Week2: Bacterial GI infections Flashcards
List the most common bacterial species that cause gastroenteritis.
Gram neg bacilli -E coli: commensal -Vibrio spp. -Salmonella spp. -Shigella spp. -Campylobacter jejuni -Yersinia enterocolitica Gram positive Cocci -Staphlococcus spp.: commensal Gram positive bacili -bacillus anthracis, B. cereus -Clotridium spp. : C. dificil is comensal
Non inflammatory vs. inflammatory diarrhea
Non inflammatory/secretory -no WBCs or RBCs -local inflammation may be present: Il-8 and PMNs Inflammatory diarrhea -presence of WBCs: pmns and lymphocytes -may or may not have RBCs
Bacterial virulence factors
- exotoxins
-enterotoxins: alter intestinal secretory mechanism
-cytotoxins: destroy intestinal mucosal cells - Invasion
-allows intracellular replication
can pass cells lining GI and spread systemically - Endotoxin
-gram neg bacteria. Induces Il1 Il6 and TNFa
Top 5 pathogens causing GI infections and hospitalizations
- Hospitalizations: Salmonella (nontyphoidal)> norovirus > Campylobacter spp.> toxoplasma gondii > E coli (STEC) O157
- food borne illness: Norovirus, salmonella, clostridium perfringens, campylobacter, staph. aureus
Describe 6 types of pathogenic E. coli and their virulence factors
INFLAMMTORY Diarrhea
1. EPEC: Enteropathogenic. adherence to epithelial cells lining small intestine. Prevents absorption.
2. EAEC: enteroaggregative -aggregative adherence to epithelial cells, prevents fluid absorption
3. EIEC: Enteroinvasive-invasion, replication, destruction of epithelial cells. inv genes. Large intestines.
4. EHEC: enterohemorrhagic-shiga like toxin, destroy epithelial cells. HUS. systemic absorption. large intestine.
SECRETORY Diarrhea
5. ETEC: Enterotoxigenic- heat stable and/or heat labile enterotoxins inhibit intestinal uptake and stimulate hyper secretion of fluids respectively. Most common cause of traveller’s diarrhea (O157:H7)
EMETIC disease
6. DAEC: Diffuse adherent
General E. coli features
- Gram neg bacilli, facultative anaerob, lactose positive
- classified based on O (cell wall polysaccharide), H (flagellar), and K (capsular) antigens
- 1/3 traveler’s diarrhea caused by ETEC
Vibrio cholerae
- gram neg baciili
- marine environments
- causes severe rice water diarrhea
- cholera toxin causes hyper secretion of water and electrolytes through accumulation of cAMP. Binary toxin: B for binding and A for active component
- pili is a virulence factor
- Rx supportive therapy Antibiotics can be used to reduce severity
Salmonella spp.
- gram neg bacilli
- s. typhi and paratyphoid are exclusively human pathogens. transmitted via food/water contamination
- animal reservoir for others
- causes inflammatory diarrhea, and enteric fever
- virulence: adherence factors and invasion factors, survives phagocytosis, acid tolerance response
- always require hospital treatment
Shigella spp.
- gram neg bacilli
- human reservoir. person to person fecal oral transmission
- don’t nee many organisms to establish infection
- disease: diarrhea with RBCs, WBCs, mucus
- virulence: adherence and invasion factors, survives phagocytosis, Shiga toxin interferes with mRNA translation
- Rx antibiotics
Campylobacter jejuni
- gram neg bacilli
- flagella
- animal reservoir
- found in 50% of retail poultry
- diarrhea with blood and leukocytes, nausea, vomiting ab pain
- virulence: adhesins, cytotoxic enzymes, enterotoxins
- complication: Guillan-Barre syndrome because of antibody cross reactivity between olisaccharides and glycospingolipids in neural tissue
yersinia enterocolitica
- gram neg bacilli
- water, raw milk, animal reservoir
- enterocolitis: inflammatory diarrhea
- virulence: invasion factors (chromosome), enterotoxin, heat-stable, resistance to complement mediated phagocytosis, resistance to antibody mediated complement (plasmid)
- rx supportive therapy
Which bacterial toxins cause food poisoning?
- Staph aureus: food contaminated by handler. boiling kills bacteria but doesn’t inactivate toxin. Egg products, institutionalized food
- b. cereus
- clostridium
B cereus: emetic vs. diarrhea illness
gram pos baccili. ubiquitous in environment.
- Emetic: from heat stable enterotoxin in reheated rice.short duration 9hr.
- Diarrheal form: undercooked food containing bacteria producing heat labile enterotoxin. 24 hr duration. Toxin affects adenyl cyclase. meat and veggies.
Clostridium difficile
- gram pos. bacilli. anaerobic
- spore former
- Antibiotic associated diarrhea: C. difficile is a commensal. In person with altered intestinal flora (antibiotics), C difficile can compete and establishes overgrowth.
- antibiotic associated colitis (pseudomembranous colitis)
- Toxin A=enterotoxin causes hyper secretion of fluid and chemotaxis of granulocytes
- Toxin B=cytotoxin, induces depolymerization of actin with resultant loss of cytoskeleton in leukocytes and epithelial cells. Increases inflammatory response.
- Rx with vancomycin or metronidazole.
Foodbourne vs. infant botulism
- caused by clostridium botulinum- gram pos bacilli, anaerobic. spore forming
- Foodborne botulism: inadequately preserved canned food. Toxin type A-flaccid paralysis. Blurred vision and speech are first symptoms.
- Infant botulism: contaminated honey. Ingested spores germinante in GI tract of baby, bacteria multiply, toxin produced in vivo. Constipation, difficulty swallowing, floppy baby.
- spores ingested by adults may germinate, but growth is suppressed by competing microflora.
