Development of Type III secretion system inhibitors

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As a part of screening by the assay utilizing TTSS-induced hemolysis in enteropathogenic Escherichia coli (EPEC), we have screened 20,250 microbial extracts and found that the extracts of the strain Streptomyces sp. K06-0806 and KK-88 showed potent TTSS inhibitory activity. After the fermentation and purification of the active compound, linear polyketides, aurodox and KK-88 compound, novel peptide, were isolated as TTSS inhibitors from the culture broths of K06-0806 and KK-88, respectively.The SDS-PAGE study showed that aurodox inhibited the expression of TTSS-related proteins, Tir, EspB, Map and EspF without the inhibition of EPEC viability and the expression of the house-keeping protein, GroEL The RT-PCR study of the genus of LEE (locus of enterocyte effacement) showed that aurodox reduced the transcription of many T3SS-related genes such as ler (LEE-encoded regulator), eae (LEE2: Type III apparatus), espA, espD, espB, espF (LEE4) and tir (LEE5) without reducing T3SS-nonrelated genes such as rrsB, one of 16S rRNA gene. Aurodox significantly reduced the transcription of ler, a gene of positive regulator of LEE, even at 0.5 μg/mL. This result suggests the specific inhibition of aurodox against the expression of T3SS-related proteins is caused by the inhibition of transcription of ler.In vivo study was carried out using C3H/HeJ mice infected by Citrobacter rodentium. Orally administrated aurodox caused murine survival with the repression of bacterial colonization in the intestinal mucosa. Therefore, aurodox is suggested to reduce the bacterial pathogenesis by the inhibition of T3SS.