Enteric bacteria Flashcards
Actin polymerization organisms (2)
Shigella
Listeria (not in this unit)
Shigella bacteriology (gram, lactose, H2S, intra/extra cellular)
Gram (-) rod
Non-lactose fermenting
Non-H2S fermenting
Non-motile
Lactose fermenters (4)
CEEK
- Citrobacter
- Enterobacter
- Escherichia
- Klebsiella
Non-lactose fermenters (4)
ShYPS
Nonmotile, non-H2S producers
- Shigella
- Yersina
Motile, H2S producers
- Proteus
- Salmonella
Shiga toxin
Similar to EHEC shigella-like toxin
Produced by S. dysenteriae
3 activities: neurotoxic, cytotoxic, enterotoxic
- AB component toxin – inhibits protein synthesis by clipping 60S ribosomal subunit
Shiga toxin - complications
- HUS – occurs when the toxin starts to bind to kidneys
- Reactive arthritis (Reiter’s syndrome)
Shiga toxin - toxicities (3)
- Neurotoxic – to neurons
- Cytotoxic – to cells (in general)
- enterotoxic – to gut
Does this b/c it is an AB component toxin that inhibits protein synthesis at the 60S subunit
Is Shigella invasive?
Yes.
Invades the M cells (cells of Peyer’s patch) –> will cause bloody diarrhea once it begins invasion
Shigella - disease in humans
- extremely acid resistant (only need 1-10 organisms to start an infection)
- 1-4 day incubation
- Fever (generally > 101 F), first watery diarrhea followed by bloody diarrhea once the organism invades.
- invasion rarely causes septicemia, but it does cause shallow ulcers
Shigella - most severe strain
S. dysenteriae type 1 (has the Shiga toxin)
Non-infectious foodborne disease (3)
- S. aureus – toxin secreted into room temp food that patient later ingests
- B. cereus – rich/starches, also associated w/ foods left out too long
- C. botulinum – airtight-packed foods (flaccid paralysis)
Onset for all 3 are very fast (preformed toxin)
Salmonella - bacteriology
Gram (-) rod
motile, H2S (+)
oxidase (-), urease (-)
Seldom lactose fermenting
What predisposes you to Salmonella infections? (2)
- Impairment of mononuclear cells (ie Sickle cell)
- Decreased stomach acid
What species do you have to worry about in Salmonella?
S. typhi – typhoid fever
other subsets (many), but predominantly, S. enteritidis, and S. typhimurium
Is Salmonella sensitive to acid?
Yes. Need huge dose to catch it. (also why you are more susceptible to it if you have decreased stomach acid)
Fecal-oral transmission (from human carriers – gallbladder)
Salmonella typhi - pathogenesis
- Reaches M cells then travels around using macrophages
- Survives intracellularly and replicates in macrophages
- decreased fusion of lysosomes with phagosomes
- defensins (proteins) allow it to withstand O2-dependent and O2-independent killing
- Released from macrophages, the Vi capsular antigen (S. typhi only) withstands complement-mediated killing
- Tends to infect the biliary system and stay in the gallbladder (organisms enter the intestinal tract in bile)
Salmonella typhi - overall prognosis and treatment?
Causes typhoid fever, which isn’t that lethal, however the morbidity is very high (with a lot of fever, headache, abdominal pain
- Constipation is more common than diarrhea
Treat with: fluoroquinolones or 3rd gen cephalosporins
Salmonella typhi - what occurs more diarrhea or constipation?
Despite it being an enterobacteria, it commonly causes more constipation than diarrhea. Typically occurs first and then followed by diarrhea.
Salmonella typhi - complication(s)
- Necrosis of Peyer patches with perforation (local endotoxin triggered damage)
- thrombophlebitis
- cholecystitis
- pneumonia
- abscess formation
etc…
Salmonella typhi - which organ does it like the most?
Gallbladder – organisms can enter intestinal tract via bile
Salmonella typhi - prevention
Sanitation
Three vaccines (either against the S. typhi or against the polysaccharide capsule)
Salmonella typhi - how does it travel throughout the body?
In macrophages
- decreased fusion of lysosomes with phagosomes
- defensins (proteins) allow it to withstand O2 dependent and independent killing
- Vi capsular antigen withstands complement mediated killing
Salmonella - laboratory detection test
Antibodies to O, Vi and H antigens in patient’s serum can be detected by agglutination (Widal test)
- Vi antigen ONLY for typhi
Patient with fever, abdominal pain
Travel to an endemic area
Gram (-), encapsulated, nonlactose fermenter, produces H2S gas
Widal test
Salmonella typhi
What agar can be used to culture H2S (+) organisms? What is their appearance?
Hektoen agar
If H2S (+) –> black colonies
Chronic carriers of Salmonella typhi carry the bug where?
In their gallbladder
Salmonella typhi - clinical presentation
Rose collared spots (trunk/abdomen)
Constipation more common than diarrhea
Complications
- necrosis of Peyer patches w/ perforation (local endotoxin mediated)
- thrombophletitis
- cholecystitis
- pneumonia
- pea-soup diarrhea
