P140: Probiotic Lactobacillus produces small-molecule inhibitors of Staphylococcus aureus quorum sensing and the staphylococcal superantigen toxic shock syndrome toxin-1

The production of the staphylococcal superantigen toxic shock syndrome toxin-1 (TSST-1) by Staphylococcus aureus has been associated with essentially all cases of menstruation-associated toxic shock syndrome (TSS). Here we show that Lactobacillus reuteri RC-14, a well-defined probiotic isolated from the human vagina, produces small signaling molecules that are able to interfere with the staphylococcal quorum-sensing system agr, a key regulator of virulence genes, and independently repress the expression of TSST-1 in S. aureus MN8, a prototype of menstrual TSS S. aureus strains. Quantitative real-time PCR data showed that transcription from the TSST-1 promoter (Ptst) in S. aureus MN8 was strongly inhibited in response to growth with L. reuteri RC-14 cultural supernatant as well as alterations in the transcriptional levels of the P2 and P3 promoters from all four agr S. aureus groups were also observed, indicating a potential influence of L. reuteri RC-14 signals on the production of secreted virulence factors in S. aureus. In addition, promoter-lux reporter plasmids were constructed, in which the expression of the luxABCDE operon was driven by different staphylococcal promoters including Ptst, P2, or P3. The effect of L. reuteri RC-14 on promoter activities was confirmed by the repression of luciferase activity upon the addition of L. reuteri RC-14 supernatant methanol extract, with no impact on the growth of S. aureus. The results from this work will contribute to a better understanding of interspecies cell-to-cell communication between Lactobacillus and Staphylococcus, and moreover, may lead to the development of novel anti-virulence strategies for S. aureus infection.