Abstract
Shiga toxins (Stx) induce the symptoms of the life-threatening hemolytic uremic syndrome (HUS) and are the main virulence factors of enterohemorrhagic Escherichia coli (EHEC). The bacterial SOS response is the essential signal for high level production and release of Stx1/2. To assess the potential effectiveness of different antibiotics in blocking SOS response and Stx1/2 production, we constructed a reporter gene based test system that allows for the time-resolved, simultaneous read-out of the SOS response (recAP-cfp) and Stx1 production (stx1::yfp) in EHEC O157:H7 EDL933. We find that cells exposed to inhibitory or subinhibitory concentrations of ciprofloxacin did induce the SOS response, but not when the cells were exposed to rifaximine, azithromycin, tetracycline, gentamicin or ampicillin. Cell lysis and the peak in Stx1 production were substantially delayed with respect to the peak of the SOS response. We used this feature to show that adding transcriptional or translational inhibitors can block Stx1 production even after the SOS response is fully induced. RT-qPCR based tests with other clinically relevant EHEC isolates showed similar results for both Stx1 and Stx2. These observations suggest that transcriptional and translational inhibitors may be of value in treating EHEC infections.
Highlights
Enterohemorrhagic Escherichia coli (EHEC) are foodborne pathogens
We found that ciprofloxacin addition to EHEC O157:H7 EDL933 increased the transcription of stx[1] by ~3-fold and stx[2] by ~7-fold (Fig. 4, Supplementary Fig. 8)
We examined the effect of antibiotic treatment on SOS and Shiga toxins (Stx)[2] production in two hemolytic uremic syndrome (HUS)-associated non-O157 EHEC strains, HUSEC-1, an O111:H10 strain and HUSEC-41, an O104:H4 strain that is very closely related to the strain that was responsible for a massive EHEC outbreak in Germany in 201115,16
Summary
Enterohemorrhagic Escherichia coli (EHEC) are foodborne pathogens. They are a significant cause of acute diarrheal illness with an estimated 2.8 million infections worldwide. While it is clear that transcriptional and translational inhibitors can be used to inhibit Stx production in vitro, several studies suggest that administration of any antibiotic increases the risk of severe EHEC-mediated disease[9,10] It is unknown whether Stx1/2 production (black dots) and SOS response (recAP-cfp, open diamonds) and Stx[1] expression (stx1::yfp, black diamonds) as increase of fluorescence over time (dF [A.U.]). We sought to determine if antibiotics that inhibit bacterial gene expression can be used to block Stx production either prior, or subsequent to activation of the host SOS system. To answer these questions, we used a reporter gene-based test system that allows for time-resolved, simultaneous monitoring of the SOS response (recAP-cfp) and Stx[1] production (stx1::yfp) in an EHEC O157:H7 EDL933 background. Our results suggest that antimicrobials that inhibit the bacterial gene expression apparatus could be the basis for a causative therapy for treating EHEC infections
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