Sulfamethoxazole – Trimethoprim represses csgD but maintains virulence genes at 30°C in a clinical Escherichia coli O157:H7 isolate

Abstract

The high frequency of prophage insertions in the mlrA gene of clinical serotype O157:H7 isolates renders such strains deficient in csgD-dependent biofilm formation but prophage induction may restore certain mlrA properties. In this study we used transcriptomics to study the effect of high and low sulfamethoxazole–trimethoprim (SMX-TM) concentrations on prophage induction, biofilm regulation, and virulence gene expression in strain PA20 under environmental conditions following 5-hour and 12-hour exposures in broth or on agar. SMX-TM at a sub-lethal concentration induced strong RecA expression resulting in concentration- and time-dependent major transcriptional shifts with emphasis on up-regulation of genes within horizontally-transferred chromosomal regions (HTR). Neither high or low levels of SMX-TM stimulated csgD expression at either time point, but both levels resulted in slight repression. Full expression of Ler-dependent genes paralleled expression of group 1 pch homologues in the presence of high glrA. Finally, stx2 expression, which is strongly dependent on prophage induction, was enhanced at 12 hours but repressed at five hours, in spite of early SOS initiation by the high SMX-TM concentration. Our findings indicate that, similar to host conditions, exposure to environmental conditions increased the expression of virulence genes in a clinical isolate but genes involved in the protective biofilm response were repressed.

Pch Genes Control Biofilm and Cell Adhesion in a Clinical Serotype O157:H7 Isolate

“…In order to compare pchE expression in PA20 grown on agar surfaces at 30°C and 37°C, with and without exposure to 27× SMX-TM, total RNA was isolated and cDNA was made as previously reported ( Uhlich et al, 2018 ). Samples were tested in triplicate.…”

“…For biofilms, the mean optical density values of eluted CV at 590 nm (OD590) for each sample were analyzed as follows. For large screening assays testing the effects of multiple HTR regulators, samples were analyzed in R ( R Core Team, 2017 ) as previously described ( Uhlich et al, 2018 ). Strain variance was assessed with the Bartlett’s test and OD value differences were determined using the non-parametric Kruskal–Wallis test.…”

“…Exposure of clinical O157:H7 strains to DNA-damaging antibiotics, such as sulfamethoxazole-trimethoprim (SMX-TM), can potentiate HUS by increasing the expression of virulence genes encoded in prophage and prophage-like elements (e. g. stx 2 and LEE) ( Herold et al, 2005 ; Landstorfer et al, 2014 ; Uhlich et al, 2018 ). SMX-TM can also induce prophage excision from mlrA , making restoration of CsgD function a possible additional consequence of antibiotic treatment in the host ( Shaikh and Tarr, 2003 ; Uhlich et al, 2016 ).…”

“…SMX-TM can also induce prophage excision from mlrA , making restoration of CsgD function a possible additional consequence of antibiotic treatment in the host ( Shaikh and Tarr, 2003 ; Uhlich et al, 2016 ). However, in an RNA-seq study testing SMX-TM effects on a clinical O157:H7 transcriptome, SMX-TM had a slight repressive, rather than enhancing, effect on csgD functions in spite of strong induction of prophage and prophage-like genes ( Uhlich et al, 2018 ). The mechanism controlling the unexpected repressive csgD effects following SMX-TM exposure were not apparent but we reasoned that transcription factors differentially expressed during SMX-TM exposure might antagonize csgD .…”

“…In this study we tested several transcription factors encoded in HTR that were induced during SMX-TM treatment of O157:H7 clinical isolate PA20 ( Uhlich et al, 2018 ) for an effect on csgD , csgD -dependent cell adhesion, and biofilm properties.…”