Micriobiology of the GIT

Question 1

Pathogens common to the small intestine.

Answer 1

• Cholera, ETEC/EPEC, Staph. aureus, Giardia

Question 2

Pathogens common to the large intestine.

Answer 2

• Salmonella, Campylobacter, C. dificile, EHEC/EIEC

Question 3

What are the 4 main pathogenic strains of E. coli in relation to the intestinal tract? How does each cause damage?

Answer 3

• entero-toxigenic (ETEC): enterotoxins (heat labile and heat stable types); small bowel; traveler’s diarrhea; non-inflammatory
• entero-pathogenic (EPEC): adherence (no toxins); small bowel; diarrhea in children
• entero-hemorrhagic (EHEC): O157:H7; shiga-like toxin (AKA STEC); hemolytic-uremic syndrome; large bowel; dysentery
• entero-invasive (EIEC): invasion; large bowel; dysentery

Question 4

Which pathogenic E. coli strains are most important in terms of the global incidence of diarrhea? What about of developed countries?

Answer 4

• global: ETEC (50% of traveler’s diarrhea) and EPEC

- developed countries: EHEC

Question 5

What is the most common cause of food-associated diarrhea in the 1st world?

Answer 5

• salmonella, EXCEPT for the U.S. and U.K. where it is campylobacter

Question 6

Most cases of Salmonella are self-limiting, but which two strains are often invasive and cause a much more severe illness?

Answer 6

• S. typhi and S. paratyphi

- they cause Typhoid Fever by invading the Peyer’s patches

Question 7

Which pathogen is most commonly associated with poultry?

Answer 7

• campylobacter! NOT salmonella

- (88% of birds are infected with some pathogen; 63% w/ campylobacter, 16% with salmonella, and 8% with both)

Question 8

Why are Campylobacter infections quite common?

Answer 8

• because their infective dose is very low

Question 9

About 1 in every 1000 patients infected with Campylobacter develop which syndrome?

Answer 9

• Guillain-Barre syndrome; inflammation of the peripheral nerves resulting in ascending paralysis

Question 10

Which organism causes Cholera? Where is it commonly found? What type of classic diarrhea results?

Answer 10

• Vibrio cholerae
• found in endemic S.E. Asia, parts of Africa, and S. America
• patients have massive amounts of rice water stool diarrhea

Question 11

Shigellosis is primarily a disease of what age group? Which animals are reservoirs of shigella?

Answer 11

• children

- the only reservoirs are humans and primates!

Question 12

What is the most common cause of diarrhea in infants? In children?

Answer 12

• infants: viral infection (norovirus and rotovirus)

- children: ETEC and EPEC

Question 13

Which organisms do we fight with antiobiotics?

Answer 13

• Campylobacter, Shigella, C. dificile, and Typhoid

Question 14

Food poisoning is NOT the same as food borne infection; which 3 traits make up food poisoning? Which 2 organisms are commonly involved?

Answer 14

• ingestion of preformed toxins, treated with antitoxin, and does NOT usually involve diarrhea
• S. aureus and C. botulinum

Question 15

The major organism involved in Esophagitis is __________. Two other main causes are _______ and _______.

Answer 15

• major organism: Candida albicans

- other causes: HSV-1 and CMV

Question 16

Pathogens involved in non-inflammatory gastroenteritis.

Answer 16

• Staph aureus, Bacillus cereus, ETEC, Vibrio cholerae, Clostridium botulinum, Clostridium perfringens, rotavirus, norovirus, Giardia lamblia
• (large overlap with pathogens affecting the small intestine)

Question 17

Pathogens involved in inflammatory gastroenteritis.

Answer 17

• Campylobacter jejuni, Salmonella, Shigella, EPEC, EHEC, EIEC, Clostridium difficile

Question 18

Pathogens involved in penetrating enteric infection (which is similar to inflammatory enteritis, but worse).

