Differences in virulence among Escherichia coli O157:H7 strains isolated from humans during disease outbreaks and from healthy cattle.
Escherichia coli O157:H7 causes life-threatening outbreaks of diarrhea, hemorrhagic colitis, and hemolytic-uremic syndrome in humans and significant economic loss in agriculture and could be a potential agent of bioterrorism. Although the prevalence of E. coli O157:H7 in cattle and other species with which humans have frequent contact is high, human infections are relatively uncommon, despite a low infectious dose. A plausible explanation for the low disease incidence is the possibility that not all strains are virulent in humans. If there are substantial differences in virulence among strains in nature, then human disease may select for high virulence. We used a gnotobiotic piglet model to investigate the virulence of isolates from healthy cattle and from humans in disease outbreaks and to determine the correlation between production of Shiga toxin 1 (Stx1) and Stx2 and virulence. Overall, E. coli O157:H7 strains isolated from healthy cattle were less virulent in gnotobiotic piglets than strains isolated from humans during disease outbreaks. The amount of Stx2 produced by E. coli O157:H7 strains correlated with strain virulence as measured by a reduction in piglet survival and signs of central nervous system disease due to brain infarction. The amount of Stx1 produced in culture was not correlated with the length of time of piglet survival or with signs of central nervous system disease. We suggest that disease outbreaks select for producers of high levels of Stx2 among E. coli O157:H7 strains shed by animals and further suggest that Stx1 expression is unlikely to be significant in human outbreaks.
Baker
Diane R
DR
Department of Veterinary Science, South Dakota State University, Brookings, SD 57007, USA.
Moxley
Rodney A
RA
Steele
Mike B
MB
Lejeune
Jeffrey T
JT
Christopher-Hennings
Jane
J
Chen
Ding-Geng
DG
Hardwidge
Philip R
PR
Francis
David H
DH
D000704:Analysis of Variance; D000818:Animals; D020520:Brain Infarction / Q000382:microbiology; D002417:Cattle; D002490:Central Nervous System / Q000382:microbiology; D002522:Chlorocebus aethiops; D004196:Disease Outbreaks; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology*; D019453:Escherichia coli O157 / Q000378:metabolism / Q000472:pathogenicity*; D005243:Feces / Q000382:microbiology; D005856:Germ-Free Life; D006463:Hemolytic-Uremic Syndrome / Q000382:microbiology; D006801:Humans; D007082:Ileum / Q000382:microbiology / Q000473:pathology; D007150:Immunohistochemistry; D007668:Kidney / Q000382:microbiology; D022622:Shiga Toxin 1 / Q000378:metabolism; D022641:Shiga Toxin 2 / Q000378:metabolism; D013552:Swine; D014709:Vero Cells; D014774:Virulence
D022622:Shiga Toxin 1; D022641:Shiga Toxin 2