Microbiology Flashcards
What are the two major classes of septic arthritis and which is more lethal; and why? Which microbes cause which types of infection?
Nongonococcal = high mortality rate.
Gonococcal = low mortality rate
*Less common lyme arthritis
Nongonococcal involves more inflammation (high number of PMNs) and pain. Usually monoarticular, most common in the knee.
Only Gonococcal we’ve learned is Neisseria gonorrhea the rest are non-gonococcal. (Usually G + Staph A, or G - Kingella kingae….)
Gonococcal-polyarticular, DGI, less joint damage, knee, wrist, ankle elbow.
What’s the most common way in which native joint infections (NJI) reach the joint? What’s more common NJI or a PJI?
hematogenous spread.
also- direct innoculation, bite or trauma
extension of ostemyelitis
PJI way more common
Describe the microbes that play a major role in prostetic infectious arthritis following PJI. Explain those common to early (1-3 months), delayed (3 months-2 yrs), and late (>2yrs) and why.
The most common two are Staph A, and Staph Epidermidis comprising 65% of PJI. Why? because they’re normal flora of the skin.
Early-more virulent- S. Aureus
Delayed- less virulent CoNS S.Epidermidis
Late-usually due to hematogenous seeding-(type?)
What are some features of S. Epidermidis that make it well adapted to PJI?
It has a loose slime layer that helps with attachment, as well as, adhesins (collagen, fibrinogen, elastin) and it forms biofilms that are difficult to destroy with antibiotics, decrease inflammatory response, and are harder to isolate a single microbe.
What’s unique about Neisseria Gonorrheas outer membrane?
It behaves more like a G+ due to the lipooligosaccaride layer and used to be susceptible to penicillins.
You have a 16 y/o patient who’s recently become sexually active, come into the clinic with a NJI of the hip. As part of the lab work up you draw blood samples for later culturing in the lab suspecting a gram neg, diplococcus bacteria. The lab tech should do which of the following?
A) plate on chocolate agar
B) plate on Thayer-Martin agar
C) Plate on Thayer-Martin agar with an antibiotic
D) Plate on blood agar
A) is correct. Neisseria gonorrhea is the most likely cause of this infection, but the Thayer-Martin agar (chocolate + antibiotic) is only needed if the sample was taken from a part of the body with multiple flora present (throat) not the blood which should be sterile.
B) not necissary in this case b/c blood sample
C) doesn’t make sense b/c thayer-martin already has antibiotic
D) left field.
What are the major virulence factors of N.gonorrhoeae?
IgA1 protease
facultative intracellular (pyogenic response) Inside PMNs!!
antigenic and phase variation Opa’s, pili, LOS
receptor binding at different points in infection
escape from immune surveillance
bind host sialic acid to their LOS. (sialic acid is connected to the surfaces of cells and soluble proteins)
outer-membrane blebbing
escape from immune surveillance, as blebbs look like outer membrane
What condition typically results in disseminated gonococcal infection (DGI)?
Pelvic inflammatory disease (N. gonorrhoeae)
symptoms as outlined in picmonic-tenosynovitis, septic arthritis etc.
How do you diagnose and treat and prevent NJI?
Diagnose: ID bacteria in the synovial fluid-difinitive
WBC count + gram stain + culture.
Treat: Early to prevent joint damage (NGA will suffer significant damage), D&I, IV antibiotics
Prevent- nongonococcal -treat UTIs, soft tissue infections in a timely manner.
Gonococcal safe sex.
How would you determine that the synovial fluid you obtained was + for sepsis?
Vol- often >3.5 clarity- opaque color- yellow-green Viscosity- variable WBC/mm3- 15,000--->100,000 PMNs- > or = 75% Culture- often + (Nongonococcal is + 70-90% of the time)
What are the symptoms of a PJI? How do you diagnose it?
sudden local pain, and mechanical joint failure.
Diagnose- intraoperative swab cultures or sonication of joint to collect specimen from a biofilm. Sonication will provide more culturable bacteria.
Whats the most commonly reported vector borne illness in the US?
lyme disease.
In lyme disease which animals serve as reservoir, and vectors, which are not reservoirs, and which are accidental hosts?
Reservoir-white footed mouse (b/c it doesn’t clear the bsacteria)
Vectors-deer tick ixodes-primarily the small nymph
Not reservoirs-deer (can clear bacteria from immune system)
Accidental hosts- humans
What are some unique features of B. burgdorferi not listed in the picmonic description?
microaeophile
many plasmids
highly motile-axial filaments
What are the three stages of lyme disease?
3 stages: Early localized (days to 1 month)- Rash. Made on clinical grounds alone if they live, or have recently traveled to an endemic area (no serology).
Early disseminated (wks- months)-skin, heart, CNS Late (months-yrs) chronic arthritis =lyme arthritis diagnosis-based on clinical +serology. ELISA + Western with 5 bands.
Lyme arthritis-doesn’t usually have associated symptoms, most common in large joints esp knee. Usually self resolving even without treatment. Less inflammatory than NJI or PJI.
These stages can overlap, can have late symptoms without early. Put symptom with classic stage
Also the characteristic rash doesn’t need to have central clearing
