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
2
Q
Microbial pathogenic determinants are ____, ____, and ____
A
Microbial pathogenic determinants are adhesins, toxins, and factors that allow microbial invasion
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
4
Q
____ is most frequent etiology of traveler’s diarrhea
A
ETEC is most frequent etiology of traveler’s diarrhea
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)
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)
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
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
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)
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
11
Q
A
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
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
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
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
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
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
18
Q
Enterotoxigenic E. coli is ____ and _____
A
Enterotoxigenic E. coli is Gram-negative bacilli and a member of the Enterobacteriaceae family
19
Q
ETEC commonly causes ____
A
ETEC commonly causes traveler’s diarrhea
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
21
Q
Clostridium perfringens is an ____ ____ ____
A
Clostridium perfringens is an anaerobic Gram-positive bacillus
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
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
24
Q
Bacillus cereus is a ____ ____ and ____
A
Bacillus cereus is a Gram-positive rod and facultative anaerobe
25
Describe toxins of Bacillus cereus
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
26
Bacillus cereus is associated with consumption of ____ and antibiotics \_\_\_\_
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
27
28
Staphylococcus aureus food poisoning involves \_\_\_\_
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
Staphylococcus aureus food poisoning presents with ____ and ____ that subside after \_\_\_\_
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
Rotavirus is a ____ that accounts for a large portion of diarrhea requiring hospitalization in \_\_\_\_
Rotavirus is a dsRNA (Reoviridae) that accounts for a large portion of diarrhea requiring hospitalization in children
31
Rotavirus presents with \_\_\_\_, \_\_\_\_, and \_\_\_\_
Rotavirus presents with vomiting followed by diarrhea, fever, and respiratory symptoms
32
Rotavirus is diagnosed with ___ or ___ and prevented with \_\_\_
Rotavirus is diagnosed with stool ELISA or latex agglutination tests and prevented with an oral attenuated vaccine (RotaTeq or Rotarix)
33
Norovirus is transmitted via the ____ route, results from \_\_\_\_, and has an incubation period of \_\_\_\_
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
Norovirus presents with ____ and \_\_\_\_
Norovirus presents with nausea / vomiting / diarrhea and low-grade fevers
35
Norovirus is diagnosed via ____ or ____ and treatment is \_\_\_\_
Norovirus is diagnosed via enzyme-linked immunosorbent assay or PCR-based assays and treatment is usually not necessary
36
Giardia lamblia is a ____ with ____ and ____ forms
Giardia lamblia is a unicellular parasite with trophozoite and cyst forms
* Cyst form can survive for prolonged periods in the environment
37
Giardia lamblia is transmitted through \_\_\_\_, \_\_\_\_, and \_\_\_\_, and the parasite \_\_\_\_
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
Giardia lamblia symptoms include \_\_\_\_, \_\_\_\_, and ____ and last \_\_\_\_
Giardia lamblia symptoms include diarrhea, flatulence, and abdominal bloating / cramping and last 1-4 weeks
39
Describe diagnosis and treatment of Giardia lamblia
Giardia lamblia diagnosis and treatment
* Diagnosis: microscopic examination of stool specimens, enzyme immunoassay, nucleic acid amplification tests
* Treatment: metronidazole, tinidazole, nitazoxanide
40
Cryptosporidium is a \_\_\_\_, transmitted by the ____ route, and has a reservoir of \_\_\_\_
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
Cryptosporidium presents as ____ or \_\_\_\_
Cryptosporidium presents as acute self-limited diarrhea or chronic diarrhea leading to malabsorption in immunocompromised individuals
42
Describe diagnosis and treatment of Cryptosporidium
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
The causative organism is \_\_\_\_
The causative organism is Vibrio cholerae
44
Describe causes of inflammatory diarrhea
Inflammatory diarrhea causes
* Shigella spp.
* Salmonella enterica
* Campylobacter jejuni
* Enterohemorrhagic E. coli
* Yersinia enterocolitica
* Clostridium difficile
* Entamoeba histolytica
45
Shigella spp. are ____ and \_\_\_\_
Shigella spp. are Gram-negative rods and members of the family Enterobacteriaceae
46
Shigella spp. is transmitted by \_\_\_\_
Shigella spp. is transmitted by 5 F's: fingers, food, flies, feces, fomites
47
Describe determinants of pathogenicity of Shigella spp.
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
Some strains of Shigella spp. secrete ____ which is associated with hemolytic-uremic syndrome
Some strains of Shigella spp. secrete Shiga toxin which is associated with hemolytic-uremic syndrome
49
Shigella spp. presents as \_\_\_\_, \_\_\_\_, and \_\_\_\_
Shigella spp. presents as mild water diarrhea, bacillary dysentery (frequent painful defecation, blood and pus in feces), fever often present
50
Describe diagnosis, treatment, and prevention of Shigella spp.
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
Salmonella enterica is a ____ and \_\_\_\_
Salmonella enterica is a Gram-negative bacilli and member of the Enterobacteriaceae family
52
\_\_\_ causes food-poisoning epidemics and is associated with animal products such as chicken and eggs
Salmonella enterica causes food-poisoning epidemics and is associated with animal products such as chicken and eggs
53
Campylobacter jejuni is a ____ that causes \_\_\_\_, colonizes \_\_\_\_, and is acquired through \_\_\_\_
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
Describe diagnosis and treatment of Campylobacter jejuni
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
EHEC presents as \_\_\_\_, \_\_\_\_, and \_\_\_\_, and is associated with \_\_\_\_
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
Yersinia enterocolitica is a ____ and member of the \_\_\_\_
Yersinia enterocolitica is a Gram-negative rod and member of the Enterobacteriaceae family
57
Yersinia enteroclitica causes \_\_\_\_, is capable of \_\_\_\_, often leads to \_\_\_\_, and may lead to \_\_\_\_
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
Clostridium (Clostridioides) difficile is \_\_\_\_, \_\_\_\_, \_\_\_\_, and a major cause of \_\_\_\_
Clostridium (Clostridioides) difficile is a Gram-positive rod, anaerobic, spore-forming organism, and a major cause of antibiotic-associated diarrhea
59
Describe determinants of pathogenecity of Clostridium (Clostridioides) difficile
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
Describe clinical disease of Clostridium (Clostridioides) difficile
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
Abdominal cramping, tenderness, fever, leukocytosis, and diarrhea without gross blood is ____ infection
Abdominal cramping, tenderness, fever, leukocytosis, and diarrhea without gross blood is Clostridium (Clostridioides) difficile infection
* Leukocytosis is unique
62
Describe diagnosis, treatment, and prevention for Clostridium (Clostridioides) difficile
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
Entamoeba histolytica is an ____ that adheres ____ and has 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
\_\_\_\_ causes a flask-shaped ulcer
Entamoeba histolytica causes a flask-shaped ulcer
* Pore-forming toxin -\> lyses epithelial cells -\> flask-shaped ulcers
65
Describe results of ingestion of Entamoeba histolytica
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
The causative organism is \_\_\_\_
The causative organism is Campylobacter jejuni
67
\_\_\_\_ is the most likely cause of her fever
Clostridioides difficile is the most likely cause of her fever
68
Clostridium perfringens does NOT
