their inhibitory capacity against S. aureus subsp. aureus, safety, existence of bacteriocin-encoding genes, bacteriocinogenic activity, and its antistaphylococcal action. The staphylococcal inhibition capacity of C. heliotropiifolius EO was also verified. Three cheeses were prepared containing S. aureus subsp. aureus (GCC SA), S. aureus subsp. aureus + LAB (GCC SA + LAB), and S. aureus subsp. aureus + EO (GCC SA + EO). Samples were analysed on days 0, 7, 14 and 21. Based on the screening, three LAB isolates were selected and identified as Enterococcus faecium. In GCC, the smallest population of S. aureus subsp. aureus was found until the 17th in the GCC SA + EO and from the 18th in the GCC SA + LAB. Total phenolic content and antioxidant activity increased over time in GCCs. Autochthonous bacteriocinogenic LAB and C. heliotropiifolius EO are natural resources of the Caatinga, an exclusively Brazilian biome that predominates in the northeast of the country, with the potential to reduce the presence of S. aureus and increase the antioxidant activity in the GCC. Goat coalho cheese is a product of cultural importance in northeastern Brazil. The process of obtaining the GCC is manual, and there is a high frequency of S. aureus in the product. Resources of the Caatinga with biofunctional properties can be tested to reduce the risk of staphylococcal toxins, and contribute to the nutritional value of the GCC, maintaining regional characteristics and respecting the local cultural tradition. LAB and C. heliotropiifolius EO contribute to the incorporation of bioactive substances and microbiological quality, generating a value-added GCC with exclusive resources of the Caatinga.

GENOTYPIC AND PHENOTYPIC CHARACTERIZATION OF BACTERIOCINOGENIC LACTIC ACID BACTERIAL STRAINS FOR POSSIBLE BENEFICIAL, VIRULENCE, AND ANTIBIOTIC RESISTANCE TRAITS

Lactic acid bacteria (LAB) are a diverse group of microorganisms that can be found in natural habitats and are used in a wide range of industries, especially in the food sector. They are regarded "Generally Recognized as Safe" and are commonly used as a starter culture, probiotics, and biopreservative. However, some LAB genera are excluded from the "Qualified Presumption of Safety" (QPS) list due to the possibility that they have virulence and antibiotic resistance genetic determinants. The objective of this study was to investigate the beneficial, virulence, and antibiotic resistance-related genes in 10 well-characterized bacteriocinogenic LAB strains. The auto-aggregation, co-aggregation, cell surface hydrophobicity, and bile salt tolerance were also evaluated to examine their potential as bacteriocinogenic probiotics and/or starter culture. Results showed that all tested strains showed abilities for auto-aggregation at 4oC and 37oC, co-aggregation with S. aureus JCM8704, S. typhimurium BIOTECH1826, and E. coli DH5α, and significant cell-surface hydrophobicity. However, only a few strains were able to withstand the media treated with 0.3% bile salt. Among the tested bacteriocinogenic LAB strains, L. lactis IO-1 and C. divergens V41 had the maximum values for auto-aggregation at 4oC and 37oC, respectively. C. divergens V41 also exhibited the highest percentage for cell surface hydrophobicity. E. faecium NKR-5-3 showed the highest co-aggregation percentages with all indicator strains. Our findings also showed that the tested isolates presented distinct combinations of virulence-related genes. Only two of ten bacteriocinogenic LAB strains exhibited presence of multiple virulence genes. Lactococcus sp. QU12 was found to have a high frequency of beneficial and virulence genes, with 2 out of 7 genes present encoding beneficial factor and 11 out of 13 genes encoding virulence factor. Lactococcus sp. QU12 and L. lactis IO-1 were also positive for tetracycline resistance gene tetM and aminoglycoside resistance gene aphA-2, respectively, and transposon genes. Moreover, only a few LAB isolates tested positive for 2 out of 8 antibiotic resistance classes. Although few, the substantial danger of these genes being transferred and acquired cannot be overlooked as this could potentially cause serious health concerns in the future. These results suggest that despite the promising properties of bacteriocinogenic LAB, careful safety evaluation of these strains should be a prerequisite before using these in food systems.

