Antibacterial activity of some lactic acid bacteria isolated from an Algerian dairy product

Bio-Preservation Potential and Antimicrobial Activity of Bacteriocin-Producing Lactic Acid Bacteria Isolated from Ethiopian Traditional Fermented Dairy Products

This study aimed to assess the antibacterial activity and bio-preservation capability of bacteriocin-producing LAB isolated from Ethiopian traditional fermented dairy products in raw milk from Jimma town. Bacteriocin-producing LAB were tested for their antimicrobial activity against various foodborne pathogens, including Staphylococcus aureus, Escherichia coli, Listeria monocytogenes, and Salmonella typhimurium. The results showed that probiotic LAB isolates inhibited foodborne pathogens (E. coli, S. aureus, and L. monocytogenes), with inhibition zones ranging from 22.00 ± 0.57 to 34.13 ± 0.57. Enterococcus faecium and Lactococcus lactis demonstrated possible antagonistic effects against E. coli, while Pediococcus pentosaceus had a 34.13 ± 0.57 mm inhibitory zone against Pseudomonas aeruginosa. The isolates also showed co-aggregation potential with the pathogens, with Lactococcus lactis isolates and their combinations demonstrating the best co-aggregation capabilities against the investigated pathogens. The bio-preservative assay showed that putative probiotic isolates (L. lactis JULABE35, E. faecium JULABE 23, and P. pentosaceus JULABE05) were efficient in decreasing Listeria monocytogenes in raw milk. After 7-8 days, milk samples diagnosed with these isolates showed complete reduction of Listeria monocytogenes. The bio-preservation capability of bacteriocin-producing LAB on raw milk extended the shelf life of milk at 4 °C storage for ten days, compared to six days for milk samples without probiotic LAB. The milk samples preserved with probiotic and bacteriocin-producing isolates showed good proximate analysis, showing significant variation with milk kept without bacteriocin-producing isolates. The isolated chemicals employed in this study can be used as food additives or food preservatives, indicating potential applications in Ethiopian traditional fermented dairy products.

Putative Role of Anti-microbial Peptide Recovered from Lactiplantibacillus spp. in Biocontrol Activity

Antimicrobial peptides (AMPs) stand as a promising alternative to conventional pesticides, leveraging a multifaceted approach to combat plant pathogens. This study focuses on identifying and characterizing the AMP produced by Lactiplantibacillus argentoratensis strain IT, demonstrating potent antibacterial activity against various harmful microorganisms. Evaluation of AMPs' antibacterial activity was conducted through an agar well diffusion assay, a reliable method for assessing secondary metabolite antimicrobial efficacy. The study unveils the antimicrobial potential of the purified extract obtained from Lactiplantibacillus argentoratensis IT, isolated from goat milk. Notably, the AMP exhibited robust antibacterial activity against phytopathogens affecting solanaceous crops, including the Gram-negative Ralstonia solanacearum. Expression conditions and purification methods were optimized to identify the peptide's mass and sequence, utilizing LC-MS and SDS-PAGE. This paper underscores the application potential of Lactiplantibacillus spp. IT as a biocontrol agent for managing bacterial infectious diseases in plants. Results indicate optimal AMP production at 37 °C, with a culture broth pH of 5 during fermentation. The obtained peptide sequence corresponded to peaks at 842.5 and 2866.4 m/z ratio, with a molecular weight of approximately 5 kDa according to tricine SDS-PAGE analysis. In conclusion, this study lays the foundation for utilizing Lactiplantibacillus spp. IT derived AMPs in plant biocontrol strategies, showcasing their efficacy against bacterial phytopathogens. These findings contribute valuable insights for advancing sustainable agricultural practices.

