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GI > SM_161b: Microbial Pathogens of the GI Tract > Flashcards

SM_161b: Microbial Pathogens of the GI Tract Flashcards

1
Q

Host defenses against GI pathogens are ____, ____, ____, and ____

A

Host defenses against GI pathogens are normal flora, gastric acid, intestinal motility, and cellular and humoral immune responses

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2
Q

Microbial pathogenic determinants are ____, ____, and ____

A

Microbial pathogenic determinants are adhesins, toxins, and factors that allow microbial invasion

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3
Q

Diarrhea is ____

A

Diarrhea is onset of ≥ 3 loose / liquid stools above baseline per 24 horu period

  • Infectious diarrhea acquired from: person-to-person, food, water
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4
Q

____ is most frequent etiology of traveler’s diarrhea

A

ETEC is most frequent etiology of traveler’s diarrhea

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5
Q

Describe inflammatory diarrhea

A

Inflammatory diarrhea

  • Mucus or blood in stool
  • Leukocytes and RBCs on microscopic examination
  • Results from local tissue destruction by a pathogen that invades the intestinal mucosa
  • Fever
  • Longer incubation period (2-4 days)
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6
Q

Describe noninflammatory diarrhea

A

Noninflammatory diarrhea

  • Watery / loose stools without mucus or blood
  • No leukocytes or RBCs on microscopic examination
  • Most often toxin-mediated or caused by viruses
  • No fever
  • Shorter incubation period (1-12 hours)
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7
Q

Describe causes of noninflammatory diarrhea

A

Noninflammatory diarrhea causes

  • Vibrio cholerae
  • ETEC
  • Clostridium perfringens
  • Bacillus cereus
  • Staphylococcus aureus
  • Rotavirus
  • Noroviruses
  • Giardia lamblia
  • Cryptosporidium
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8
Q

Vibrio cholerae is a ____ ____ that is spread via ____ and causes epidemics of ____

A

Vibrio cholerae is a curved Gram-negative rod (comma-shaped) that is spread via contaminated water and causes epidemics of cholera

  • Survives in marine crustaceans between epidemics
  • Most caused by serogroup O1 but most recent causes by O139 strain
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9
Q

____ is a cause of gastroenteritis following ingestion of uncooked seafood

A

Vibrio parahemolyticus is a cause of gastroenteritis following ingestion of uncooked seafood

(lives in salt water)

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10
Q

____ is a cause of gastroenteritis, wound infections, and bacteremia that lives in salt water

A

Vibrio vulnificus is a cause of gastroenteritis, wound infections, and bacteremia that lives in salt water

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11
Q
A
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12
Q

Describe determinants of pathogenecity of Vibrio cholerae

A

Vibrio cholerae determinants of pathogenecity

  • Ingestion (109-1010 bacteria required for infection)
  • Most are killed by acid in the stomach
  • Colonizes the small intestine: toxin co-regulated pili (TCP) - coregulated with cholera toxin, bacterial aggregation
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13
Q

Cholera toxin is an ____

A

Cholera toxin is an A-B toxin encoded by phage

  • TCP is phage receptor
  • 5 binding (B) subunits bind to cells -> endocytosis -> A1 released from A2 by reducrtion of disulfide bond -> A1 translocated into cell -> A1 ADP-ribosylates regulatory component of host adenylate cyclase -> upregulation -> increased cAMP in cells -> activates CFTR channel -> increased Cl secretion and decreased Na uptake -> secretory diarrhea
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14
Q

Describe Vibrio cholerae clinical disease

A

Vibrio cholerae clinical disease

  • Can result in severe dehydration and cause death in hours
  • Acquired by consumption of contaminated water or eating raw shellfish
  • Stool is water and contains mucus flecks (rice-water stools)
  • Fever is usually absent
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15
Q

Vibrio cholerae is diagnosed by ____

A

Vibrio cholerae is diagnosed by culturing on TCBS selective agar

  • TCBS: thiosulfate citrate-bile salts-sucrose selective agar
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16
Q

Vibrio cholerae is treated with ____ and ____

A

Vibrio cholerae is treated with rapid replacement of fluid / electrolytes and antibiotics

  • Antiobiotics shorten duration of symptoms: resistance now common to tetracycline/doxycycline, use macrolides (azithromycin) or ciprofloxacin
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17
Q

