ppGpp and cytotoxicity diversity in Shiga toxin-producingEscherichia coli(STEC) isolates

Abstract

Shiga toxin-producing Escherichia coli (STEC) is a known food pathogen, which main reservoir is the intestine of ruminants. The abundance of different STEC lineages in nature reflect a heterogeneity that is characterised by the differential expression of certain genotypic characteristics, which in turn are influenced by the environmental conditions to which the microorganism is exposed. Bacterial homeostasis and stress response are under the control of the alarmone guanosine tetraphosphate (ppGpp), which intrinsic levels varies across the E. coli species. In the present study, 50 STEC isolates from healthy sheep were evaluated regarding their ppGpp content, cytotoxicity and other relevant genetic and phenotypic characteristics. We found that the level of ppGpp and cytotoxicity varied considerably among the examined strains. Isolates that harboured the stx2 gene were the least cytotoxic and presented the highest levels of ppGpp. All stx2 isolates belonged to phylogroup A, while strains that carried stx1 or both stx1 and stx2 genes pertained to phylogroup B1. All but two stx2 isolates belonged to the stx2b subtype. Strains that belonged to phylogroup B1 displayed on average low levels of ppGpp and high cytotoxicity. Overall, there was a negative correlation between cytotoxicity and ppGpp.

Diversity in E. coli (p)ppGpp Levels and Its Consequences

“…To date very few attempts have been made to analyze (p)ppGpp homeostasis in natural isolates of E. coli . In two of these studies, the basal level and starvation-induced levels of (p)ppGpp were assessed in a set of strains derived from the ECOR collection (Ferenci et al, 2011 ) and in a collection of Shiga toxin-producing E. coli (STEC) strains (Stella et al, 2017 ). The ECOR collection contains 72 strains from various locations and environments and from five phylogenetic groups (A, B1, B2, D, and E) that supposedly represents the variability in the E. coli species (Ochman and Selander, 1984 ).…”

“…x corresponds to the mean values, horizontal lines represent the median and the error bars correspond to 1 standard deviation; represent outliers. Data was extracted from Stella et al ( 2017 ).…”

“…In another analysis of (p)ppGpp fluctuation in natural isolates, ppGpp concentration was measured in 50 STEC strains growing under two different culture conditions—non-limited growth medium and phosphate starvation (Stella et al, 2017 ). A significant variability in ppGpp levels was observed among the STEC isolates ( Figure 2B ).…”

“…On the other hand, (p)ppGpp has been shown to inhibit stx phage replication, as the Δ relA Δ spoT double mutant displayed a higher degree of phage DNA replication and formed larger plaques on Δ relA Δ spoT lawns (Nowicki et al, 2013 ). A subsequent report has shown that intrinsic (p)ppGpp concentration is indeed inversely correlated with Stx toxin production, as STEC strains showing higher cytotoxicity toward Vero cells (the golden standard method for measuring toxin production and STEC virulence) usually contained lower levels of (p)ppGpp (Stella et al, 2017 ).…”

ppGpp and cytotoxicity diversity in Shiga toxin-producing Escherichia coli (STEC) isolates – CORRIGENDUM – ERRATUM

“…In the above-mentioned corrigendum [1], an incorrect DOI was given for the original article [2]. This has now been corrected.…”