B. C, Huligere SS, Khan MS, Alafaleq NO, Ahmad S, Akhter F, Sreepathi N, P. A, Ramu R. Inhibition of carbohydrate hydrolyzing enzymes by a potential probiotic Levilactobacillus brevis RAMULAB49 isolated from fermented Ananas comosus

The research aimed to explore the potential probiotic characteristics of Levilactobacillus brevis RAMULAB49, a strain of lactic acid bacteria (LAB) isolated from fermented pineapple, specifically focusing on its antidiabetic effects. The importance of probiotics in maintaining a balanced gut microbiota and supporting human physiology and metabolism motivated this research. All collected isolates underwent microscopic and biochemical screenings, and those exhibiting Gram-positive characteristics, negative catalase activity, phenol tolerance, gastrointestinal conditions, and adhesion capabilities were selected. Antibiotic susceptibility was assessed, along with safety evaluations encompassing hemolytic and DNase enzyme activity tests. The isolate's antioxidant activity and its ability to inhibit carbohydrate hydrolyzing enzymes were examined. Additionally, organic acid profiling (LC-MS) and in silico studies were conducted on the tested extracts. Levilactobacillus brevis RAMULAB49 demonstrated desired characteristics such as Gram-positive, negative catalase activity, phenol tolerance, gastrointestinal conditions, hydrophobicity (65.71%), and autoaggregation (77.76%). Coaggregation activity against Micrococcus luteus, Pseudomonas aeruginosa, and Salmonella enterica serovar Typhimurium was observed. Molecular characterization revealed significant antioxidant activity in Levilactobacillus brevis RAMULAB49, with ABTS and DPPH inhibition rates of 74.85% and 60.51%, respectively, at a bacterial cell concentration of 109 CFU/mL. The cell-free supernatant exhibited substantial inhibition of α-amylase (56.19%) and α-glucosidase (55.69%) in vitro. In silico studies supported these findings, highlighting the inhibitory effects of specific organic acids such as citric acid, hydroxycitric acid, and malic acid, which displayed higher Pa values compared to other compounds. These outcomes underscore the promising antidiabetic potential of Levilactobacillus brevis RAMULAB49, isolated from fermented pineapple. Its probiotic properties, including antimicrobial activity, autoaggregation, and gastrointestinal conditions, contribute to its potential therapeutic application. The inhibitory effects on α-amylase and α-glucosidase activities further support its anti-diabetic properties. In silico analysis identified specific organic acids that may contribute to the observed antidiabetic effects. Levilactobacillus brevis RAMULAB49, as a probiotic isolate derived from fermented pineapple, holds promise as an agent for managing diabetes. Further investigations should focus on evaluating its efficacy and safety in vivo to consider its potential therapeutic application in diabetes management.

Comprehensive study upon physicochemical properties of bio-ZnO NCs

In this study, for the first time, the comparison of commercially available chemical ZnO NCs and bio-ZnO NCs produced extracellularly by two different probiotic isolates (Latilactobacillus curvatus MEVP1 [OM736187] and Limosilactobacillus fermentum MEVP2 [OM736188]) were performed. All types of ZnO formulations were characterized by comprehensive interdisciplinary approach including various instrumental techniques in order to obtain nanocomposites with suitable properties for further applications, i.e. biomedical. Based on the X- ray diffraction analysis results, all tested nanoparticles exhibited the wurtzite structure with an average crystalline size distribution of 21.1 nm (CHEM_ZnO NCs), 13.2 nm (1C_ZnO NCs) and 12.9 nm (4a_ZnO NCs). The microscopy approach with use of broad range of detectors (SE, BF, HAADF) revealed the core-shell structure of bio-ZnO NCs, compared to the chemical one. The nanoparticles core of 1C and 4a_ZnO NCs are coated by the specific organic deposit coming from the metabolites produced by two probiotic strains, L. fermentum and L. curvatus. Vibrational infrared spectroscopy, photoluminescence (PL) and mass spectrometry (LDI-TOF-MS) have been used to monitor the ZnO NCs surface chemistry and allowed for better description of bio-NCs organic coating composition (amino acids residues). The characterized ZnO formulations were then assessed for their photocatalytic properties against methylene blue (MB). Both types of bio-ZnO NCs exhibited good photocatalytic activity, however, the effect of CHEM_ZnO NCs was more potent than bio-ZnO NCs. Finally, the colloidal stability of the tested nanoparticles were investigated based on the zeta potential (ZP) and hydrodynamic diameter measurements in dependence of the nanocomposites concentration and investigation time. During the biosynthesis of nano-ZnO, the increment of pH from 5.7 to around 8 were observed which suggested possible contribution of zinc aquacomplexes and carboxyl-rich compounds resulted in conversion of zinc tetrahydroxy ion complex to ZnO NCs. Overall results in present study suggest that used accessible source such us probiotic strains, L. fermentum and L. curvatus, for extracellular bio-ZnO NCs synthesis are of high interest. What is important, no significant differences between organic deposit (e.g. metabolites) produced by tested strains were noticed-both of them allowed to form the nanoparticles with natural origin coating. In comparison to chemical ZnO NCs, those synthetized via microbiological route are promising material with further biological potential once have shown high stability during 7 days.

