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The aim of this research was to investigate the inhibitory effect of Bacillus subtilis P5-6 against Staphylococcus aureus on different states of standard medium with the presence of sodium chloride at high concentration, to develop an effective protective culture in food. Halophile Bacillus subtilis P5-6 isolated from Plara (Thai traditional salt fermented fish) contained both the genes encoding subtilin (spaS) and subtilosin (sboA). Only subtilosin gene expression was detected along with housekeeping gene BA-rpoB when co-cultured with Staphylococcus aureus. With the spot on lawn assay, cell suspension from the P5-6 culture showed inhibitory effect against Staphyloccus aureus, while no inhibition was observed when cell free supernatant was used. In liquid co-culture, the inhibitory effect of P5-6 on Staphylococcus aureus was observed when its inoculum size (population density of 8 log CFU/ mL ) was double that of S.aureus. In solid medium, Bacillus subtilis P5-6 could exert higher antagonistic action against this target pathogen. Bacillus subtilis P5-6 displayed an inhibitory effect even when its population was 2 log CFU/ mL lower than that of Staphylococcus aureus. Solid state cultivation with the presence of sodium chloride could enhance production and/or activity of bacteriocin of P5-6. The observation reflects an importance of the self-inhibitory effect as found in liquid and solid medium cultivation system. The data obtained could be fundamental importance in bacteriocin production development and application of protective culture from P5-6 to protect food against Staphyloccus aureus – one of the most common cause of foodborne disease.
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