Vibrio cholerae prevention involves ____, ____, ____, and ____

A

Vibrio cholerae prevention involves treatment and disposal of human waste, purification of drinking water, cooking seafood, and oral live attenuated / killed vaccines

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18
Q

Enterotoxigenic E. coli is ____ and _____

A

Enterotoxigenic E. coli is Gram-negative bacilli and a member of the Enterobacteriaceae family

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19
Q

ETEC commonly causes ____

A

ETEC commonly causes traveler’s diarrhea

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20
Q

ETEC acts via ____ and ____

A

ETEC acts via heat labile toxin and heat stable toxin

  • Heat labile toxin: A-B toxin, similar to cholera toxin, stimulates adenylate cyclase in gut epithelial cells
  • Heat stable toxin: stimulates guanylate cyclase in gut epithelial cells
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21
Q

Clostridium perfringens is an ____ ____ ____

A

Clostridium perfringens is an anaerobic Gram-positive bacillus

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22
Q

Clostridium perfrigens results from ____ and has an incubation period of ____

A

Clostridium perfrigens results from ingestion of contaminated meat / poultry and has an incubation period of 6-12 hours

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23
Q

Clostridium perfringens diarrhea is associated with ____, is ____, and antibiotic therapy is ____

A

Clostridium perfringens diarrhea is associated with diarrhea and severe abdominal cramping, is self-limiting, and antibiotic therapy is NOT indicated

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24
Q

Bacillus cereus is a ____ ____ and ____

A

Bacillus cereus is a Gram-positive rod and facultative anaerobe

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25
Q

Describe toxins of Bacillus cereus

A

Bacillus cereus toxins

  • Toxins similar to LT toxin of E. coli: causes a similar diarrheal illness except with shorter incubation period (6-24 hours)
  • Toxin similar to staphylococcal enterotoxins: vomiting, short incubation period (1-5 hours)
  • Both result in water diarrhea
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26
Q

Bacillus cereus is associated with consumption of ____ and antibiotics ____

A

Bacillus cereus is associated with consumption of reheated rice and antibiotics are not indicated

  • Bacillus cereus spores in rice are resistant to boiling but germinate if rice is slowly cooled
  • Germinating organisms secrete the emesis-causing toxin that is resistant to reheating
  • Duration of symptoms < 24 hours
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27
Q
A
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28
Q

Staphylococcus aureus food poisoning involves ____

A

Staphylococcus aureus food poisoning involves ingestion of preformed heat-stable enterotoxin

  • Incubation period is short: 2-6 hours
  • Five enterotoxins: A, B, C, D, E
29
Q

Staphylococcus aureus food poisoning presents with ____ and ____ that subside after ____

A

Staphylococcus aureus food poisoning presents with vomiting and diarrhea that subside after 10-24 hours

  • Common source foods: ham, poultry, egg products, dairy products, bakery goods, casseroles
  • Antibiotics not useful b/c illness is caused by preformed toxin
30
Q

Rotavirus is a ____ that accounts for a large portion of diarrhea requiring hospitalization in ____

A

Rotavirus is a dsRNA (Reoviridae) that accounts for a large portion of diarrhea requiring hospitalization in children

31
Q

Rotavirus presents with ____, ____, and ____

A

Rotavirus presents with vomiting followed by diarrhea, fever, and respiratory symptoms

32
Q

Rotavirus is diagnosed with ___ or ___ and prevented with ___

A

Rotavirus is diagnosed with stool ELISA or latex agglutination tests and prevented with an oral attenuated vaccine (RotaTeq or Rotarix)

33
Q

Norovirus is transmitted via the ____ route, results from ____, and has an incubation period of ____

A

Norovirus is transmitted via the fecal-oral route, results from ingestion contaminated food or water, and has an incubation period of 12-48 hours

34
Q

Norovirus presents with ____ and ____

A

Norovirus presents with nausea / vomiting / diarrhea and low-grade fevers

35
Q

Norovirus is diagnosed via ____ or ____ and treatment is ____

A

Norovirus is diagnosed via enzyme-linked immunosorbent assay or PCR-based assays and treatment is usually not necessary

36
Q

Giardia lamblia is a ____ with ____ and ____ forms

A

Giardia lamblia is a unicellular parasite with trophozoite and cyst forms

  • Cyst form can survive for prolonged periods in the environment
37
Q

Giardia lamblia is transmitted through ____, ____, and ____, and the parasite ____

