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Abstract-Bacteriocins are antimicrobial peptides that help bacteria fight competing bacteria in microecological systems. Bacteriocins of lactic acid bacteria (LAB) have attracted much interest in recent years because of their properties that make them suitable as natural food preservatives against specific food pathogens, and as possible supplement to antibiotics against drug resistant bacterial strains. LAB bacteriocins are generally classified into the lantibiotics and non-lantibiotics, the latter divided into four subgroups. To date, only nisin and to a lesser extent, pediocin are the commercially applied bacteriocins for food use. Clinical applications are still limited to animal health. One of the more exciting prospects on the use of bacteriocins is the possibility of subjecting them to bioengineering to either increase antimicrobial activity or further specify their target microorganism. The latter would make it less damaging to the natural gut microflora, which is a common drawback of conventional antibiotic therapy. This paper focuses on the nature, biology, and applications of bacteriocins based on knowledge gained abroad and in the Philippines during the last two decades.

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Molecular tools were used to analyze the genetic diversity and population structure of Xanthomonas oryzae pv. oryzicola, the bacterial leaf streak pathogen of rice in the Philippines. Representative pathogen strains were selected and used to assess resistance in rice germplasm. A partial genomic library of X. oryzae pv. oryzicola was constructed, and a 459-bp clone containing the repetitive DNA element R41 was selected as a probe for restriction fragment length polymorphism (RFLP) analysis and sequenced. R41 shared 44% sequence homology with the putative transposase gene of IS1112, an insertion element cloned from X. oryzae pv. oryzae. Using R41 as a probe for RFLP analysis, 26 band profiles were discerned in a collection of 123 strains of X. oryzae pv. oryzicola. Analysis of PstI digestion patterns of DNA from the same collection resolved 36 haplotypes. Several clusters of strains were detected after grouping of data based on either pR41 as a probe or Pst1 digestion patterns. However, based on bootstrap analysis, the clusters were not robust. Genetic diversity was high for the entire collection as well as within spatially and temporally defined subsets of strains. Even a set of strains collected from a single site at a single time was highly diverse. Strains representing the different DNA types were inoculated to a set of diverserice cultivars. Consistent rice varietal groupings were obtained from disease reaction data, but there was no correlation between pathogen isolate cluster and host reaction across inoculation trials. Isozyme group I of rice, representing tropical japonica and javanica germplasm, is a promising source of resistance to bacterial leaf streak.

Probiotics research on lactic acid bacteria (LAB) continues to be paramount in the development of nutraceutical or functional foods. In this study, 47 selected Philippine plants having nutritional (edible such as vegetables) and/or medicinal values (therapeutic), were collected, from which selected fruit and leaves were subjected to LAB enumeration. Among these, 46.7% plant leaves reported to have strong antimicrobial property resulted in non-isolation of LAB while edible plant leaves with less or no antimicrobial properties generally gave numerous LAB isolates. Isolates coming from ripened guava (Psidium guajava L.), lobo-lobohan or cape gooseberry (Physalis peruviana L.) fruit, parsley (Petroselinum crispum), pandan (Pandanus amaryllifolius), spinach (Spinacea oleracea), leek (Allium ampeloprasum var. porrum) and niyog-niyogan (Quisqualis indica L.) leaves were identified through partial 16S rRNA analysis and tested for probiotic properties. Overall, Streptococcus luteciae Lb17 from ripe gooseberry fruit exhibited the highest antimicrobial activities against Staphylococcus aureus BIOTECH 1526, Escherichia coli O157: H7 BIOTECH 10311 and Bacillus cereus BIOTECH 1509. On the other hand, Enterococcus hirae (H and S63) from stevia were susceptible to streptomycin at minimum inhibitory concentration or MIC of 128 ug/mL). Lactobacillus plantarum F39 and all the other strains tested, meanwhile, was susceptible to ampicillin at MIC of 2 ug/mL and 0.125 ug/mL. Results were lower or equal to the established cut off value indicating the absence of antibiotic resistance genes among the identified strains, except for Pediococcus (Par5 and NN39) which showed resistance against streptomycin. Further investigation is needed to rule out the possibility of transfer of antibiotic resistance to pathogens present in the gut. All isolates tested were able to survive at artificial gastric juice (pH 2), revived at the simulated intestinal fluid (pH 8), and exhibited minimal titratable acidity and diacetyl production. For genetic screening of plantaricin genes, F39 possesses both plantaricin EF and plantaricin J, while Lactobacillus fermentum F36 has plantaricin EF. Both isolates were subjected to DNA fingerprinting. Such findings on the local isolates' probiotic properties suggest the possibility of incorporating them into different plant-based probiotic foods.

Bacteriocins are antimicrobial peptides produced by certain bacteria that can be alternatives to traditional antibiotics. This study aimed at evaluating large-scale bacteriocin production by the Pediococcus acidilactici strains in batch fermentation and to analyze the pediocin structural gene (papA) by bioinformatic methods. The fermentation using bacterial strains was carried out in Sartorius Biostat A-Plus Bioreactor, and the bacteriocin production was tested on Listeria innocua as a result of 24 h fermentation. The pediocin structural gene papA was amplified, and the amplicons of each strain were sequenced and analyzed to assess the secondary structure of pediocin and related metabolic pathways. It was shown that the papA structural gene sequence is a conserved region. All strains with a papA amplicon synthesis exhibited active bacteriocin synthesis Keywords: fermentation, Pediococcus acidilactici, purified bacteriocin, pediocin structural gene Funding - The authors acknowledge the grant support by the National Institutes of Molecular Biology and Biotechnology (BIOTECH), Laguna, Philippines.