Answer 18

• Typhoid/enteric fever via Salmonella typhi and Salmonella paratyphi
• Yersinia enterocolitica

Question 19

Staphylococcus aureus

Answer 19

• Gram positive cocci; clusters
• due to human contamination of food
• usually infects small bowel; non-inflammatory
• the S. auerus toxin (TSST) is a super antigen that is heat, trypsin, and pepsin stable and can cause toxic shock syndrome
• food poisoning is due to ingestion of preformed toxin

Question 20

Bacillus cerreus

Answer 20

• Gram positive rod; aerobic organism; spores
• due to unrefrigerated “left out” food, reheated rice
• non-inflammatory
• 2 types of toxins; type I (rice): vomiting; type II (meat and cream): diarrhea and some vomiting

Question 21

Clostridium

Answer 21

• Gram positive rod; obligate ANaerobic organism; spores
• usually infect the large bowel
• due to reheated meat (C. perfringens) and improperly canned foods (C. botulinum); these are non-inflammatory
• due to antibiotics (C. dificile); inflammatory

Question 22

Vibrio cholerae

Answer 22

• Gram negative rod; comma shaped highly motile
• usually infects the small bowel; non-inflammatory
• due to human fecal-oral contact; contaminated water
• endemic to developing countries
• massive quantity of rice water stool

Question 23

Describe the enterotoxin involved in Cholera.

Answer 23

• it’s an A-B subunit structure
• A: involved in the permanent ADP-ribosylation (inactivation) of GTP-binding protein of Gs, resulting in a permanent increase in cAMP levels = excess secretion
• B: binding domain to the host cell

Question 24

Campylobacter jejuni

Answer 24

• Gram negative rod; curved (comma or S shaped)
• usually infects the large bowel; inflammatory
• due to contaminated milk, water, undercooked poultry
• common cause of Guillain-Barre syndrome

Question 25

Salmonella

Answer 25

• Gram negative rod; aerobic organism; flagella
• usually infects the large bowel; inflammatory
• due to contaminated food of animal origin (many animal reservoirs)

Question 26

What is Hemolytic-Uremic Syndrome? Which organism can cause it?

Answer 26

• a triad of anemia, thrombocytopenia, and acute renal failure
• associated with the shiga-like toxin produced by EHEC/STEC
• damaged areas from the toxin develop microthrombi, resulting in mechanical hemolysis (anemia) and decreased renal blood flow; the microthrombi consume platelets = thrombocytopenia

Question 27

Mumps Virus

Answer 27

• a paramyxovirus
• causes parotitis (parotids), orchitis (testes), and aseptic meningitis
• sterility is therefore a potential complication
• can also cause acute pancreatitis
• “mumps makes your parotids as big as POM-poms”

Question 28

What type of virus is each hepatitis virus?

Answer 28

• HAV: RNA picornavirus
• HBV: DNA hepadnavirus
• HCV: RNA flavivirus
• HDV: RNA delta virus
• HEV: RNA hepvirus

Question 29

aHAV (IgM), aHAV (IgG), HBsAg, aHBs, HBcAg, aHBc, HBeAg, aHBe

Answer 29

• aHAV (IgM): best test to detect active HAV virus
• aHAV (IgG): indicates prior HAV infection and/or prior vaccination; protects against reinfection
• HBsAg: indicates HBV infection
• aHBs: indicates immunity to HBV
• HBcAg: antigen of the core of HBV
• aHBc (IgM): acute/recent infection of HBV
• aHBc (IgG): prior exposure to or chronic infection of HBV
• HBeAg: indicates active viral replication and high transmissibility
• aHBe: indicates low transmissibility
• (aHBc and aHBe will be present during the window period)

Question 30

Helicobacter pylori

Answer 30

• Gram negative rod; curved
• catalse, oxidase, and urease positive
• diagnose with urea breath test (because H. pylori converts urea to ammonia and CO2; patient ingests radio-labelled urea –> if radio-labelled CO2 is exhaled, the test is positive)
• causes gastritis and PUD; creates an alkaline environment for survival
• it is strictly a human reservoir!

Question 31

Virulence Factors of H. pylori

Answer 31

• catalase, SOD, urease, mucinase, Vac-A (cytotoxin, responsible for ulceration), Cag-A (reprograms infected cells to create a nicer environment, associated with increased risk of gastric cancer)