Identification of the plasmid and the structural gene of colicin type 7 of Shigella sonnei

Colicin type 7 produced by majority of Shigella sonnei isolated from Thai patients with diarrhoea

Thirty one out of 153 strains of Shigella sonnei isolated from Thai patients with diarrhoea showed antibacterial activity against S. sonnei by agar well diffusion method. All of them harbor plasmids with the genetic determination of colicin type 7 (Js) gene but without colicin E and colicin U gene. The PCR product obtained from strain 35/44 was shown to be the gene for colicin type 7 lytic protein (cja). The partially purified bacteriocin (PPB) containing colicin type 7 of strain 35/44 was prepared and used for characterization. The antibacterial activity of PPB against a total of 17 selected Gram-positive and Gram-negative bacteria was tested. It was found that PPB of strain 35/44 was active against E. coli O157, S. sonnei and S. boydii. The sensitivity of PPB from this strain to proteinase K, trypsin and α-chymotrypsin suggests the proteinaceous nature of these antimicrobial substances. Therefore, this isolated bacterium can be regarded as bacteriocin producing bacteria. The bacteriocin produced by this isolated S. sonnei was heat stable as evidenced by its ability to maintain the activity at 80 °C for 60 min. In addition, it was stable within a wide range of pH (3–9). The molecular weight of colicin type 7 from isolated S. sonnei strain 35/44 analyzed by SDS-PAGE was 54.4 kDa composing of at least five subunits. It is to our knowledge; the first report of Thai patients with diarrhoea that S. sonnei isolated from them contained colicin type 7.

Isolation of bacteriocin-like substances producing bacteria from finished cattle-manure compost and activity evaluation against some food-borne pathogenic and spoilage bacteria

A finished compost sample was examined for bacteriocin-like substance production against five pathogenic bacteria: Salmonella typhimurium EF 85-9, Escherichia coli O157:H7 ATCC 43888, Enterococcus faecalis JCM 8726, Staphylococcus aureus JCM 2151, and Yersinia enterocolitica JCM 7577. At the preliminary detection of bacterial strains exhibiting antimicrobial activity from the compost sample, thirteen strains could be isolated. Screening of the inhibitory activity was done using agar-well diffusion assay and Microtiter plate growth assay. Six bacterial strains from the compost showed an antimicrobial activity against one or more of the tested indicator strains. Four strains (M1-M4) belonged to Shigella species and the other two strains (M5 and M6) belonged to Salmonella species. The antimicrobial activity was sensitive for alpha-chymotrypsin and papain. The antimicrobial substances from M3, M4 and M6 were heat stable when heated for 15 min at 121 degrees C with 100% relative activity. The bacteriocin-like substance produced by strain M2 was partially characterized. It exhibited an inhibitory activity against the tested food-borne pathogenic and spoilage bacteria, except Enterobacter aerogenes JCM 1235 and Lactobacillus plantarum subsp. plantarum JCM 1149. It was stable at a wide range of pH (3-11). There was no loss of activity for up to 3 weeks when stored at 4 and -20 degrees C or for up to 2 weeks when stored at 28 and -80 degrees C. This is the first report indicating the presence of bacteriocin-like activity in animal manure compost.