Isolation and Characterization of Lactic Acid Bacteria from Fermented Milk Produced in Jimma Town, Southwest Ethiopia, and Evaluation of their Antimicrobial Activity against Selected Pathogenic Bacteria

Background

Raw milk is usually contaminated with pathogenic bacteria. Fermentation of milk is important to inhibit the growth of contaminants, spoilage, and pathogenic bacteria. The objective of this study was to isolate lactic acid bacteria from fermented milk and evaluate their antimicrobial activity against selected pathogenic bacteria.

Methods

Laboratory-based experimental study design was conducted from May-July, 2021.Three samples of Ergo (each of 250 ml) were collected from Jimma town. Lactic acid bacteria (LAB) isolates were identified through integrated phenotypic techniques. Further identification was conducted through using API 50 CHL strips. Antimicrobial activities (AMAs) of LAB isolates were tested against clinical isolates of E. coli, S. aureus, and Salmonella spp. using agar well diffusion method. The data were analyzed by using SPSS software version 21 and Microsoft Excel spreadsheet. Tables and figures were applied to describe characteristics of data.

Results

Twelve LAB isolates were identified. Those LAB isolates include six Lactococcus lactis subsp. lactis, Lactobacillus acidophilus (2), Lactiplantibacillus plantarum (1), Limosilactobacillus fermentum (2), and Leuconostoc lactis (1). Based on primary screening of LAB, isolates/strains ESCIa, ESBIa, and ESCIc show strong AMA against S. aureus, E. coli, and Salmonella spp. The CFS of ESCIc showed the highest AMA against S. aureus and Salmonella spp. with a zone of inhibition of 14.12 ± 1.6 mm and 12.9 ± 3.6 mm, respectively, while ESBIa showed the highest AMA against E. coli with a zone of inhibition of 13.5 ± 2.1 mm. The CFSs of selected LAB strains were heat tolerant at varying temperatures up to 100°C. The CFSs of selected LAB strains were inactivated by proteinase enzymes, but they are not inactivated with amylase enzymes. Conclusions and Recommendation. All 12 LAB isolates exhibited antimicrobial activity against tested bacterial strains. Lactobacillus isolates showed the highest antagonistic activity on tested indicator strains. Thus, they are possible alternatives to antibiotics in the era of antimicrobial resistance. S. aureus was the most sensitive to antimicrobial effects/agents of selected LAB isolates. Consumption of fermented foods is advisable since they support the growth of healthy GIT microbiota. Fermentation serves as biopreservation of food. However, analysis of probiotic features and in vivo probiotic effects of those LAB isolates will be subject of future research/study.

