credits bmbl December 7 '06.doc - Central Michigan University

Agent Summary Statements – Bacterial Agents
system has been developed for E. coli based the O (somatic) and H (flagellar) antigens
expressed by these organisms. Certain pathogenic clones of E. coli may cause urinary
tract infections, bacteremia, meningitis, and diarrheal disease in humans, and these clones
are associated with specific serotypes.
The diarrheagenic E. coli strains have been characterized into at least four basic
pathogenicity groups: Shiga toxin (Verocytotoxin)-producing E. coli (a subset of which
are referred to as enterohemorrhagic E. coli), enterotoxigenic E. coli, enteropathogenic E.
coli, and enteroinvasive E. coli. 123 In addition to clinical significance, E. coli strains are
commonly-used hosts for cloning experiments and other genetic manipulations in the
laboratory. This summary statement provides recommendations for safe manipulation of
Shiga toxin-producing E. coli strains. Procedures for safely handling laboratory
derivatives of E. coli or other pathotypes of E. coli should be based upon a thorough risk
assessment.
Occupational Infections
Shiga toxin-producing E. coli strains, including strains of serotype O157:H7, are a
demonstrated hazard to laboratory personnel. 133-138 The infectious dose is estimated to be
low—similar to that reported for Shigella spp., 10-100 organisms. 136 Domestic farm
animals (particularly bovines) are significant reservoirs of the organisms; however,
experimentally infected small animals are also sources of infection in the laboratory. 139
Verocytotoxin-producing Escherichia coli have also been in wild birds and rodents in
close proximity to farms. 140
Natural Modes of Infection
Cattle represent the most common natural reservoir of Shiga-toxin producing E.
coli. Transmission usually occurs by ingestion of contaminated food, including raw milk,
fruits, vegetables, and particularly ground beef. Human-to-human transmission has been
observed in families, day care centers, and custodial institutions. Water-borne
transmission has been reported from outbreaks associated with swimming in a crowded
lake and drinking unchlorinated municipal water. 139 In a small proportion of patients
(usually children) infected with these organisms, the disease progresses to hemolytic
uremic syndrome or death.
LABORATORY SAFETY
Shiga toxin-producing E. coli are usually isolated from feces. However, a variety
of food specimens contaminated with the organisms including uncooked ground beef,
unpasteurized dairy products and contaminated produce may present laboratory hazards.
This agent may be found in blood or urine specimens from infected humans or animals.
Accidental ingestion is the primary laboratory hazard. The importance of aerosol
exposure is not known.
Containment Recommendations
169