Case Study
MICR 420 Emerging and Re-Emerging
Infectious Diseases
S2010
Case 63
Presented by: Isabel Mena
Rachelle Montero and Phil Soto
Case Summary
• 8 year old male
• Symptoms: 2 days of diarrhea (worsening, 14
movements that day, bloody), dehydration, pain
on defecation, vomited once
• History: 6 days before he attended a cookout
where he ate a burger that was pink inside
• Labs:
• significant white blood cell count
• polymorphonuclear cells in methylene blue stain of feces
• positive stool guaiac- a test for blood in feces
Key Information Pointing to
Diagnosis
Patient presents with:
• Bloody diarrhea
• History of ingesting uncooked meat 6 days
previous to hospital admittance
Laboratory Tests:
• MacConkey-Sorbitol stool culture
The Diagnosis for Case 63
Hemorrhagic Colitis
caused by E. coli O157:H7
Microbiology E. coli O157 H7
• E. coli is a gram negative bacillus of the enterobacteriaceae family:
– Motile
– Fermentor
– Facultative anaerobe
• E. coli are a part of the human normal microbiota and only a few
strains are pathogenic
• Pathogenic strains are identified through serotyping by the Flagellar
antigen (H-antigen) and the O-chain on LPS (O-antigen) as well as
the capsular antigen (K-antigen)
• Virulence Factors:
–
–
–
–
Pili: attachment
Capsules: prevent phagocytosis
Endotoxin (LPS): Overproduction of cytokines
Enterotoxins: various kinds diarrhea
• E. coli O157 H7 is classified as Enterohemorrhagic
– produces the Shiga-like toxin
– sorbitol negative
Pathogenesis of E. coli O157: H7
Image courtesy of Helmholtz
Association of German Research
Centres
Pathogenesis cont.
•
Image courtesy of nature.com
Mohawk K.L. et al. 2010. Microbial
Pathogenesis, vol 48:131-142
• The experiment used mice with intact normal
flora and infected them with E. coli O157:H7
either orally or by intragastric administration.
– Infection by E. coli first begins in the cecum where it
colonizes and then the toxin passes into the blood
stream
– Intimin is a major virulence factor involved in
attachment to epithelial cells and toxins are released
upon attachment
Representative Figure
Diagnostic Tests for E. coli O157:H7
• Stool cultures using Sorbitol MacConkey (SMAC) agar
• On SMAC agar O157 colonies appear clear due to their
inability to ferment sorbitol, whereby the common E. coli
is presented by a normal flora.
• Stool guaiac test
– Hydrogen peroxide (oxidizes the
guaiac)
– Positive indicated by
color change
• Cytotoxicity assay
• The newer method is
detecting the O group by PCR
Therapy and Prognosis for E. coli
O157:H7
• Supportive care
– Hydration
– electrolytes
• Monitor renal function, hemoglobin, and platelets
closely.
• Renal replacement therapy
– Dialysis or kidney transplantation
• According to CDC studies indicate that
antibiotics may promote the development of
HUS.
Prevention of E. coli O157:H7
• Tighter inspections
of the
manufactures.
• Stop, look and
think before you
eat your next meal.
Epidemiology
– Major sources are spinach and undercooked ground
beef.
– Easily spread from person to person
Threats
– Estimated 73,000 cases annually in US; 2,100
hospitalizations, 61 fatal cases
– Hemolytic Uremic Syndrome in children and elderly
– Nationally reportable
– Other strains of E.coli are producing Shiga-like Toxins
What do we tell the patient:
• We notify the parents that the test results for
their son indicate that he has hemmorhagic
colitis caused by E. coli O157:H7
• Most likely caused by the uncooked burger he
consumed 6 days ago
• We will keep him under observation for 24hr
and treat him with trimethoprimsulfamethoxazole and fluids for his dehydration
• If improvements are shown during that time you
will be able to take him home.
Take Home Message
• Hemmorhagic colitis involves infection by the
bacteria E.Coli. O157 H7
• Typical symptoms are diarrhea, blood in feces and
dehydration.
• Diagnostics include a culture of stool specimen on
MacConkey sorbitol agar and a stool guaiac test.
• Therapy is based on supportive therapy: fluids and
electrolytes
• Prognosis could be fatal if HUS develops
• Prevention is to be aware of food before ingesting
• Transmission is most commonly through food (ex.
spinach and undercooked meat)
References
• http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5304a1.htm
• http://www.fda.gov/food/foodsafety/foodborneillness/foodborneillnes
sfoodbornepathogensnaturaltoxins/badbugbook/ucm071284.htm
• http://www.sciencedaily.com/releases/2009/03/090319102311.htm
• http://www.nature.com/nrmicro/journal/v8/n1/fig_tab/nrmicro2265_F
2.html
• http://www.cdc.gov/ecoli/
• Micr 420 Lecture 6 Dr. Nancy McQueen and Dr. Edith Porter 2010