Probiotic bacteria from 10 different traditional Iranian cheeses: Isolation, characterization, and investigation of probiotic potential

In this study, 10 different traditional Iranian cheeses, which are still consumed by people in rural areas of Iran, were examined to isolate new strains of probiotic bacteria. Isolated bacteria were identified by 16s rRNA gene amplification and subjected to series of in vitro tests to find out their probiotic potential. A total of 2345 colonies were collected and 465 of them were confirmed as lactic acid bacteria (LAB), of which Lactiplantibacillus plantarum, Lactobacillus bulgaricus, and Lacticaseibacillus casei were the top three isolated bacteria. Among the different species of LAB isolated in this study, Lactip. plantarum was the most isolated species, and seven isolates had the significant criteria for being a probiotic strain than other isolates indicating the most adaptable properties of this species. Lactiplantibacillus plantarum was the most resistant bacteria in the bile resistance test and was also the most durable bacteria in gastrointestinal conditions, for example, acidic environment (pH = 2.5) and trypsin. In contrast, Lacticaseibacillus casei was the most susceptible bacterial strain. Lactobacillus rhamnosus showed the most antibacterial effect against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. This study showed that probiotic strains isolated from local cheeses could be considered as suitable biopreservatives and used as specific starter cultures for the production of functional cheeses.

Antagonistic Effects of Conjugated Linoleic Acids of Lactobacillus casei against Foodborne Enterohemorrhagic Escherichia coli

ABSTRACT

Probiotics in fermented foods or commercially available supplements benefit the host by providing metabolites and peptides. The production of these metabolites varies with the available substrates or prebiotics present in the system and their concentration. In this study, 0.5% peanut flour (PF) was used to stimulate the growth and production of metabolites of wild-type Lactobacillus casei (LCwt) and compare with an engineered L. casei (LCCLA) capable of converting a higher amount of conjugated linoleic acid (CLA). The total extracellular metabolites present in the cell-free cultural supernatant (CFCS) of LCwt (without peanut), LCwt+PF (with peanut), and LCCLA were collected after 24 and 48 h of incubation, and their antagonistic activities against enterohemorrhagic Escherichia coli (EHEC EDL933) growth and pathogenesis were evaluated. All collected metabolites exhibited varying efficiency in restraining EHEC EDL933 growth, whereas supplementing a low concentration of CLA to the 48-h CFCS from LCwt showed augmented antagonism toward EHEC EDL933. A downregulation of key virulence genes was observed from metabolites collected at the 48-h time point. These observations indicate that the presence of metabolites in CFCSs-including CLA, which is produced by Lactobacillus and was identified by gas chromatography-mass spectrometry-plays a critical role. This study demonstrates the potential applicability of Lactobacillus-originated CLA in the prevention of EHEC EDL933-mediated illnesses.

HIGHLIGHTS

Study on the applicability of potentially probiotic strain Lactobacillus plantarum L4 to be included in the development of strategies for bio-preservation of food products

The antimicrobial activity of potentially probiotic strains is important for their possible application in the development of successful strategies for bio-preservation of different foods. The antimicrobial activity of the potentially probiotic strain Lactobacillus plantarum L4 against the pathogenic bacteria Salmonella abony; Staphylococcus aureus; Escherichia coli and the phytopathogenic fungi Aspergillus niger and Aspergillus flavus was determined using agar-diffusion assay with wells. Lb. plantarum L4 exhibited high antagonistic activity against all test microorganisms included in the study, which was due not only to the production and accumulation of lactic acid and other organic acids, but also to the production of other bioactive substances. The bioactive substances were then submitted to the action of different enzymes. This allowed to observe that they have protein nature, suggesting that they are likely bacteriocins or bacteriocin-like substances. The substances produced by Lb. plantarum L4 did not lose their antimicrobial activity during heat treatment at temperatures above 100 °С for 15 min and they exhibited high inhibitory activity against the test-microorganisms when pH ranged between 4 and 7. After further examination of the properties of the produced antimicrobial compounds, Lb. plantarum L4 can be used in the development of strategies for bio-preservation of different food products.

