Abstract
In the study presented here, we tested, how large a fraction of lysogenic culture was undergoing filamentation, which could indicate triggering of the SOS response or SOS-independent prophage induction that is also known to cause cell filamentation. Here, antibiotic stress was triggered by adding mitomycin C and oxidative stress was induced by hydrogen peroxide. Observation of bacterial cells under an optical microscope revealed more filamenting cells for lysogenic Escherichia coli than for strains not carrying a prophage. Moreover, the amount of filamenting cells depended not only on the stress agents used and the type of the prophage, but also on the host. During induction of the 933W prophage, the resulting phage titer and the amount of elongating cells were different when using E. coli O157:H7 EDL933 clinical isolate and the E. coli MG1655 laboratory strain. The amount of filamenting cells correlates well with the observed phage titers.
Highlights
Enterohemorrhagic Escherichia coli (EHEC) is a highly pathogenic bacterial strain responsible for bloody diarrhea and hemorrhagic colitis
The culture was divided into three aliquots, where one was left as a control without any inducing agent, another one was supplemented with mitomycin C (Sigma-Aldrich) to the final concentration of 1 μg/ml, and the third one was supplemented with 3 mM H2O2
Cell filamentation occurs during the SOS response, but it can be a result of induction of prophage itself without triggering the SOS regulon
Summary
Enterohemorrhagic Escherichia coli (EHEC) is a highly pathogenic bacterial strain responsible for bloody diarrhea and hemorrhagic colitis. Since the stx genes are effectively expressed after prophage induction and during subsequent lytic development of the phage, studies on bacterial response to different stress conditions may help to understand the pathogenicity of EHEC. Conditions where the bacterial SOS response is activated lead to prophage induction in case of many phage groups, including lambdoid prophages. Shiga toxin production depends on an antibiotic used, and on a given strain (Grif et al 1998). Different classes of antibiotics have been tested for their influence on the Shiga toxin production by E. coli O157:H7 EDL933 strain. Streptomycin, sulfamethoxazole, and ciprofloxacin strongly increase the stx gene expression (McGannon et al 2010; Grif et al 1998)
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