A

Giardia lamblia is transmitted through water (campers), food, or person-to-person (fecal-oral), and the parasite adheres to the epithelium of the small intestine to cause malabsorption

38
Q

Giardia lamblia symptoms include ____, ____, and ____ and last ____

A

Giardia lamblia symptoms include diarrhea, flatulence, and abdominal bloating / cramping and last 1-4 weeks

39
Q

Describe diagnosis and treatment of Giardia lamblia

A

Giardia lamblia diagnosis and treatment

  • Diagnosis: microscopic examination of stool specimens, enzyme immunoassay, nucleic acid amplification tests
  • Treatment: metronidazole, tinidazole, nitazoxanide
40
Q

Cryptosporidium is a ____, transmitted by the ____ route, and has a reservoir of ____

A

Cryptosporidium is a unicellular parasite, transmitted by the fecal-oral route, and has a reservoir of domestic animals

  • Causes limited bowel changes by microscopy
41
Q

Cryptosporidium presents as ____ or ____

A

Cryptosporidium presents as acute self-limited diarrhea or chronic diarrhea leading to malabsorption in immunocompromised individuals

42
Q

Describe diagnosis and treatment of Cryptosporidium

A

Cryptosporidium diagnosis and treatment

  • Diagnosis: acid-fast staining of stool, direct immunofluorescence antibody stains, enzyme immunoassays, PCR-based assays
  • Treatment: not necessary in the normal host, nitazoxanide has some activity in immunocompromised
43
Q

The causative organism is ____

A

The causative organism is Vibrio cholerae

44
Q

Describe causes of inflammatory diarrhea

A

Inflammatory diarrhea causes

  • Shigella spp.
  • Salmonella enterica
  • Campylobacter jejuni
  • Enterohemorrhagic E. coli
  • Yersinia enterocolitica
  • Clostridium difficile
  • Entamoeba histolytica
45
Q

Shigella spp. are ____ and ____

A

Shigella spp. are Gram-negative rods and members of the family Enterobacteriaceae

46
Q

Shigella spp. is transmitted by ____

A

Shigella spp. is transmitted by 5 F’s: fingers, food, flies, feces, fomites

47
Q

Describe determinants of pathogenicity of Shigella spp.

A

Shigella spp. determinants of pathogenicity

  • Tolerate stomach acid: ingestion of a few hundred bacteria sufficient to cause disease
  • Invade colon and cause an intense inflammatory response (diarrhea)
  • Bacteria invade host cells: transcytose through M cells, use type III secretion system to invade enterocytes from their basolateral surface
  • Intracellular bacteria escape vacuoles
  • Move through cytoplasm using host actin tails for propulsion - can also move into adjacent cells
  • Some strains secrete Shiga toxin associated with hemolytic uremic syndrome
48
Q

Some strains of Shigella spp. secrete ____ which is associated with hemolytic-uremic syndrome

A

Some strains of Shigella spp. secrete Shiga toxin which is associated with hemolytic-uremic syndrome

49
Q

Shigella spp. presents as ____, ____, and ____

A

Shigella spp. presents as mild water diarrhea, bacillary dysentery (frequent painful defecation, blood and pus in feces), fever often present

50
Q

Describe diagnosis, treatment, and prevention of Shigella spp.

A

Shigella spp. diagnosis, treatment, and prevention

  • Diagnosis: growth on routine stool culture
  • Treatment: fluoroquinolone, azithromycin
  • Prevention: sewage disposal, water chlorination, hand-washing, proper cooking of food
51
Q

Salmonella enterica is a ____ and ____

A

Salmonella enterica is a Gram-negative bacilli and member of the Enterobacteriaceae family

52
Q

___ causes food-poisoning epidemics and is associated with animal products such as chicken and eggs

A

Salmonella enterica causes food-poisoning epidemics and is associated with animal products such as chicken and eggs

53
Q

Campylobacter jejuni is a ____ that causes ____, colonizes ____, and is acquired through ____

A

Campylobacter jejuni is a Gram-negative rod (sea gull) that causes bloody diarrhea, colonizes animals, and is acquired through ingestion of contaminated food and poultry

