Senior Scientist & Deputy Director
European Union Reference Laboratory (EU RL) for E. coli
Veterinary Public Health and Food Safety Department
Istituto Superiore di Sanità,
Viale Regina Elena 299 00161 Rome, Italy
Allelic profiling of the STEC accessory genome could provide a mean to investigate the evolution of the different groups of pathogenic E. coli.
Valeria Michelacci1, Massimiliano Orsini2, Arnold Knijn1, Sabine Delannoy3, Patrick Fach3, Alfredo Caprioli1, Stefano Morabito1
Shiga toxin-producing E. coli (STEC) cause a spectrum of diseases ranging from uncomplicated diarrhoea to haemorrhagic colitis (HC) and the life-threatening haemolytic uremic syndrome (HUS). STEC produce potent cytotoxins, Shiga-toxins (Stx), which block the protein synthesis eventually causing the death of the target cells. In spite of the striking biological effect exerted by Stx, their sole production seems to be not sufficient for the disease to occur, at least in its most severe forms. As a matter of fact, STEC associated with HC and HUS possess a large accessory genome made up of mobile genetic elements (MGEs) such as plasmids, phages and pathogenicity islands (PAIs). Amongst the many MGEs constituting the STEC virulome, three PAIs have been firmly associated with the STEC serogroups most frequently involved in severe disease: the locus for enterocyte effacement (LEE), the OI-122 and the OI-57.
Beside the presence of MGEs, a further source of variability is represented by the existence of multiple allelic variants of some of the virulence genes, which in some cases allowed for the identification of specific STEC subpopulations. This is the case of subtypes of stx2, the intimin-coding gene eae and the large gene toxB.
We used a high throughput qPCR methodology to identify all the different alleles of almost all the genes composing the LEE locus, the OI-122 and OI-57 PAIs. We also developed a bioinformatics pipeline to simultaneously compare the complete allelic profiles of the three PAIs and used it to study a large population of STEC. Our results show that this approach allows identifying different STEC subpopulations within single serogroups. Moreover, our findings provide additional evidence that two of the three PAIs co-evolved, reflecting the occurrence of their acquisition through a single event.
1European Reference Laboratory for E. coli, Department of veterinary public health and food safety, Istituto Superiore di sanità, 00161 Rome, Italy
2 Istituto Zooprofilattico Sperimentale dell’Abruzzo e Molise, Teramo, Italy
3 Anses (French Agency for Food, Environmental and Occupational Health and Safety), Food Safety Laboratory, IdentyPath platform, 14 rue Pierre et Marie Curie, Fr-94701 Maisons-Alfort, France.