Antagonistic Mechanism of Metabolites Produced by Lactobacillus casei on Lysis of Enterohemorrhagic Escherichia coli

Enhancing extracellular metabolic byproducts of probiotics is one of the promising strategies to improve overall host health as well as to control enteric infections caused by various foodborne pathogens. However, the underlying mechanism of action of those metabolites and their effective concentrations are yet to be established. In this study, we determined the antibacterial potential of the metabolites in the cell-free culture supernatant (CFCS) collected from wild-type Lactobacillus casei (LC_wt) and genetically modified LC to overexpress linoleate isomerase (LC_CLA). We also evaluated the mechanism of action of CFCSs collected from the culture of LC_wt in the presence or absence of 0.5% peanut flour (CFCS^wt and CFCS^wt+PF, respectively) and LC_CLA alone (CFCS^CLA) against enterohemorrhagic Escherichia coli (EHEC). The metabolites present in CFCS^wt+PF and CFCS^CLA eliminated EHEC within 24 and 48 h, respectively. Whereas CFCS^wt failed to eliminate EHEC but reduced their growth by 6.7 logs (p < 0.05) as compared to the control. Significant downregulation of the expression of cell division gene, ftsZ, supported the observed degree of bactericidal and bacteriostatic properties of the collected CFCSs. Upregulation of EHEC genes related to maintaining cell membrane integrity, DNA damage repair, and molecular chaperons indicated an intensive stress condition imposed by the total metabolites present in CFCSs on EHEC growth and cellular structures. A range of deviated morphological features provoked by the metabolites indicated a membrane-targeted action, in general, to compromise the membrane permeability of EHEC. The information obtained from this study may contribute to a more efficient prevention of EHEC related infections.

Preliminary studies on the inhibition potential of Indian domestic curd against coliforms, an emerging periodontal pathogen

Background:

Coliforms colonize in dental plaques via oral route and may lead to systemic complications. Escherichia coli and its lipopolysaccharide-induced periodontitis is an emerging threat. Clinical management necessitates antibiotic regimens with risk of resistance and upsetting the gut. There is urgent need for better, sustainable, and economical alternative.

Aim:

To investigate the inhibition of coliforms, a potential periodontopathogen directly by Indian domestic curd (IDC) “in situ".

Materials and Methods:

Coliforms from natural habitat (Municipal sewage in Agartala, Tripura), a source of infection through food and water, were used as target organism. Domestically prepared curd without any fortification is used to explore its true inhibition potential. Assays of agar well diffusion performed with IDC (ultraviolet sterilized and pH adjusted 6.5) against isolated pure cultures of coliforms. The study protocol nullified effect of organic acids, volatile compounds, bacteriophages, and peroxides in IDC. Peptide nature of inhibitory ingredient was studied by Sodium Dodecyle Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE), urea treatment. Computational phylogenetics revealed structural features of inhibitory ingredient. Statistical comparisons were done by analysis of variance. Second-order polynomial regression was done to evaluate the effect of IDC dilution on coliform inhibition. Mann–Whitney U-test performed to analyze different sample treatments.

Results:

Agar well diffusion (sealed bottom wells) shows inhibition of catalase-negative coliforms (confirmed by Gram staining and triple sugar iron agar assay) in pure culture (MacConkey agar). Activity diminished in urea, potentiated in ethylene diamine tetra acetic acid, remains unchanged by heat treatment (121°C, 15 min). SDS-PAGE revealed three distinct peptides (>10–15KDa). Hence, thermostable inhibitory peptides attached to target cell lead to observed activity (titer up to 1204.82 AU/ml with minimum 8 mm inhibition).

Conclusions:

IDC adequately inhibits sewage coliforms and may prevent dental plaques coliform colonization and its associated risks.