Genomic and functional characterization of bacteriocinogenic lactic acid bacteria isolated from Boza, a traditional cereal-based beverage

Boza is a traditional low-alcohol fermented beverage from the Balkan Peninsula, frequently explored as a functional food product. The product is rich in Lactic Acid Bacteria (LAB) and some of them can produce bacteriocins. In this study, a sample of Boza from Belogratchik, Bulgaria, was analyzed for the presence of bacteriocinogenic LAB, and after analyses by RAPD-PCR, three representative isolates were characterized by genomic analyses, using whole genome sequencing. Isolates identified as Pediococcus pentosaceus ST75BZ and Pediococcus pentosaceus ST87BZ contained operons encoding for bacteriocins pediocin PA-1 and penocin A, while isolate identified as Pediococcus acidilactici ST31BZ contained only the operon for pediocin PA-1 and a CRISPR/Cas system for protection against bacteriophage infection. The antimicrobial activity of bacteriocins produced by the three isolates was inhibited by treatment of the cell-free supernatants with proteolytic enzymes. The produced bacteriocins inhibited the growth of Listeria monocytogenes, Enterococcus spp. and some Lactobacillus spp., among other tested species. The levels of bacteriocin production varied from 3200 to 12,800 AU/ml recorded against L. monocytogenes 104, 637 and 711, measured at 24 h of incubation at 37 °C. All bacteriocins remained active after incubation at pH 2.0–10.0. The activity mode of the studied bacteriocins was bactericidal, as determined against L. monocytogenes 104, 637 and 711. In addition, bactericidal activity was demonstrated using a cell leakage β-galactosidase assay, indicating a pore formation mechanism as a mode of action. The present study highlights the importance of combining genomic analyses and traditional microbiological approaches as way of characterizing microbial interactions in fermented foods.

GENOTYPIC AND PHENOTYPIC CHARACTERIZATION OF BACTERIOCINOGENIC LACTIC ACID BACTERIAL STRAINS FOR POSSIBLE BENEFICIAL, VIRULENCE, AND ANTIBIOTIC RESISTANCE TRAITS

Lactic acid bacteria (LAB) are a diverse group of microorganisms that can be found in natural habitats and are used in a wide range of industries, especially in the food sector. They are regarded Generally Recognized as Safe and are commonly used as a starter culture, probiotics, and biopreservative. However, some LAB genera are excluded from the Qualified Presumption of Safety (QPS) list due to the possibility that they have virulence and antibiotic resistance genetic determinants. The objective of this study was to investigate the beneficial, virulence, and antibiotic resistance-related genes in 10 well-characterized bacteriocinogenic LAB strains. The auto-aggregation, co-aggregation, cell surface hydrophobicity, and bile salt tolerance were also evaluated to examine their potential as bacteriocinogenic probiotics and/or starter culture. Results showed that all tested strains showed abilities for auto-aggregation at 4oC and 37oC, co-aggregation with S. aureus JCM8704, S. typhimurium BIOTECH1826, and E. coli DH5α, and significant cell-surface hydrophobicity. However, only a few strains were able to withstand the media treated with 0.3% bile salt. Among the tested bacteriocinogenic LAB strains, L. lactis IO-1 and C. divergens V41 had the maximum values for auto-aggregation at 4oC and 37oC, respectively. C. divergens V41 also exhibited the highest percentage for cell surface hydrophobicity. E. faecium NKR-5-3 showed the highest co-aggregation percentages with all indicator strains. Our findings also showed that the tested isolates presented distinct combinations of virulence-related genes. Only two of ten bacteriocinogenic LAB strains exhibited presence of multiple virulence genes. Lactococcus sp. QU12 was found to have a high frequency of beneficial and virulence genes, with 2 out of 7 genes present encoding beneficial factor and 11 out of 13 genes encoding virulence factor. Lactococcus sp. QU12 and L. lactis IO-1 were also positive for tetracycline resistance gene tetM and aminoglycoside resistance gene aphA-2, respectively, and transposon genes. Moreover, only a few LAB isolates tested positive for 2 out of 8 antibiotic resistance classes. Although few, the substantial danger of these genes being transferred and acquired cannot be overlooked as this could potentially cause serious health concerns in the future. These results suggest that despite the promising properties of bacteriocinogenic LAB, careful safety evaluation of these strains should be a prerequisite before using these in food systems.

