E. coli bacteria belong to the family Enterobacteriaceae. They are gram-negative, facultative anaerobic, often peritrichous bacilli. They settle in the intestinal tract during the first hours after birth; in adults, however, they only represent 1 % of the intestinal flora. Due to their oxygen-using metabolism, they play an important role with regard to the symbiotic relationships between host organism and intestinal flora. In addition to the commensal intestinal microbes of the species E. coli, an increasing number of obligate pathogenic E. coli is described, some of which may cause fatal disease.
Shiga toxin producing E. coli (STEC, also designated as verotoxin-producing E. coli (VTEC)), including the enterohaemorrhagic E. coli (EHEC) associated with haemorrhagic colitis (HC) and haemolytic-uraemic syndrome (HUS), are able to produce cytotoxins (“cell poisons”), the so-called Shiga toxins. But also plasmid-encoded virulence factors and a pathogenicity island with a group of more than 40 chromosomal genes which is designated as „Locus of Enterocyte Effacement“ or LEE locus contribute significantly to the pathogenicity of EHEC. Particularly the eae gene (E. coli attaching and effacing) localized on the LEE which encodes an adherence factor called intimin is with some exceptions regularly found in highly pathogenic EHEC strains. Other non-LEE-encoded pathogenicity factors have been identified recently by extensive genomic analyses of EHEC bacteria. In Germany, an increasing spectrum of EHEC types has been registered over the past few years.
Cattle, other farm ruminants such as sheep and goats, and wildlife ruminants represent the main reservoir for STEC/EHEC. Undercooked beef, raw milk and raw milk products and non-pasteurized milk as well as other beef or dairy products are described as main sources of human infection. But also contaminations which are spread from chilled products (meat) to non-contaminated food products such as cooked sausages, as well as contaminated cold-pressed fruit juices and contaminated vegetables have been identified as sources of human infection. Furthermore, pastures contaminated with faeces of cattle harbouring the pathogen and cultivable land fertilized with cattle manure, where STEC/EHEC strains can survive for several months, must be considered as possible sources of infection. Bathing or drinking waters (wells) infiltrated with STEC/EHEC, e.g. from neighbouring pastures, can pose a significant risk of infection. Furthermore, the risk of infections by direct contact with animals (petting zoos, visits to agricultural enterprises, agrotourism) and faecal-oral transmission between humans, especially in shared accommodations must not be neglected.
In Germany, suspected human infection, human disease or death from enteropathic HUS are notifiable by name pursuant to Article 6 of the Infection Protection Act. Non-HUS EHEC diseases must be notified separately. In these cases, direct or indirect detection of EHEC strains is also notifiable by name, if the bacteria are considered to be responsible for acute disease.
STEC in animals must also be notified pursuant to the regulation on other reportable animal diseases.
The tasks of the national reference laboratory for verotoxin-producing E. coli include:
- Contact for federal and state authorities on questions relating to the epidemiology and control of verotoxin-producing E. coli
- Confirmatory testing
- Supply of reference material
- Evaluation, standardization and further development of diagnostic methods
- Participation in international proficiency ring trials
- Participation in EU proficiency ring trials
- Training of laboratory staff in STEC/EHEC diagnostics
- Cooperation in workgroups and research Projects
- Isolation of STEC/EHEC
- Characterization of STEC/EHEC strains by conventional and real-time PCRs
- Microarray-based characterization of STEC/EHEC strains
- Restriction fragment pattern analysis (RFLP) by pulsed field gel electrophoresis
- Multi-locus sequence typing (MLST)
- Genome sequencing of STEC/EHEC
- Shiga toxin detection by ELISA
- Shiga toxin detection by verocell test combined with verocell neutralization test
- Longitudinal studies on STEC/EHEC in cattle holdings
- Dynamics of STEC/EHEC in cattle holdings
- Genotypical characterization of long-term persistent STEC/EHEC strains
- Genome sequencing of long-term persistent STEC/EHEC strains
- Occurrence of STEC/EHEC in small ruminants
- Use of new methods for characterization (Microarray, MALDI-TOF)