Comparative Growth Behaviour and Biofunctionality of Lactic Acid Bacteria During Fermentation of Soy Milk and Bovine Milk

The study reports the growth, acidification and proteolysis of eight selected lactic acid bacteria in skim and soy milk. Angiotensin-converting enzyme inhibition and antimicrobial profiles of skim and soy milk fermented by the lactic acid bacteria were also determined. Among eight lactic cultures (S. thermophilus MD2, L. helveticus V3, L. rhamnosus NS6, L. rhamnosus NS4, L. bulgaricus NCDC 09, L. acidophilus NCDC 15, L. acidophilus NCDC 298 and L. helveticus NCDC 292) studied, L. bulgaricus NCDC 09 and S. thermophilus MD2 decreased the pH of skim and soy milk in greater extent. Acid production (i.e. titratable acidity) by L. bulgaricus NCDC 09 and L. helveticus V3 was higher than other strains. Higher viable counts were observed in S. thermophilus MD2 and L. helveticus V3. Higher proteolysis was exhibited by S. thermophilus MD2 and L. rhamnosus NS6 in both skim and soy milk. Milk fermented by S. thermophilus (MD2) exhibited highest angiotensin-converting enzyme inhibition. Antimicrobial activities of cell-free supernatant of milk fermented by S. thermophilus MD2 and L. helveticus V3 were higher. All the tested lactic acid bacteria performed better in skim milk as compared to soy milk.

In Vitro Assessment of the Probiotic Potential of Lactococcus lactis LMG 7930 against Ruminant Mastitis-Causing Pathogens

Mastitis in dairy ruminants is considered to be the most expensive disease to farmers worldwide. Recently, the intramammary infusion of lactic acid bacteria has emerged as a potential new alternative to antibiotics for preventing and treating bovine mastitis. In this study we have investigated in vitro the probiotic potential of Lactococcus lactis LMG 7930, a food-grade and nisin-producing strain, against mastitis-causing pathogens. We have characterized its carbohydrate fermentation and antibiotic susceptibility profiles, cell surface properties and antimicrobial activity, as well as its capabilities to adhere to and inhibit the invasion of pathogens into the bovine mammary epithelial cell line BME-UV1d. We found that L. lactis LMG 7930 was sensitive to tested drugs, according to the EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP), and showed an improved carbohydrate fermentation capacity compared to starter strains. Moreover, the strain exhibited antagonistic properties towards many of the pathogens tested. It presented medium surface hydrophobicity, a low basic property and no electron acceptor capability. It showed low auto-aggregation and no co-aggregation abilities towards any of the tested pathogens. The strain was one of the most adhesive to bovine mammary epithelial cells among tested bacteria, but its internalisation was low. The strain did not affect significantly pathogen invasion; however, a trend to decrease internalization of some pathogens tested was observed. In conclusion, our results suggest that this strain might be a promising candidate for the development of new strategies of mastitis control in ruminants. Future investigations are needed to evaluate its safety and efficacy under field conditions.

Antimicrobial activity and partial characterization of bacteriocin-like inhibitory substances produced by Lactobacillus spp. isolated from artisanal Mexican cheese

Lactobacillus spp. from Mexican Cocido cheese were shown to produce bacteriocin-like substances (BLS) active against Staphylococcus aureus,Listeria innocua,Escherichia coli, andSalmonella typhimurium by using the disk diffusion method. Crude extracts of Lactobacillus fermentum showed strong inhibitory activity against Staph. aureus, L. innocua, E. coli, and Salmonella cholerae. Complete inactivation of antimicrobial activity was observed after treatment of crude extracts with proteinase K, pronase, papain, trypsin, and lysozyme, confirming their proteinaceous nature. However, antimicrobial activity was partly lost for some of the crude extracts when treated with α-amylase, indicating that carbohydrate moieties were involved. The antimicrobial activity of the crude extracts was stable at 65°C for 30min over a wide pH range (2-8), and addition of potassium chloride, sodium citrate, ethanol, and butanol did not affect antibacterial activity. However, antimicrobial activity was lost after heating at 121°C for 15min, addition of methanol or Tween 80. Fourteen out of 18 Lactobacillus spp. showed antimicrobial activity against different test microorganisms, and 12 presented bacteriocin-like substances. Generation time and growth rate parameters indicated that the antimicrobial activity of crude extracts from 3 different strains was effective against the 4 indicator microorganisms. One of the crude extracts showed inhibition not only against gram-positive but also against gram-negative bacteria. Bacteriocin-like substances produced by this specific Lactobacillus strain showed potential for application as a food biopreservative.

