Enteric Bacterial Infections (Inflammatory): Cross, Ryan Flashcards
90% of infectious diarrheas are caused by bacteria, parasites, or viruses?
Viruses
Persistent diarrhea (>2 weeks) is likely caused by:
Parasite
When treating chronic diarrhea, start considering the possibility that the pt has:
HIV
or is infected with CMV, M. avium intracellulare
Bloody diarrhea =
You will see these cells in the stool:
Small or large volume?
Colon or SB affected, commonly?
inflammatory diarrhea aka dysentery
WBCs and RBCs
Small volume
Colon commonly affected
Watery diarrhea =
Colon or SB affected commonly?
Small or large volume
Colon or SB affected, commonly?
non-inflammatory diarrhea
No cells
Large volume
SB usually affected
7 pathogens causing inflammatory diarrhea:
Shigella EHEC EIEC Salmonella C. jejuni C. difficile Yersinia enterocolitica
List characteristics Salmonella, Shigella, and E. coli have in common.
Gram (-) facultative rods
- Ferment glucose–> acid
- oxidase neg.
- reduce nitrates to nitrite
- motile, except Shigella
Antigenic structures used in serotyping (eg. O157:H7):
H- flagellar antigens
O- side chain of LPS
3 species of Shigella. Which is most common in Central/South America?
How about the U.S.?
How is it transmitted? Low or high infectious dose?
C/S America- S. dysenteriae
U.S.- S. sonnei
Fecal oral route of infection or contaminated food/water
Low infectious dose
Discuss the pathogenesis of Shigella.
Resistant to acid of stomach.
Taken up by M cells, proliferate—> lyse cell and are taken up by macrophages—> induce apoptosis—> immune response that damages mucosa, allows for further invasion.
Moves from one cell to another by using F actin (formin) to rocket into adjacent cell.
Describe the clinical course of Shigella infection.
How do you treat it?
Self-limiting, lasts ~1 week.
50% become bloody diarrhea
Complications: reactive arthritis, urethritis, conjunctivitis (Reiter’s Syndrome)
Tx: Ceftriaxone, ciprofloxacin, azithromycin
List the 5 major strains of E. coli that cause diarrhea.
EHEC- enterohemorrhagic EAEC- enteroaggregative ETEC- enterotoxigenic EIEC- enteroinvasive EPEC- enteropathogenic
How do you get EHEC?
undercooked meat, contaminated veggies/milk. Human-human as well
Describe the pathogenesis of EHEC.
Has a pathogenicity associated island (PAI)
T3SS- injects PAI carrying receptor transcript into host cell
Pedestal forms and allows for bacterial attachment
—> Diarrhea
Describe the clinical course of EHEC.
Which strain is most likely to cause widespread outbreaks, HUS, and ischemic colitis?
Little fever, acute onset abd. cramps and watery diarrhea.
Watery diarrhea—> bloody diarrhea within 24 hrs and lasts 8 days.
O157:H7 MCC of E. coli assoc. outbreaks and HUS, ischemic colitis
EHEC produces this toxin:
What does this toxin do?
Shiga-like toxin
It is an AB toxin:
B subunit- binds toxin to receptor on cells
A subunit- enters cell and halts protein synthesis, causing cell death
Hemolytic Uremic Syndrome. What’s going on?
Feared complication of EHEC.
One of main causes of AKI in kids >3yo
Shiga-like toxin gets into blood stream where it alters endothelial cell function—> platelet aggregation
–> hemolytic anemia, thrombocytopenia
–> AKI w/ dialysis req’d in 1/2 pts (most regain KF)
–> seizures, somnolence in 25%
–> 5% die
Describe the Dx of EHEC and specifically, O157:H7 strains.
How do you ID presence of shiga-toxin?
Sorbitol-MacConkey agar
O157:H7 will be white colony
EHEC and other E. coli will grow pink
PCR for shiga-toxin
Tx for EHEC?
Supportive care w/ monitoring for complications
Avoid antidiarrheals
Abx not helpful and may induce more shiga-toxin release
Why is EIEC called enteroinvasive?
It enters intestinal cells and multiplies—> invades adjacent cells. Similarly to Shigella
This species of Salmonella causes typhoid fever:
Does it cause gastroenteritis?
S. enterica.
Does NOT cause gastroenteritis. Whereas non-typhoid Salmonella enteritidis does (food poisoning).
Describe vectors for Salmonellosis.
Main species to know?
S. enteritidis main species. Dairy Meat Poultry, eggs Pet reptiles Human-human
Describe the pathogenesis of Salmonellosis.
Attach to M cells and are endocytosed:
T3SS injects proteins that trigger endocytosis.
Leaves enterocyte and is phagocytosed by macrophages in LP–> apoptosis of MP triggers inflammatory response.
Describe the clinical presentation of Salmonellosis.
How do you Dx it?
Tx?
Incubation period 1-3 days
n/v/d, abdominal cramping, (may be bloody diarrhea. Gastroenteritis!
Fever in 50%
Illness lasts 3-4 days
5% will develop invasive dz that could lead to bacteremia, endovascular infxns, endocarditis, osteomyelitis, reactive arthritis. Predeliction for aortic plaques, bone prostheses.
Dx w/ stool culture.
Tx: age 2-50, supportive care
Fluoroquinolones for: HIV, immunocompromised, those at risk for disseminated, invasive dz, sickle cell dz, CVD, any prosthetic devices.
Causative agent of Typhoid (Enteric) Fever: Reservoir? Transmission? Young or old pts? Causes in the U.S.?
Salmonella enterica serotype typhi Humans only reservoir Transmitted human-human via fecal-oral, contaminated food/water Typically younger pts Foodborne in the U.S.
