Salmonella enterica is a pathogenic bacterium that causes disease in humans and animals, which is then treated with antibiotics. The inappropriate and excessive use of antibiotics has led to an increase in the number of bacterial strains with antibiotic resistance, which has led to the search for alternative antibacterial compounds. A possible solution would be probiotic bacteria such as B. subtilis, which are known to produce antimicrobial compounds, could be. In Master thesis, we have focused on the effect of S. enterica on the sporulation of
B. subtilis, as very little is known about their interaction. We investigated the interactions between the two bacteria, focusing on the survival rate and sporulation frequency of both bacteria when grown in cocultures. For this purpose, we used a method to determine the number of colony-forming units, while reporter fusions of the yellow fluorescent protein gene allowed us to monitor the expression of specific genes involved in sporulation. Gene expression dynamics were analysed by fluorescence spectrometry and flow cytometry. The results showed that the survival rate of B. subtilis in coculture with S. enterica was slightly lower compared to monoculture. After 24 hours, the frequency of sporulation was lower in the coculture. Late sporulation genes (e.g. spoIIQ) were less expressed in the coculture, while early sporulation genes (e.g. spo0A) showed similar activity in both conditions. The high expression level of Pspo0A-yfp in coculture suggested that sporulation may be delayed rather than inhibited in coculture. The repressor SinR was active all the time, while the promotor activities of PsinI and PspoIIAA where comparable to those of the control strains. This MSc thesis is one of the first studies on interactions between B. subtilis and S. enterica, showing that S. enterica delays sporulation of B. subtilis. Further studies are needed to confirm these findings and to understand the long-term effects.
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