Type III Secretion-Dependent Sensitivity of Escherichia coli O157 to Specific Ketolides.

Romina J Fernandez-Brando,Nao Yamaguchi,David L Gally,Sean P Mcateer,Dai Wang,Sally A Argyle,Trudi Gillespie,Marina S Palermo,Amin Tahoun

doi:10.1128/aac.02085-15

Abstract

A subset of Gram-negative bacterial pathogens uses a type III secretion system (T3SS) to open up a conduit into eukaryotic cells in order to inject effector proteins. These modulate pathways to enhance bacterial colonization. In this study, we screened established bioactive compounds for any that could repress T3SS expression in enterohemorrhagic Escherichia coli (EHEC) O157. The ketolides telithromycin and, subsequently, solithromycin both demonstrated repressive effects on expression of the bacterial T3SS at sub-MICs, leading to significant reductions in bacterial binding and actin-rich pedestal formation on epithelial cells. Preincubation of epithelial cells with solithromycin resulted in significantly less attachment of E. coli O157. Moreover, bacteria expressing the T3SS were more susceptible to solithromycin, and there was significant preferential killing of E. coli O157 bacteria when they were added to epithelial cells that had been preexposed to the ketolide. This killing was dependent on expression of the T3SS. Taken together, this research indicates that the ketolide that has accumulated in epithelial cells may traffic back into the bacteria via the T3SS. Considering that neither ketolide induces the SOS response, nontoxic members of this class of antibiotics, such as solithromycin, should be considered for future testing and trials evaluating their use for treatment of EHEC infections. These antibiotics may also have broader significance for treating infections caused by other pathogenic bacteria, including intracellular bacteria, that express a T3SS.

Highlights

A subset of Gram-negative bacterial pathogens uses a type III secretion system (T3SS) to open up a conduit into eukaryotic cells in order to inject effector proteins
The locus of enterocyte effacement (LEE) genes are encoded in 5 main operons (LEE1 to LEE5), and their induction is controlled by a complex network of regulators that includes the LEE-encoded regulator (Ler), which is encoded at the start of the LEE1 operon [4,5,6,7]
In order to assess the impact of solithromycin on the viability of bacteria expressing or not expressing a T3SS, ZAP193 and its ⌬LEE2 derivative (Table 1) were cultured overnight in LB and inoculated into MEM-HEPES to an optical density at 600 nm (OD600) of 0.5, at which point 3 ␮M solithromycin was added to the cultures and their optical densities were measured at 30-min intervals for 150 min

Summary

Introduction

A subset of Gram-negative bacterial pathogens uses a type III secretion system (T3SS) to open up a conduit into eukaryotic cells in order to inject effector proteins. These modulate pathways to enhance bacterial colonization. Considering that neither ketolide induces the SOS response, nontoxic members of this class of antibiotics, such as solithromycin, should be considered for future testing and trials evaluating their use for treatment of EHEC infections These antibiotics may have broader significance for treating infections caused by other pathogenic bacteria, including intracellular bacteria, that express a T3SS. Type III secretion systems (T3SSs) are expressed by a crosssection of Gram-negative bacterial pathogens to export effector proteins out of the bacterium and often directly into host eukaryotic cells. Certain classes of antibiotics are known to induce SOS responses, other antibiotics have successfully been used in outbreaks [28]

Methods

Results

Conclusion