Impact of exopolysaccharide production on functional properties of some Lactobacillus salivarius strains

The aim of this work was to characterize functional properties of Lactobacillus salivarius strains isolated from chicken feces. Detection of genes responsible for exopolysaccharide (EPS) production revealed that all strains harbored a dextransucrase gene, but p-gtf gene was only detected in strain E4. Analysis of EPS production levels showed significant alterations among strains tested. Biofilm formation was found to be medium composition dependant, and there was a negative correlation with biofilm formation and EPS production. Autoaggregation properties and coaggregation of L. salivarius strains with chicken pathogens were appeared to be specific at strain level. An increment in bacterial adhesion to chicken gut explants was observed in L. salivarius strains with the reduction in EPS production levels. This study showed that strain-specific properties can determine the functional properties of L. salivarius strains, and the interference of these properties might be crucial for final selection of these strains for technological purposes.

Bacteriocin from Bacillus subtilis as a novel drug against diabetic foot ulcer bacterial pathogens

OBJECTIVE

To isolate and identify Bacillus subtilis (B. subtilis) from soil and to characterize and partially purify the bacteriocin. To evaluate the antimicrobial activity against four diabetic foot ulcer bacterial pathogens.

METHODS

Genotypic identification was done based on Bergey's manual of systemic bacteriology. Antimicrobial susceptibility test was done by Kirby-Bauer disc diffusion method. Colonies were identified by colony morphology and biochemical characterization and also compared with MTCC 121 strain. Further identification was done by 16S rRNA sequencing. Inhibitory activities of partially purified bacteriocin on all the DFU isolates were done by agar well diffusion method. The strain was identified to produce bacteriocin by stab overlay assay. Bacteriocin was extracted by organic solvent extraction using chloroform, further purified by HPLC and physical, and chemical characterization was performed.

RESULTS

The four isolates showed high level of resistance to amoxyclav and sensitivity to ciprofloxacin. HPLC purification revealed that the extracts are bacteriocin. The phylogenetic tree analysis results showed that the isolate was 99% related to B. subtilis BSF01. The results reveled activity to all the four isolates and high level of activity was seen in case of Klebsiella sp.

CONCLUSIONS

Partially purified bacteriocin was found to have antimicrobial activity against the four diabetic foot ulcer bacterial pathogens, which can thus be applied as a better drug molecule on further studies. The strain B. subtilis are found to be safe for use and these antimicrobial peptides can be used as an antimicrobial in humans to treat DFU bacterial pathogens.

Cyclic dipeptides from lactic acid bacteria inhibit proliferation of the influenza A virus

We isolated Lactobacillus plantarum LBP-K10 from the traditional Korean fermented food kimchi. When organic acids were removed, the culture filtrate of this isolate showed high antiviral activity (measured using a plaque-forming assay) against the influenza A (H3N2) virus. Two fractions that were active against influenza A virus were purified from the culture filtrate using a C18 column with high-performance liquid chromatography. These active fractions were crystallized and identified to be the cyclic dipeptides cis-cyclo (L-Leu-L-Pro) and cis-cyclo(L-Phe-L-Pro) using gas chromatography-mass spectrometry; this identification was confirmed by X-ray crystallography. These cyclic dipeptides were identified in the culture filtrate of other lactic acid bacteria, including Lactobacillus spp., Leuconostoc spp., Weissella spp., and Lactococcus lactis.