Combined antimicrobial effect of bacteriocins of LAB isolated from a traditional brine table olives and essential oils against foodborne pathogens

The study aimed to determine the antimicrobial activity of bacteriocinogenic lactic acid bacteria isolated from olive brine and three essential oils (Thyme, Rosemary and Oregano Eos) alone and in combination against the Gram-positive L. monocytogenes and the Gram-negative E. coli O157: H7. The antimicrobial activity was determined by evaluation of minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of the tested antimicrobial agents. The evaluation demonstrates that the two CFSs of lactic strains and the purified bacteriocins inhibit the growth of both L. monocytogenes and E. coli . The results showed that thyme EO is most effective followed by rosemary and Oregano Eos. Thus, all combination executed against L. monocytogenes using the checkerboard technique showed an additive effect unless the CFSs of LAB in combination with Thyme EO which showed no interactive effect. Whereas the combination against E. coli, only two bacteriocins in combination with Thyme EO and ELBC02 bacteriocin in combination with Rosemary EO that showed an additive effect. The results obtained in these studies coupled with the right knowledge opens the way to the combination as a new field of application whose goal is confined to conservation and the safety of food.

Characterization of Enterococcus faecium EO1 isolated from mutton and activity of bacteriocin-like substances in the control of Listeria monocytogenes in fresh mutton sausage

The aim of this study was to isolate and characterize bacteriocinogenic lactic acid bacteria (LAB) from mutton carcasses after slaughter. The study also evaluated the activity of bacteriocin-like substances (BLS) for control of Listeria monocytogenes in fresh mutton sausage. The cell-free supernatant (CFS) was obtained and its antimicrobial activity was quantified. The presence of genes encoding enterocin was evaluated by molecular techniques. Another aspect assessed was the action in situ of BLS produced by these isolates for control of Listeria monocytogenes in fresh mutton sausage, experimentally contaminated. Six isolates presented phenotypic and genotypic characteristics of safety. Also, the antibacterial peptides present in the CFS showed stability at different temperatures, pH, NaCl and cure salt concentrations, as well as potential against L. monocytogenes Scott A. The isolate identified as Enterococcus faecium EO1 showed gene coding for the production of enterocin A and produced bacteriocin after 6 h of growth (400 AU. mL−1). Based on this, the CFS of EO1 (5 and 10%) was applied in fresh mutton sausage, being significantly effective for control of L. monocytogenes during 21 days of refrigerated storage (4.07 log CFU. g−1). Therefore, the potential for preservation of food has been demonstrated through the use of CFS containing bacteriocin-like substances from E. faecium EO1 in fresh mutton sausage.

Effectiveness of Bacteriocin-Producing Lactic Acid Bacteria and Bifidobacterium Isolated from Honeycombs against Spoilage Microorganisms and Pathogens Isolated from Fruits and Vegetables

Screening natural products for bacteriocin-producing bacteria may be the equilibrium point between the consumer demand for mild processing and the industry’s need for hazard control. Raw unprocessed honeycombs filled with oregano honey from the alpine mountainous territory of Epirus, Greece were screened for bacteriocinogenic lactic acid bacteria and Bifidobacterium spp., with inhibitory action towards some pathogens and spoilage microorganisms isolated from fresh fruits and vegetables (number and type of strains: three E. coli, two L. monocytogenes, two Salmonella spp., two B.cereus, two Erwinia spp., one Xanthomonas spp., L. innocua (ATCC 33090TM) and E. coli 0157:H7 (ATCC 69373)). Among the 101 collected isolates (73 Lactobacillus, 8 Lactococcus, 8 Leuconostoc and 12 Bifidobacterium species) from the oregano honeycombs (an original finding since there are no other reports on the microbial biodiversity of the flora of the oregano honey), 49 strains of lactic acid bacteria (LAB) and Bifidobacterium spp. were selected and tested for their bacteriocin-producing capacity (34 Lactobacillus, 6 Lactococcus, 5 Leuconostoc and 4 Bifidobacterium). The antibacterial activity exerted by the tested LAB and Bifidobacterium strains was not of the same potency. Our results suggest that the main molecules involved in the antimicrobial activity are probably bacteriocin-like substances (a conclusion based on reduced antibacterial activity after the proteolytic treatment of the cell-free supernatant of the cultures) and this antimicrobial activity is specific for the producing strains as well as for the target strains. The spoilage bacteria as well as the reference microorganisms showed increased resistance to the bacteriocin-like substances in comparison to the wild-type pathogens.

Molecular identification and antibiotic resistance of bacteriocinogenic lactic acid bacteria isolated from table olives.