54
Q

Describe diagnosis and treatment of Campylobacter jejuni

A

Campylobacter jejuni diagnosis and treatment

  • Diagnosis: suspected cases identified by presence of organism following Gram-staining of the stool, diagnosis is confirmed by stool culture using Campylobacter-selective media, NAATs
  • Treatment: only for severe infections, macrolides or fluoroquinolones
  • Rarely diarrhea may be followed by Guillain Barre syndrome
55
Q

EHEC presents as ____, ____, and ____, and is associated with ____

A

EHEC presents as bloody diarrhea, crampy abdominal pain, and no / low-grade fever and is associated with hemolytic-uremic syndrome

  • Hemolytic-uremic syndrome: hemolytic anemia, decreased number of platelets, renal failure, fever, and CNS dysfunction
56
Q

Yersinia enterocolitica is a ____ and member of the ____

A

Yersinia enterocolitica is a Gram-negative rod and member of the Enterobacteriaceae family

57
Q

Yersinia enteroclitica causes ____, is capable of ____, often leads to ____, and may lead to ____

A

Yersinia enteroclitica causes food poisoning, is capable of invading and disseminating, often leads to enlargement of the mesenteric lymph nodes, and may lead to bacteremia

  • Enlargement of the mesenteric lymph nodes may mimic appendicitis
58
Q

Clostridium (Clostridioides) difficile is ____, ____, ____, and a major cause of ____

A

Clostridium (Clostridioides) difficile is a Gram-positive rod, anaerobic, spore-forming organism, and a major cause of antibiotic-associated diarrhea

59
Q

Describe determinants of pathogenecity of Clostridium (Clostridioides) difficile

A

Clostridium (Clostridioides) difficile determinants of pathogenecity

  • Antibiotics suppress normal flora of colon
  • C. difficile overgrowth
  • Secretes 2 toxins (A and B): inactivate Rho GTPases -> lead to cell death and loss of barrier function
  • Antibiotics most commonly associated: clindamycin, ampicillin, cephalosporins, fluoroquinolones
60
Q

Describe clinical disease of Clostridium (Clostridioides) difficile

A

Clostridium (Clostridioides) difficile clinical disease

  • Diarrhea may occur while the individual is taking antibiotics or as late as 4 weeks after discontinuation
  • Severe infection associated with pseudomembrane formation (pseudomembranous colitis)
  • Patients quite ill
  • Often have abdominal cramping, tenderness, fever, leukocytosis, and diarrhea without gross blood
  • May progress to toxic megacolon and colonic perforation
61
Q

Abdominal cramping, tenderness, fever, leukocytosis, and diarrhea without gross blood is ____ infection

A

Abdominal cramping, tenderness, fever, leukocytosis, and diarrhea without gross blood is Clostridium (Clostridioides) difficile infection

  • Leukocytosis is unique
62
Q

Describe diagnosis, treatment, and prevention for Clostridium (Clostridioides) difficile

A

Clostridium (Clostridioides) difficile diagnosis, treatment, and prevention

  • Enzyme immunoassays (more convenient, detect toxin A only or both toxin A and B), PCR (detects gene encoding toxin B)
  • Oral vancomycin, relapse is common, bezlotoxumab (binds toxin B), fetal microbiota transplant
  • Avoid unncessary antibiotic use, contact precautions
63
Q

Entamoeba histolytica is an ____ that adheres ____ and has a ____

A

Entamoeba histolytica is an amoeba that adheres tightly to colonic epithelium and has a pore-forming toxin that lyses epithelial cells to cause flask-shaped ulcers

64
Q

____ causes a flask-shaped ulcer

A

Entamoeba histolytica causes a flask-shaped ulcer

  • Pore-forming toxin -> lyses epithelial cells -> flask-shaped ulcers
65
Q

Describe results of ingestion of Entamoeba histolytica

A

Entamoeba histolytica ingestion leads to

  • Aysmptomatic colonization
  • Infection localized to colon (amebiasis): chronic diarrhea, flatulence, and abdominal pain
  • Fulminant (immunocompromised): high fever, severe abdominal pain, and profuse diarrhea
  • Liver abscesses
66
Q

The causative organism is ____

A

The causative organism is Campylobacter jejuni

67
Q

____ is the most likely cause of her fever

A

Clostridioides difficile is the most likely cause of her fever

68
Q
A

Clostridium perfringens does NOT

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