SPECIFIC KETOLIDES DEMONSTRATE INCREASED CYTOTOXICITY FOR E. COLI O157 STRAINS EXPRESSING A TYPE 3 SECRETION SYSTEM AND INHIBIT EXPRESSION OF THE SYSTEM AT SUBMINIMUM INHIBITORY CONCENTRATIONS

MCATEER SP; FERNÁNDEZ BRANDO, ROMINA J; YAMAGUCHI, NAO; TAHOUN, AMIN; PALERMO, MARINA S; ARGYLE, SA; GALLY, DAVID

Boston

Congreso; 9th International Symposium On Shiga Toxin (Verocytotoxin) Producing Escherichia coli Infections.; 2015

VTEC

Introduction: Type 3 secretion systems (T3SS) areexpressed by a cross-section of Gram negative pathogens, such asenterohaemorrhagic Escherichia coli(EHEC) O157, to export effector proteins out of the bacterium often directlyinto host eukaryotic cells, thus modulating pathways to enhance bacterialcolonisation. In this study we screened established bioactive compounds for anythat could repress T3S expression by EHEC.Methods: The expression of T3S reporters(LEE1 to 5-GFP) and a growth status control (RpsM-GFP) were analysed in thepresence of established bio-active compounds. Initial screening of the NINDSlibrary was carried out with LEE1-GFP and RpsM-GFP reporters.  T3S was analysed by SDS-PAGE and Westernblotting.  Bacterial adherence, A/Elesion formation and viability were studied on Caco-2 and EBL cells.Results and Discussion: From the library screen, telithromycinshowed the greatest reduction in the LEE1 signal compared to the RpsM signal(LEE1, rpsM SD values): -5.0, -1.0. Subsequent research on a less toxicderivative, solithromycin, demonstrated that both ketolides inhibitedtranslation of T3S at sub-minimum inhibitory concentrations. We observedsignificant reductions (p<0.0001) in bacterial binding and A/E lesionformation on epithelial cells in the presence of telithromycin or solithromycinin a dose-dependent manner. Pre-incubation of epithelial cells with 5 µMsolithromycin resulted in significantly less attachment of EHEC (p<0.0001).  Moreover, bacteria expressing the T3SS weremore susceptible to solithromycin with preferential killing of EHEC expressingthe T3SS when added to epithelial cells pre-exposed to the ketolide. Takentogether, this research indicates that the ketolides may traffic back into thebacteria via the T3SS from a pool that accumulates in epithelial cells.  Implications: Considering that neither ketolide induces the SOS response, non-toxicvariants of this class of antibiotics, such as solithromycin, should beconsidered for the treatment of future EHEC outbreaks and more generally for otherbacteria that express these secretion systems.