SM_161b: Microbial Pathogens of the GI Tract Flashcards
Host defenses against GI pathogens are ____, ____, ____, and ____
Host defenses against GI pathogens are normal flora, gastric acid, intestinal motility, and cellular and humoral immune responses
Microbial pathogenic determinants are ____, ____, and ____
Microbial pathogenic determinants are adhesins, toxins, and factors that allow microbial invasion
Diarrhea is ____
Diarrhea is onset of ≥ 3 loose / liquid stools above baseline per 24 horu period
- Infectious diarrhea acquired from: person-to-person, food, water
____ is most frequent etiology of traveler’s diarrhea
ETEC is most frequent etiology of traveler’s diarrhea
Describe inflammatory diarrhea
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)
Describe noninflammatory diarrhea
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)
Describe causes of noninflammatory diarrhea
Noninflammatory diarrhea causes
- Vibrio cholerae
- ETEC
- Clostridium perfringens
- Bacillus cereus
- Staphylococcus aureus
- Rotavirus
- Noroviruses
- Giardia lamblia
- Cryptosporidium
Vibrio cholerae is a ____ ____ that is spread via ____ and causes epidemics of ____
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
____ is a cause of gastroenteritis following ingestion of uncooked seafood
Vibrio parahemolyticus is a cause of gastroenteritis following ingestion of uncooked seafood
(lives in salt water)
____ is a cause of gastroenteritis, wound infections, and bacteremia that lives in salt water
Vibrio vulnificus is a cause of gastroenteritis, wound infections, and bacteremia that lives in salt water
Describe determinants of pathogenecity of Vibrio cholerae
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
Cholera toxin is an ____
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
Describe Vibrio cholerae clinical disease
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
Vibrio cholerae is diagnosed by ____
Vibrio cholerae is diagnosed by culturing on TCBS selective agar
- TCBS: thiosulfate citrate-bile salts-sucrose selective agar
Vibrio cholerae is treated with ____ and ____
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
Vibrio cholerae prevention involves ____, ____, ____, and ____
Vibrio cholerae prevention involves treatment and disposal of human waste, purification of drinking water, cooking seafood, and oral live attenuated / killed vaccines
Enterotoxigenic E. coli is ____ and _____
Enterotoxigenic E. coli is Gram-negative bacilli and a member of the Enterobacteriaceae family
ETEC commonly causes ____
ETEC commonly causes traveler’s diarrhea
ETEC acts via ____ and ____
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
Clostridium perfringens is an ____ ____ ____
Clostridium perfringens is an anaerobic Gram-positive bacillus
Clostridium perfrigens results from ____ and has an incubation period of ____
Clostridium perfrigens results from ingestion of contaminated meat / poultry and has an incubation period of 6-12 hours
Clostridium perfringens diarrhea is associated with ____, is ____, and antibiotic therapy is ____
Clostridium perfringens diarrhea is associated with diarrhea and severe abdominal cramping, is self-limiting, and antibiotic therapy is NOT indicated
Bacillus cereus is a ____ ____ and ____
Bacillus cereus is a Gram-positive rod and facultative anaerobe
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
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
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
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
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
Rotavirus presents with ____, ____, and ____
Rotavirus presents with vomiting followed by diarrhea, fever, and respiratory symptoms
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)
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
Norovirus presents with ____ and ____
Norovirus presents with nausea / vomiting / diarrhea and low-grade fevers
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
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
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
Giardia lamblia symptoms include ____, ____, and ____ and last ____
Giardia lamblia symptoms include diarrhea, flatulence, and abdominal bloating / cramping and last 1-4 weeks
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
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
Cryptosporidium presents as ____ or ____
Cryptosporidium presents as acute self-limited diarrhea or chronic diarrhea leading to malabsorption in immunocompromised individuals
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
The causative organism is ____
The causative organism is Vibrio cholerae
Describe causes of inflammatory diarrhea
Inflammatory diarrhea causes
- Shigella spp.
- Salmonella enterica
- Campylobacter jejuni
- Enterohemorrhagic E. coli
- Yersinia enterocolitica
- Clostridium difficile
- Entamoeba histolytica
Shigella spp. are ____ and ____
Shigella spp. are Gram-negative rods and members of the family Enterobacteriaceae
Shigella spp. is transmitted by ____
Shigella spp. is transmitted by 5 F’s: fingers, food, flies, feces, fomites
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
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
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
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
Salmonella enterica is a ____ and ____
Salmonella enterica is a Gram-negative bacilli and member of the Enterobacteriaceae family
___ 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
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
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
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
Yersinia enterocolitica is a ____ and member of the ____
Yersinia enterocolitica is a Gram-negative rod and member of the Enterobacteriaceae family
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
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
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
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
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
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
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
____ causes a flask-shaped ulcer
Entamoeba histolytica causes a flask-shaped ulcer
- Pore-forming toxin -> lyses epithelial cells -> flask-shaped ulcers
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
The causative organism is ____
The causative organism is Campylobacter jejuni
____ is the most likely cause of her fever
Clostridioides difficile is the most likely cause of her fever
Clostridium perfringens does NOT
