Screening of lactic acid bacteria for bacteriocins by microbiological and PCR methods

Effectiveness of raw bacteriocin produced from lactic acid bacteria on biofilm of methicillin-resistant Staphylococcus aureus

Background and Aim

Probiotics are proven beneficial to health since they enhance immunity against dangerous pathogens and increase resistance to illness. Bacteriocin produced by lactic acid bacteria (LAB), demonstrates a broad inhibitory spectrum and therapeutic potential. This study aimed to isolate LAB-producing bacteriocin and investigate the effect of crude bacteriocin on biofilm from methicillin-resistant Staphylococcus aureus (MRSA).

Materials and Methods

This study used randomly collected 80 white soft local cheeses (40 each from cows and sheep) from different supermarkets in Basrah Province. The obtained samples were cultured and the bacterial suspension of S. aureus was prepared at 1.5 × 10⁸ cells/mL. The crude bacteriocin extracted from LAB was obtained, and the tube was dried and inverted to detect the biofilm loss at the bottom.

Results

There were 67 (83.75%) LAB isolates. Among 40 milk samples collected directly and indirectly, there were 36 (83.33%). Staphylococcus aureus isolates based on conventional bacteriological analysis and biochemical tests. Molecular testing was conducted to identify LAB and MRSA. Depending on genotypic results, the effect of white soft local cheese (cows and sheep) and the amplification results of the 16S rRNA gene were detected in 46 LAB isolates from white soft local cheese from cows and sheep. Based on the molecular identification of the mecA, results on Staphylococcus determined that only 2 of 36 isolates of S. aureus carried the mecA. Moreover, there were 26 (86.66%) isolates (MRSA) from samples of raw milk from local markets and subclinical mastitis in cows. The ability of LAB isolates was tested. The effects of bacteriocin production on preventing biofilm growth and formation were investigated. Results demonstrated that bacteriocin has high activity. Microtiter plates applied to investigate the ability of S. aureus to produce biofilms revealed that all isolates were either weak or moderate biofilm producers, with neither non-biofilm nor strong biofilm producers found among the tested isolates.

Conclusion

Lactic acid bacteria demonstrate a high ability to produce bacteriocin. Crude bacteriocin from LAB has a restrictive effect on biofilms produced by MRSA; thus, it can be used to reduce the pathogenicity of this bacterium.

Probiotic Activity of Enterococcus faecium and Lactococcus lactis Isolated from Thai Fermented Sausages and Their Protective Effect Against Clostridium difficile

Lactic acid bacteria, Enterococcus faecium and Lactococcus lactis, previously isolated from Thai fermented sausages were elucidated their probiotic properties especially in the control of Clostridium difficile 630. Both isolates survived in simulated gastric solution at pH 3 followed in simulated intestinal solution at pH 8. The presence of skimmed milk also helped the bacteria to survive through acidic and alkaline in gastrointestinal conditions. The adhesion properties of both isolates were tested using a human colon adenocarcinoma cell line. The result showed that both isolates exhibited desirable probiotic properties which adhered to Caco-2 cells. The neutralized cell-free supernatant of both isolates demonstrated that no cytotoxicity toward Caco-2 cells vice versa cell-free supernatant of C. difficile 630 toward Caco-2 cell demonstrated high toxicity. The immunomodulation effect in response to bacterial neutralized cell-free supernatant and cell-free supernatant was also studied. The expression level of pro-inflammatory cytokine of Caco-2 cell which are tumor necrosis factor-α and interleukin-8 was evaluated using quantitative reverse transcriptase PCR. Both isolates were able to diminish the expression level of TNF-α and IL-8 induced by the cell-free supernatant of C. difficile 630. Hence, these isolates would be able to improve the gut health through counteracting the C. difficile-associated intestinal inflammation in human cell lines. These results may contribute to the development of the isolates using as probiotics.

