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

SUMMARYShiga toxin-producingEscherichia 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 theE. colispecies. 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 thestx2 gene were the least cytotoxic and presented the highest levels of ppGpp. Allstx2 isolates belonged to phylogroup A, while strains that carriedstx1 or bothstx1 andstx2 genes pertained to phylogroup B1. All but twostx2 isolates belonged to thestx2b 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.