Case StudyMICR 420 Emerging and Re-Emerging

Infectious DiseasesS2010

Case 63Presented 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 admittanceLaboratory Tests:• MacConkey-Sorbitol stool culture

The Diagnosis for Case 63

Hemorrhagic Colitiscaused 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