Gram negative rods - Lactose non-fermenters Flashcards
What is the first step in differentiating gram negative rods that are not lactose fermenters?
Oxidase + = Pseudomonas
Where is psuedomonas found?
Nosocomial infections! Highly drug resistant.
Is pseudomonas aerobic?
Yes.
What is the name of the blue-green pigment pseudomonas produces?
Pyocyanin, pyoverdin.
What characteristic odor does Pseudomonas produce?
Sweet, grape-like odor.
What toxins does psuedomonas produce?
Endotoxin: fever/shock
Exotoxin A: inactivates EF-2 like diphtheria toxin
What clinical presentations are pseudomonas associated with?
BE PSEUDDO: Burns Endocarditis Pneumonia Sepsis Externa (otitis - swimmer's ear) UTIs Drug use Diabetes Osteomyelitis
In what scenarios does Pseudomonas cause folliculitis?
Hot tubs!
How can psuedomonas manifest in CF patients?
Pnuemonia - mucoid polysaccaride capsule may contribute due to biofilm formation.
Treatment?
Heavy duty abx. All the crazy ones.
Treatment for multi-drug resistant strains:
Colistin, polymyxin B.
What is ecthyma gangrenosum?
Rapidly progressive, necrotic cutaneous lesion caused by Pseudomonas – seen in immunocompromised pts.
If a gram + lactose non fermenter is also oxidase negative, what is the next step in differentiation?
TSI agar. If doesn’t produce H2S –> Shigella.
If does produce H2S–> Salmonella, Proteus, Yersinia
What is the reservoir of shigella?
Humans only.
How is shigella transmitted?
Fecal-oral transmission.
How does shigella spread in the body?
Cell to cell only, no hematogenous spread.
Is shigella motile?
No - no flagella, no H antigen.
What toxins does shigella produce?
- Shiga entertoxin : inactivates host 60S.
2. Endotoxin - fever, shock.
Does Shigella require a large or small infectious dose?
Low. Very small amount, resistant to gastric acid.
What is the presentation of Shigella?
Bloody diarrhea with mucus and pus.
What is the effect of abx on fecal excretion of shigella?
Shortens duration.
What immune response does shigella generate?
Primarily neutrophils.
Is there a vaccine for shigella?
No.
What are the four Fs of shigella?
Fingers, Flies, Food, Feces –> transmission routes.
What are the four subtypes of shigella, in order of decreasing severity?
Dystenteriae
Flexneri
Boydii
Somnei
How can shigella organisms cause severe disease without producing a lot of toxin?
Invasion.
What are the two types of Salmonella?
Typhi and Non-typhi
What is the difference in reservoirs between S. typhi and non-typhi?
S. typhi is in humans only, others can be found in animals as well.
What are common sources of non-typhi salmonella?
Poultry, eggs, pets, turtles.
How does salmonella spread?
Can disseminate hematogenously (unlike shigella).
Are salmonella motile?
Yes. (Salmon swim).
What are the virulence factors of Salmonella (non-typhi)?
Endotoxin
What additional virulence factor does Salmonella typhi have?
Vi capsule - protects from intracellular killing
Does salmonella require a low or high amount to cause disease?
High. Organism inactivated by gastric acid.
What is the effect of abx on fecal excretion of salmonella?
Prolongs duration, not recommended.
What is the immune response to salmonella typhi?
Primarily monocytes
What is the immune response to salmonella non-typhi?
PMNs in disseminated disease
Which salmonella type has a vaccine available?
Oral vaccine for S. typhi is live attenuated
IM for S. typhi contains Vi capsular polysacch
No vaccine for non-typhi salmonellas.
What is the presentation of typhoid fever?
Rose spots on abdomen, constipation, diarrhea, abdominal pain, fever.
How is typhoid fever treated?
Ceftriaxone or fluoroquinolone.
What does non-typhii Salmonella cause?
Bloody diarrhea.
Which salmonella is associated with a carrier state?
Typhi. Gallbladder colonization.
How is yersinia enterocolitica transmitted?
Zoonotic - from puppy feces, pigs, contaminated milk.
What is special about yersinia’s virulence factors?
Temperature sensitive - expressed at 37 degrees, can survive refrigeration.
What are the names of the yersinia’s antigens?
V and W antigens.
Is Yersinia motile?
Yes.
What kind of enterotoxin does yersinia have?
Enterotoxin similar to heat STABLE toxin on E. coli - increases cGMP levels, prevents resorption of NaCl.
What are the sx of yersinia?
Acute diarrhea, pseudoappendicitis –> this is due to mesenteric adenitis and/or terminal ileitis.
What is distinctive about proteus mirabilis’s metabolic properties?
Lactose neg, oxidase neg, indole neg.
Urease! Splits Urea into NH3 and CO2
What is the clinical manifestation of proteus?
UTI, urine has high pH due to urease.
Stones (ammonia magnesium phosphate).
What is the the Weil-felix test?
Uses Abs against strains of proteus to diagnose rickettsial disease – certain ricketsiae share similar antigens
