Enterohemorrhagic Escherichia coli (EHEC) Findings from Humans in Finland

..............................................................................................................7 TIIVISTELMÄ..........................................................................................................9 LIST OF ORIGINAL PUBLICATIONS ..............................................................11 AUTHOR’S CONTRIBUTION .............................................................................12 ABBREVIATIONS .................................................................................................13 INTRODUCTION...................................................................................................15 REVIEW OF THE LITERATURE.......................................................................17 1. ESCHERICHIA COLI IN HEALTH AND DISEASE ..................................................17 1.2 Classification of diarrheagenic E. coli .................................................... 17 2. EHEC INFECTION IN HUMANS ........................................................................22 2.1 Occurrence of EHEC infections.............................................................. 22 2.2 Sources and vehicles of EHEC infections............................................... 24 3. EVOLUTION AND CLONALITY OF EHEC .........................................................24 4.VIRULENCE CHARACTERISTICS OF EHEC .......................................................28 4.1 Chromosomally located virulence characteristics ................................... 28 4.1.1 Shiga toxin (Stx) and stx variants......................................................... 28 4.1.2 Locus of Enterocyte Effacement (LEE) ............................................... 30 4.2 Plasmid mediated virulence characteristics............................................. 32 4.2.1 Enterohemolysin (Ehly) ....................................................................... 32 4.2.2 Putative type II secretion system (ETP) ............................................... 32 4.2.3 Katalase peroxidase (KatP) .................................................................. 33 4.2.4 Serine protease (EspP) ......................................................................... 33 4.2.6 Other chromosomal and plasmidal virulence factors ........................... 33 4.3. Transmission of virulence factors and bacterial species ....................... 34 5. SCREENING FOR EHEC...................................................................................34 6. SUBTYPING OF EHEC.....................................................................................37 6.1 Phenotypic methods ................................................................................ 37 6.2 Genotypic methods ................................................................................. 39 AIMS OF THE STUDY..........................................................................................42 MATERIALS AND METHODS............................................................................43 1. BACTERIAL STRAINS AND PATIENTS (I–V) .....................................................43 1.1 EHEC strains isolated from patients (I–V).............................................. 43 1.2 Reference strains (I–V) ........................................................................... 43 1.3 Data collection of the patients with EHEC infection (I–V)..................... 44 2. INVESTIGATION OF THE STOOLAND PURE E. COLI CULTURES (I–V) .............45 3. IDENTIFICATION OF THE EHEC ISOLATES (I–V) ............................................45 4. O:H SEROTYPING (I–V) ..................................................................................46 5. PHAGE TYPING OF O157 STRAINS (I, III–V) ...................................................46 6. DETECTION OF SHIGA TOXIN (STX) PRODUCTION (III, V) ..............................46 7. DETECTION OF ENTEROHEMOLYTIC (EHLY) ACTIVITY (II, III, V) ..................47 8. ANTIMICROBIAL SUSCEPTIBILITY TESTING (II)...............................................47 9. PULSED-FIELD GEL ELECTROPHORESIS (PFGE) (I, II, IV, V)..........................47 10. PCR-RESTRICTION FRAGMENT LENGTH POLYMORPHISM (RFLP) (I,III-V) ..48 11. INTIMIN TYPING (V) .....................................................................................48 12. ADDITIONAL METHODS (V) .........................................................................49 13. STATISTICAL METHODS (II, III, IV) ..............................................................49 RESULTS.................................................................................................................56 1. OCCURRENCE OF EHEC INFECTIONS (I–V)....................................................56 2. DEMOGRAPHIC DATA OF THE PATIENTS (I–V)................................................56 3. PHENOAND GENOTYPIC CHARACTERISTICS OF STRAINS (I–V) .....................57 3.1 O157 strains (I, III–V) ............................................................................ 57 3.2 Non-O157 strains (II, III, IV).................................................................. 59 4. VIRULENCE PROFILES OF EHEC STRAINS (III) ...............................................60 5. GEOGRAPHICAL DISTRIBUTION AND INCIDENCE OF DOMESTIC EHEC INFECTIONS (IV) .......................................................................................62 6. VEHICLES FOR AND TRANSMISSION OF EHEC INFECTION (IV) ......................62 DISCUSSION ..........................................................................................................65 1. EPIDEMIOLOGY OF EHEC INFECTIONS...........................................................65 2. MICROBIOLOGICAL PROPERTIES OF EHEC STRAINS ......................................67 3. TRANSMISSION AND VIRULENCE OF EHEC STRAINS......................................69 4. SOURCES OF EHEC INFECTIONS.....................................................................70 KEY FINDINGS AND CONCLUSIONS..............................................................72 ACKNOWLEDGEMENTS....................................................................................73 REFERENCES ..........................................................................................................75