In the present study, lactic acid bacteria were isolated from table olive in Morocco. Random Amplified Polymorphic DNA fingerprinting with (GTG)'(5) primer revealed a remarquable variability within isolates. According to the molecular identification, Enterococcus faecium was the most dominant species isolated with 32 strains (84.21%), followed by 4 strains of Weissella paramesenteroides (10.52%), 1 strain of Leuconostoc mesenteroides (2.63%) and Lactobacillus plantarum (2.63%). All of the strains that were identified showed occurrence of more than one bacteriocin-encoding gene. Based on the results obtained, L. plantarum 11 showed a mosaic of loci coding for nine bacteriocins (pln A, pln D, pln K, pln G, pln B, pln C, pln N, pln J, ent P). A phenotypic and genotypic antibiotic resistance was also examined. L. plantarum 11, L. mesenteroides 62, W. paramesenteroides 9 and W. paramesenteroides 36 as well as all the strains of E. faecium were susceptible to ampicillin, clindamycin and teicoplanin; however, isolates showed a resistance profile against tetracycline and erythromycin. Except E. faecium 114, E. faecium 130 and L. plantarum 11, no antibiotic resistance genes were detected in all of the strains, which might be due to resistances resulting from non-transferable or non-acquired resistance determinants (intrinsic mechanism).

Process parameters optimization and molecular studies on bacteriocin-producing lactic acid bacteria from ‘Kati’

This work described the isolation and identification of bacteriocin-producing lactic acid bacteria (LAB) from ‘Kati’(a sorghum based fermented food), and to evaluate the antibacterial effect of bacteriocin on selected pathogenic bacteria. The identities of the isolates were revealed to be as Lactobacillus plantarum, L. brevis, L. fermentum KAT1, L. fermentum KAT2 and Lactococcus lactis using 16S rRNA gene sequence analysis. Out of 28 LAB, five were found to inhibit selected pathogenic bacteria namely; Escherichia coli, Staphylococcus aureus, Salmonella typhimurium and Bacillus cereus. The unpurified bacteriocins produced by the isolated LAB were characterized with respect to the effect of temperature, pH and surfactant. The test isolates showed activities of 6400, 6400, 6400, 3200 and 1600 AU/ml respectively. Crude bacteriocin from L. brevis and L. lactis were the most heat stable at 121ºC for 60 min. Bacteriocins from L. plantarum, L. lactis and L. fermentum KAT1 showed the highest antibacterial activity and stability at pH 2.0 to 6.0. Exposure to Tween 20 increased the bacteriocin activity of the LAB isolates except for L. fermentum KAT2 where loss of activity occurred. The findings from this study suggest that bacteriocinogenic LAB present in ‘kati’ have potentials to inhibit pathogenic/spoilage microorganisms in foods.

In situ Listeria monocytogenes biocontrol and sensory attributes enhancement in raw beef meat by Enterococcus lactis

The enterocin P-producing Enterococcus lactis strain Q1 was directly added at 107 CFU/g in refrigerated raw beef to evaluate its effectiveness in the control of Listeria monocytogenes EGDe 107776 proliferation. Furthermore, sensorial evaluation of the quality of treated beef meat samples with the enterococcal protective culture was performed basing on color, odor, and appearance parameters for 14 days. As a result, it was demonstrated that the enterocin P-producing E. lactis Q1 strain led to a remarkable reduction (p < .05) of L. monocytogenes in beef meat by 6.47 ± 0.30 log units after 7 days and 7.25 ± 0.35 log units below the control after 14 days, then remained stable up to 28 days of cold storage. Also, E. lactis Q1 strain improved significantly (p < .05) the organoleptic quality of treated beef sample. Hence, E. lactis Q1 clearly indicates its efficiency to be used as protective agent in a wide range of meat products. Practical applications Preserving meat using new bacteriocinogenic lactic acid bacteria is an important agenda to ensure consumer safety. The present study showed the ability of an enterocin P-producing strain named E. lactis Q1, added in raw beef meat during cold storage, to inhibit L. monocytogenes and improve meat sensory properties. Hence, E. lactis Q1 can be used in the future to develop healthy meat products with better shelf life and quality.

Characterization of purified antimicrobial peptide produced by Pediococcus pentosaceus LJR1, and its application in preservation of white leg shrimp.