Technological aptitude and applications of Leuconostoc mesenteroides bioactive strains isolated from Algerian raw camel milk

Two strains (B7 and Z8) of the Leuconostoc mesenteroides subspecies mesenteroides that were isolated from Algerian camel milk from an initial pool of 13 strains and demonstrated a high ability to inhibit the growth of Listeria spp. were selected and characterised at the phenotypic and genotypic levels. Probiotic profiling and inhibition spectra against food borne pathogens in mixed cultures were also investigated. The bacteriocin produced by L. mesenteroides strain B7 was identified as leucocin B by specific PCR. In vitro studies demonstrated that both Leuconostoc mesenteroides strains exhibited a marked probiotic profile, showing high survival at low pH (2-3 and 4) in the presence of 0.5%, 1%, and 2% of bile salts and at pH 3 in the presence of 3 mg/mL pepsin. Susceptibility testing against antimicrobial agents was also performed for both strains. When tested in a mixed culture with Listeria innocua, Listeria ivanovii, or Staphylococcus aureus, strain B7 reduced the numbers of these species by 1.87, 1.78, and 1.38 log units, respectively. Consequently, these two strains were found to possess good probiotic properties in vitro and a high capacity for Listeria spp. inhibition in mixed cultures. Therefore, these strains have a favourable technological aptitude and a potential application as novel probiotic starters.

Effect of acid lactic bacteria isolated from faeces of healthy dogs on growth parameters and aflatoxin B1 production by Aspergillus species in vitro

The aim of the present study was to evaluate the inhibitory effect of Enterococcus faecium and Lactococcus lactis subsp. lactis isolated from faeces of healthy dogs on (i) lag phase, (ii) growth rate, and (iii) aflatoxin B1 production by Aspergillus section Flavi on in vitro assays. Thirteen lactic acid bacteria (LAB) isolates were used as antagonist microorganisms. Antagonistic activity was assayed against four potentially aflatoxigenic Aspergillus section Flavi isolates: A. flavus (AF210 and AF281), A. parasiticus (AP245) and A. parasiticus (NRRL 2999). In general, the longest lag phases of Aspergillus isolates were obtained with E. faecium GJ40. Respecting the growth rate, no significant reduction was found in this parameter in the interaction assays with A. flavus and antagonist isolates respecting the control. While in A. parasiticus a significant reduction in growth rate was only observed in the interaction among reference strain and E. faecium MF5 isolate (p < 0.05). In general, AFB1 production was reduced by most of the LAB isolates assayed, except for E. faecium GJ18, GJ20, MF3 and MF4. This study provides the first data about the antiaflatoxigenic activity of autochthonous LAB isolated from dog faeces.

Antimicrobial activity of Bifidobacterium spp. isolated from healthy adult Koreans against cariogenic microflora

OBJECTIVE

Dental caries is the main common infectious disease in the human oral cavity. Streptococcus mutans and Streptococcus sobrinus were reported to be the most important etiological factors in human dental caries. Thus, we examined the inhibitory effects of Bifidobacterium spp. cells and culture supernatants against S. mutans and S. sobrinus, including Streptococcus gordonii, and Aggregatibacter actinomycetemcomitans, which is associated with periodontal disease.

METHODS

Mutans streptococci or A. actinomycetemcomitans and lactic acid bacteria (LAB) were mixed in 1:1 ratio and then incubated for 90 min at 37°C. After the incubation, the viability of mutans streptococci or A. actinomycetemcomitans was determined by plate count technique. We also investigated the morphological changes of S. mutans treated with LAB using scanning electron microscopy (SEM).

RESULTS

In vitro viability of S. mutans, S. sobrinus, S. gordonii, and A. actinomycetemcomitans was affected by human intestinal LAB identified as Bifidobacterium adolescentis SPM1005 and Bifidobacterium longum SPM1207. Especially, B. adolescentis SPM1005 cells at 1.0 × 10(8) CFU had a strong growth-inhibiting effect against S. mutans and induced a 64% loss of its viability (p<0.05). In addition, swollen and disrupted S. mutans were observed after incubation with B. adolescentis SPM1005. However, the culture supernatant of this strain did not show such inhibitory activity.

CONCLUSION

B. adolescentis SPM1005 cells decreased the growth of S. mutans, which is a risk factor for dental caries. Therefore, we suggest that this Bifidobacterium strain may be a useful probiotic microorganism for prevention of dental caries that does not have adverse effects.