Partial Characterization of Bacteriocin Produced by Halotolerant Pediococcus acidilactici Strain QC38 Isolated from Traditional Cotija Cheese

During a screening of lactic acid bacteria producing bacteriocin from Cotija cheese, the strain QC38 was isolated. Based on the 16S rRNA gene nucleotide sequencing (516 pb accession no KJ210322) and phylogenetic analysis, the isolate was identified as Pediococcus acidilactici. Neutralized cell-free supernatant was tested for antimicrobial activity against 17 Gram-negative and Gram-positive pathogens. Growth inhibition was achieved against Listeria monocytogenes (supplier or indication or source), Staphylococcus aureus, Vibrio vulnificus, Vibrio cholerae O1 Ogawa, Vibrio cholerae NO 01 and Salmonella enterica subsp. Enterica serovar Typhimurium. Bacteriocin-like substance, after heating at 121°C for 15 min it remained stable and its antimicrobial activity was observed at pH ranging from 1.0 to 10.0 but inactivated by α-chymotrypsin and proteinase K. Strain QC38 was able to grow in 1-9% NaCl concentration. The plate overlay assay showed an approximate size of bacteriocin-like substance between 3.4 and 6.5 kDa. P. acidilactici QC38 harboured a plasmid that contains a gene for a pediocin (PA-1).

Bacteriocinogenic Bacteria Isolated from Raw Goat Milk and Goat Cheese Produced in the Center of México

Currently, there are few reports on the isolation of microorganisms from goat milk and goat cheese that have antibacterial activity. In particular, there are no reports on the isolation of microorganisms with antibacterial activity from these products in central Mexico. Our objective was to isolate bacteria, from goat products, that synthesized antimicrobial peptides with activity against a variety of clinically significant bacteria. We isolated and identified Lactobacillus rhamnosus, L. plantarum, L. pentosus, L. helveticus and Enterococcus faecium from goat cheese, and Aquabacterium fontiphilum, Methylibium petroleiphilum, Piscinobacter aquaticus and Staphylococcus xylosus from goat milk. These bacteria isolated from goat cheese were able to inhibit Staphylococcus aureus, Bacillus cereus, Escherichia coli, Listeria monocytogenes, L. inoccua, Pseudomona aeruginosa, Shigella flexneri, Serratia marcescens, Enterobacter cloacae and Klebsiella pneumoniae. In addition, bacteria from goat milk showed inhibitory activity against B. cereus, L. lactis, E. coli, S. flexneri, E. cloacae and K. pneumonia; S. aureus, L. innocua, S. agalactiae and S. marcescens. The bacteriocins produced by these isolates were shown to be acid stable (pH 2-6) and thermotolerant (up to 100 °C), but were susceptible to proteinases. When screened by PCR for the presence of nisin, pediocin and enterocin A genes, none was found in isolates recovered from goat milk, and only the enterocin A gene was found in isolates from goat cheese.

Isolation and characterization of bacteriocinogenic lactic bacteria from M-Tuba and Tepache, two traditional fermented beverages in México

Mexican Tuba (M-Tuba) and Tepache are Mexican fermented beverages prepared mainly with pineapple pulp and coconut palm, respectively. At present, reports on the microbiota and nutritional effects of both beverages are lacking. The purpose of this study was to determine whether M-Tuba and Tepache contain cultivable lactic acid bacteria (LAB) capable of producing bacteriocins. Tepache and M-Tuba contain mesophilic aerobic bacteria, LAB, and yeast. Bacillus subtilis, Listeria monocytogenes, Listeria innocua, Streptococcus agalactiae, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Salmonella typhimurium, and Salmonella spp, were the microorganisms most susceptible to metabolites produced by bacterial isolates. M-Tuba and Tepache contain bacteria that harbor genes coding for nisin and enterocin, but not pediocin. The presence of Lactococcus lactis and E. faecium in M-Tuba and Tepache, was identified by 16S rDNA. These bacteria produced bacteriocins of ∼3.5 kDa and 4.0–4.5 kDa, respectively. Partial purified bacteriocins showed inhibitory effect against Micrococcus luteus, L. monocytogenes, L. innocua, Str. agalactiae, S. aureus, Bacillus cereus, B. subtilis, E. faecalis, and K. pneumoniae. We characterized, for the first time, cultivable microbiota of M-Tuba and Tepache, and specifically, identified candidate lactic bacteria (LAB) present in these beverages that were capable of synthesizing antimicrobial peptides, which collectively could provide food preservative functions.

