1. GI Microbiology
Bloody Diarrhea
Infectious Agents
Typical GI Infection

2. Bloody Diarrhea
• There are more than 75 causesofbloody diarrhea.
• Can you name some of the common ones????
• Salmonella • Ulcerative Collitis
• E. Coli (EHEC & EIEC)
• Crohn’s Disease
• Entamoeba (protazoa)
• Campylobacter • Ischemia
• Shigella • Drug Induced
• YersiniaEnterocolitica • Chemo/Radiotherapy
• C. difficle
• CMV w/ HIV • Neoplasm
• Bloody Diarrhea is SEECSY (sexy)

3. Bloody Diarrhea
• What do all these have in common?
• They all attack the cells of the GI tract (mostly
large intestine) and cause them to slough off.
• What questions will you ask your patient to tell
them apart?
• Acute vs. Chronic • Family disease history (cancer, IBD, etc)
• Previous attacks • Abdominal Pain, Vomiting, Fever, Weight
• Appearance: mucus, pus, color Loss, Anal Itch
• Recent Food and drug intake • Painful joints, Back pain, Eye problems,
• Meal Sharing – are they sick too Skin lesions
• Recent Travel – overseas, underdeveloped• Symptoms of Iron Deficiency
• Patient History (cancer, chemo, surgery,
HIV, etc)

4. Bloody Diarrhea – Infectious Agents
• Salmonella spp. Cafeteria/restaurant outbreaks, family gatherings. contaminated food/water
(eggs/poultry). Summer months. Very young and very old. Prodrome of fever, headache, myalgia and
abdominal cramps. Fecal WBCs (and RBCs, but not so much).
• EHEC contaminated food/water, meat, outbreaks in institutions, day care. Fever, abdominal cramps, very
bloody stools. Can be complicated by HUS (hemolytic uremic syndrome) and TTP (Thrombotic
thrombocytopenic purpura. Produces Shiga-like toxin to cause systemic effects as well. Fecal WBCs and
RBCs.
• EIEC Shiga-like dysentery with blood and mucus, due to E. coli that invade epithelial cells of people of all
ages, also producing vomiting, fever and chills. A few children develop HUS
• E.histolytica contaminated food/water, travel in developing countries. Sudden onset fever, abdominal
cramps, bloody diarrhea (amoebic dysentery). Fecal WBCs and RBCs.
• Campylobacter spp. Most common diagnosed cause of bacterial diarrhea. Backpacker’s diarrhea;
contaminated food/water. Summer months. ~1wk duration. Very young children, and young adults.
Prodrome of fever, headache, myalgia and abdominal cramps. Fecal WBCs and RBCs.
• Shigellaspp. person to person spread; within families, day care. Sudden onset fever, headache, myalgia,
abdominal pain. Produces Shiga toxin. Fecal WBCs and RBCs
• Y. enterocoliticaperson to person and contaminated food/water, day care outbreaks. Fever, RLQ
abdominal pain. Mimics appendicitis. Fecal WBCs and RBCs.
• C. difficileafter treatment with Antibiotics (especially clindamycin) and antimotility agents, and especially
in hospital setting. Fever, abdominal pain, bloody stools with specific odor. Fecal WBCs and RBCs. Toxin
destroys colonic mucosa.

5. Watery Diarrhea – Infectious Agents
• ETEC: Traveler’s Diarrhea, produces ST (heat stable)
and LR (heat labile) toxins
• VibrioCholerae: “Cholera,” comma-shaped
organism, rice-water diarrhea
• C. perfringens: also causes gas gangrene
• Protozoa: Giardia and Cryptosporidium
• Viruses: Rotavirus, adenovirus, norwalk virus
(norovirus)
• Which of these is the leading cause of severe
infantile diarrhea?? Rotavirus!

6. Bloody Vs. Watery Diarrhea
Bloody Diarrhea
Invasive organisms: Salmonella, Shigella and EIEC enter enterocytes, multiply in
their cytoplasm, and then spread to the next enterocytes while the
previous die by necrosis (necrosis --- so bleeding --- and reactive secretion
of water and mucus)
Toxins which lead to necrosis: Shigelladysenteriae with shiga toxin which
inhibits protein synthesis thus leading to the cell death (necrosis), also
EHEC which has shiga-like toxin
Watery Diarrhea - without invasion and necrosis
Bacteria cover absorptive surfaceso less is absorbed from the intestines
Decreased number of intestinal villi
Increase water and electrolytes secretion(due to toxins)
-Vibriocholerae with cholera toxin,
-ETEC with LT-I toxin which is like cholerae-toxin and acts via cAMP,
-ETEC with St-a toxin which acts via cGMP

7. General Features of GI Bacteria
Bacteria Gram Stain Shape Extra
Salmonella Gram Negative Rod Lactose negative, flagellar
motility
E. Coli Gram Negative Rod EHEC: HUS,shiga like toxin
EIEC: Invades colon
ETEC: Traveler’s Diarrhea, LT and ST toxins
Campylobacter Gram Negative Comma OxidasePositive, growth at 42o C
(jejuni) or S
Shigella Gram Negative Rod Lactose Negative, low ID50, Shiga
toxin
YersiniaEnterocol Gram Negative Rod Pseudo-appendicitis
itica
VibrioCholerae Gram Negative Comma Rice-water diarrhea
Clostridium Gram POSITIVE Rod, Also causes Gas Gangrene
Perfringens Spore
Clostridium Gram POSITIVE Rod, Pseudomembranous Colitis,
Deficle Spore Antibiotic Associated Diarrhea

8. General Features ofOther Bugs
Virus Genome Envelope
Rotavirus ds-RNA No #1 cause of fatal diarrhea in children
Adenovirus ds-DNA No Mostly URT infections
Norovirus ss-RNA No Epidemic gastroenteritis
Treatment??? HYDRATION!!!! Usually self-limiting, only last a few days
Parasite Disease Transmission Treatment
EntamoebaHisto Amebiasis: dysentry, Cysts in water Metronidazole and
lytica RUQ pain, liver Iodoquinol
abscess
Cryptosporidium Severe Diarrhea in Cysts in water Prevention by filtering
immuno, mild city supplies
otherwise
Giardia Giardiasis: foul- Cysts in water Metronidazole
smelling fatty
diarrhea

9. Gastroenteritis
• WIKI: aka gastric flu or stomach flu, is the inflammation of
the gastrointestinal tract, involving both the stomach and
the small intestine and resulting in acute diarrhea, nausea,
vomiting, cramps, etc. It is typically self-limiting.
• Norovirus is the leading cause, Rotavirus is second but
causes more deaths (more severe)
Colitis
• WIKI: refers to an inflammation of the large intestine
• Can be caused by bacterial infections, ischemia, IBD.
• Abdominal pain, loss of appetite, fatigue, diarrhea (often
bloody), cramping, fever, distention

10. GI Host Defense
GI tract barriers include the acid pH of the stomach and
the antibacterial activity of pancreatic enzymes, bile,
and intestinal secretions.
Peristalsis and the normal loss of epithelial cells remove
microorganisms. If peristalsis is slowed (eg, because of
drugs such as belladonna or opium alkaloids), this
removal is delayed and prolongs some infections, such
as symptomatic shigellosis.
Normal bowel flora can inhibit pathogens; alteration of
this flora with antibiotics can allow overgrowth of
inherently pathogenic microorganisms (eg, Salmonella
typhimurium) or superinfection with ordinarily
commensal organisms (eg, Candida albicans).