The bacteriocinogenic lactic acid bacterium Pediococcus pentosaceus LJR1 isolated from rumen liquor of goat had strong anti-bacterial activity toward Listeria monocytogenes in vitro. This antibacterial activity was lost on treatment with protease indicating that the bacteriocin is proteinaceous in nature. The bacteriocin LJR1 produced by P. pentosaceus was purified following a three step procedure consisting of ammonium sulphate precipitation, gel filtration chromatography and reverse phase-high performance liquid chromatography. The molecular weight of purified bacteriocin was determined to be 4.6kDa using Tricine SDS-PAGE. Further, we found that the proteinaceous bacteriocin was stable at 100°C as well as 121°C for 30min and 15min respectively and also at different pH ranging from 4 to 10 when stored for 15min at 37°C. Its minimum inhibitory concentration for S. typhi MTCC134 and L. monocytogenes MTCC 1143 was 7.81µg/ml and 15.63µg/ml respectively. Scanning electron microscopy analysis of the surface of S. typhi treated with the bacteriocin showed the presence of craters; while in the case of treated L. monocytogenes blebs were observed. The addition of the bacteriocin to shrimp (white leg shrimp) has led to reduction of about 1 log units of L. monocytogenes on day 1 and maintained for 7days on storage at 4°C. It is clear that the purified bacteriocin has good potential as a bio preservative for application in food industry.

BACTERIOCINOGENIC POTENTIAL OF LACTIC ACID BACTERIA ISOLATED FROM ARTISANAL COLONIAL TYPE - CHEESE

Autochthonous microbiota from artisanal cheeses is predominantly composed of lactic acid bacteria (LAB), which are able to produce antimicrobial compounds, such as bacteriocins, suggesting their application in food biopreservation. Knowledge about LAB growth and bacteriocin production during food production and conservation is essential to determine their use. In this way, the study aimed at isolating bacteriocinogenic LAB from twenty-one artisanal cheeses from the western region of Parana state, Brazil, determining the best conditions for growth and bacteriocin production (25°C, 30°C, and 37°C/24h); bacteriocin stability under different ranges of pH (2, 4, 6, 8, and 10 for 2h) and temperature (60oC/2h; 80oC/2h; 121oC/15min). Their activity against different target microorganisms was also evaluated. A total of 34 LAB strains presented characteristics compatible with bacteriocin production. Most of them presented better results for bacteriocin production when cultured at 25ºC and 30ºC. Bacteriocins remained active against L. monocytogenes when exposed from pH 4 to 8 and a wide temperature range; some bacteriocins were even resistant to sterilization temperatures. Bacteriocins produced were able to inhibit spoilage and pathogenic microorganisms, such as L. monocytogenes, B. cereus, and P. fluorescens. These results indicated that isolated bacteriocinogenic LAB present potential to be used as food biopreservatives.

Biochemical, genetic and transcriptional characterization of multibacteriocin production by the anti-pneumococcal dairy strain Streptococcus infantariusLP90.

Streptococcus pneumoniae infections are one of the major causes of morbility and mortality worldwide. Although vaccination and antibiotherapy constitute fundamental and complementary strategies against pneumococcal infections, they present some limitations including the increase in non-vaccine serotypes and the emergence of multidrug-resistances, respectively. Ribosomally-synthesized antimicrobial peptides (i.e. bacteriocins) produced by Lactic Acid Bacteria (LAB) may represent an alternative or complementary strategy to antibiotics for the control of pneumococal infections. We tested the antimicrobial activity of 37 bacteriocinogenic LAB, isolated from food and other sources, against clinical S. pneumoniae strains. Streptococcus infantarius subsp. infantarius LP90, isolated from Venezuelan water-buffalo milk, was selected because of its broad and strong anti-pneumococcal spectrum. The in vitro safety assessment of S. infantarius LP90 revealed that it may be considered avirulent. The analysis of a 19,539-bp cluster showed the presence of 29 putative open reading frames (ORFs), including the genes encoding 8 new class II-bacteriocins, as well as the proteins involved in their secretion, immunity and regulation. Transcriptional analyses evidenced that the induction factor (IF) structural gene, the bacteriocin/IF transporter genes, the bacteriocin structural genes and most of the bacteriocin immunity genes were transcribed. MALDI-TOF analyses of peptides purified using different multichromatographic procedures revealed that the dairy strain S. infantarius LP90 produces at least 6 bacteriocins, including infantaricin A1, a novel anti-pneumococcal two-peptide bacteriocin.