Case StudyMICR 420 Emerging and Re-Emerging

Infectious DiseasesS2010

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 trimethoprim-sulfamethoxazole 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/

foodborneillnessfoodbornepathogensnaturaltoxins/badbugbook/ucm071284.htm

• http://www.sciencedaily.com/releases/2009/03/090319102311.htm• http://www.nature.com/nrmicro/journal/v8/n1/fig_tab/

nrmicro2265_F2.html• http://www.cdc.gov/ecoli/• Micr 420 Lecture 6 Dr. Nancy McQueen and Dr. Edith Porter 2010