Screening for Type III Secretion System Inhibitors

Commonly used antibiotics are becoming less effective since overuse creates a selective pressure for bacteria to become resistant, leading to the formation of “super bugs”. Some of these pathogenic bacteria include E. coli , Salmonella , Chlamydia and Yersinia species. These species utilize a type III secretion system (T3SS), which are needle-like structures on their surface used to inject host cells with toxins in order to evade our immune system and cause infection. Recently, a new method for testing compounds to determine if they inhibit the Y. pestis T3SS was developed by our lab. This method uses a special growth medium called Magnesium Oxalate (MOX) agar, which produces distinct growth characteristics based on the bacteria's ability, or inability, to secrete toxins. The goal of this research was to use this method to screen for antimicrobials produced by soil bacteria that may target T3SSs. Many species of bacteria found in soil produce antimicrobials in order to compete with each other for nutrients and space. Serial dilution plating was used to isolate soil bacteria and each isolate was patched onto MOX agar plates pre-inoculated with Y. pestis . After incubation, the areas around each soil isolate were analyzed for the Y. pestis growth characteristics associated with blocked T3S or growth inhibition. The soil bacteria that exhibited positive results were tested against ESKAPE pathogen alternatives and identified using 16S rDNA sequencing. Bacillus cereus strain JEM-2 and Bacillus amyloliquefaciens strain SSH100-3 were soil isolates identified to have antibacterial activity against Y. pestis .