Qualitative detection of class IIa bacteriocinogenic lactic acid bacteria from traditional Chinese fermented food using a YGNGV-motif-based assay

In the present study, a YGNGV-motif-based assay was developed and applied. Given that there is an increasing demand for natural preservatives, we set out to obtain lactic acid bacteria (LAB) that produce bacteriocins against Gram-positive and Gram-negative bacteria. We here isolated 123 LAB strains from 5 types of traditional Chinese fermented food and screened them for the production of bacteriocins using the agar well diffusion assay (AWDA). Then, to acquire LAB producing class IIa bacteriocins, we used a YGNGV-motif-based assay that was based on 14 degenerate primers matching all class IIa bacteriocin-encoding genes currently deposited in NCBI. Eight of the LAB strains identified by AWDA could inhibit Gram-positive and Gram-negative bacteria; 5 of these were YGNGV-amplicon positive. Among these 5 isolates, amplicons from 2 strains (Y31 and Y33) matched class IIa bacteriocin genes. Strain Y31 demonstrated the highest inhibitory activity and the best match to a class IIa bacteriocin gene in NCBI, and was identified as Enterococcus faecium. The bacteriocin from Enterococcus avium Y33 was 100% identical to enterocin P. Both of these strains produced bacteriocins with strong antimicrobial activity against Listeria monocytogenes, Escherichia coli, and Bacillus subtilis, hence these bacteriocins hold promise as potential bio-preservatives in the food industry. These findings also indicated that the YGNGV-motif-based assay used in this study could identify novel class IIa bacteriocinogenic LAB, rapidly and specifically, saving time and labour by by-passing multiple separation and purification steps.

Curriculum and course materials for a forensic DNA biology course

The Forensic Science Education Programs Accreditation Commission (FEPAC) requires accredited programs offer a "coherent curriculum" to ensure each student gains a "thorough grounding of the natural…sciences." Part of this curriculum includes completion of a minimum of 15 semester-hours forensic science coursework, nine of which can involve a class in forensic DNA biology. Departments that have obtained or are pursuing FEPAC accreditation can meet this requirement by offering a stand-alone forensic DNA biology course; however, materials necessary to instruct students are often homegrown and not standardized; in addition, until recently, the community lacked commercially available books, lab manuals, and teaching materials, and many of the best pedagogical resources were scattered across various peer-reviewed journals. The curriculum discussed below is an attempt to synthesize this disparate information, and although certainly not the only acceptable methodology, the below discussion represents "a way" for synthesizing and aggregating this information into a cohesive, comprehensive whole.

The presence of sboA and spaS genes and antimicrobial peptides subtilosin A and subtilin among Bacillus strains of the Amazon basin

This report demonstrates the usefulness of PCR for the genes spaS and sboA as a means of identifying Bacillus strains with a potential to produce subtilin and subtilosin A. One collection strain and five Bacillus spp. isolated from aquatic environments in the Amazon basin were screened by PCR using primers for sboA and spaS designed specifically for this study. The sequences of the PCR products showed elevated homology with previously described spaS and sboA genes. Antimicrobial peptides were isolated from culture supernatants and analyzed by mass spectrometry. For all samples, the mass spectra revealed clusters with peaks at m/z 3300-3500 Da, corresponding to subtilosin A, subtilin and isoforms of these peptides. These results suggest that the antimicrobial activity of these strains may be associated with the production of subtilosin A and/or subtilin. The PCR used here was efficient in identifying novel Bacillus strains with the essential genes for producing subtilosin A and subtilin.