Verotoxigenic Escherichia coli isolated from human samples in Slovenia

Abstract

BACKGROUND Shiga toxin-producing E. coli or Vero cytotoxin-producing E. coli (VTEC) are characterised by the ability to produce either one or both cytotoxins referred to as Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2). VTEC infection may result in life-threatening conditions such as haemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). Due to different methods of monitoring and identification of these bacteria in recent years, the existing data on reported cases of VTEC infections probably do not reflect reality. Our study of VTEC strains isolated in different regions of Slovenia, showed serogroups, major virulence factors and specific epidemiological data that can serve as a basis for further laboratory and epidemiological surveillance of VTEC infections. METHODS A total of 66 VTEC strains, isolated from stool samples of patients with diarrhoea from the year 1993 to 2009, were collected at NIPH (National Institute of Public Health). The data of patient’s age and gender, onset of illness and clinical manifestation of disease were gathered. The serogroups of isolated strains were determined with antisera following manufacturer’s instructions. The ability to produce verocytotoxins was tested using the reversed passive latex agglutination method. The presence of genes for intimin (eae), enterohaemolysin (ehxA) and verotoxins (vtx1 and vtx2) were determined by polymerase chain reaction (PCR). RESULTS Infection with VTEC was encountered throughout the year, but most people were ill in the summer and autumn months. More than half of patients (57.6 %) were younger than five years. Collected VTEC strains belonged to serogroups O17, O26, O91, O103, O111, O113, O126, O128, O145, O148 and O157 (the most frequent were O157 and O26). A high percentage of VTEC strains showed the presence of intimin (86.4 %) and enterohaemolysin (86.4 %) genes. The gene for vtx1 was found in 22.7 % of strains, the vtx2 in 57.6 % of strains, while the presence of both genes was determined in 19.7 % of strains. The presence of the vtx2 gene was determined in all strains associated with HUS and TTP, most of them possessed the eae and ehxA genes too. These patients were mostly older people and young children. CONCLUSIONS Most infections with VTEC occurred in the warmer months of the year, most patient were small children. The severity of VTEC infection is determined by several factors such as the E. coli serogroup, the type of Shiga toxin produced and presence of other virulence genes. The most common serogroups among the study strains were O157 and O26. VTEC O26 has been the most commonly isolated serogroup in recent years, nevertheless more and more different serological groups began to emerge. In all strains associated with HUS and TTP, the vtx2 gene was determined. Further typing of verocytotoxin encoding genes will contribute to assess the risk for complications with VTEC infection. The study provides insights about the age of the patients, seasonal distribution of disease, serogroups and genotypes of the agent.