Microbiology Flashcards
What is another name for septic arthritis?
infectious arthritis
What is the most common way to get a native joint infection (NJI)?
hematogenous spread
Who is at highest risk for a native joint infection?
intervenous drug users
What are the two major classes of septic arthritis?
1) nongonococcal
2) gonococcal
* *both bacterial**
Which type of bacterial infection is most serious?
nongonococcal; more inflammation
What is the bacterial spectrum usually associated with native joint infections?
Gram +
What is the most common specific bacterial nongonococcal infection which leads to a native joint infection?
Staphylococcus aureus (Gram +)
What is the most common specific bacterial gonococcal infection which leads to a native joint infection?
Neisseria gonorrhoeae
Which bacterium is a leading cause of septic arthritis in children less than 4 yo?
Kingella kingae
Which bacterium’s 2nd most common manifestation is Lyme Disease?
Borrelia burgdorferi
What is the leading cause of joint infections?
prosthetic joint infections
Which bacteria comprise the most number of prosthetic joint infections and why?
1) S. aureus
2) S. epidermidis
microbiota on skin
Which tests can be done to differentiate S. aureus and S. epidermiditis?
Coagulase (S. aureus +)
Mannitol Fermentation test (S. aureus +)
How do Staphylococcus present on a slide?
Gram + cocci in clusters
What is the main virulence factor of Staphylococcus?
slime layer (and adhesins)
What is the hemolysis of Staphylococcus epidermidis?
Gamma (non-hemolytic)
How do Eikenella corrodens infections typically occur?
1) human bite
2) clenched fist injuries
What are two characteristics of Eikenella corrodens on a plate?
1) pit agar
2) bleach-like odor
What are the main virulence factors of Kingella kingae?
1) pili
2) beta hemolysis
How does Kingella kingae invade the bloodstream?
damage to respiratory mucosa (e.g. viral) facilitates invasion
When is it appropriate to use Thayer-Martin culture media?
gonococcal cultures from mouth or rectum; chocolate + selective antibiotics
What is a DGI?
Disseminated Gonococcal Infection from N. gonorrhoeae; leads to meningitis and meningococcemia
What are the main virulence factors of Neisseria?
1) adhesions (pili, Opa’s, LOS; ipo-oligosaccharides)
2) IgA protease
3) facultative intracellular
4) antigenic and phase variation with Opa’s, pili, LOS
5) bind host sialic acid to their LOS to act as decoys
6) outer-membrane blebbing
How do LOSs behave in regards to antibiotics?
Gram + (even though Neisseria are Gr- and Oxidase +)
What is the most important symptom of a disseminated gonococcal infection?
septic arthrities
What is the most common location of a nongonococcal arthritis NJI?
knee
What is the most common location of a gonoccal arthritis NJI?
polyarticular; knee, wrist, ankle, elbow
What key information comes from analyzing the synovial fluid of an NJI which help to identify the type of infection?
1) Gram-stained smear
2) WBC
3) culture
Give the following laboratory findings for septic arthritis for:
1) volume
2) clarity
3) color
4) viscosity
5) WBC per mm3
6) PMNs %
7) culture
1) volume: >3.5 mL
2) clarity: obaque
3) color: yellow to green
4) viscosity: variable
5) WBC per mm3: 15,000-100,000
6) PMNs %: >75%
7) culture: often positive
Why are nongonoccal infections more likely in the synovial fluid than in the blood?
fastidious
What unique symptoms present with a prosthetic joint infection?
1) sudden local joint pain
2) mechanical joint failure
* *no fever, swelling
What are the 2 ways to diagnose a prosthetic joint infection?
1) multiple joint biopsies
2) sonication of actual prosthetic, grow on all different conditions to identify
What special infection control technique is used when working with MRSA patients who have a prosthetic joint infection?
patient gets a pre-wash before surgery
Geographically, where is Lyme Disease most common?
Northeast, Upper Midwest
forested areas
What is the seasonality of Lyme Disease?
Peak in summer months (June-July)
Which bacterium is responsible for causing Lyme Disease?
Borrelia burgdorferi
Which vector is responsible for the transmission of Lyme Disease?
Ixodes scapularis (tick; rodent reservoir)
Which stage of development is the primary vector for the transmission of Lyme Disease?
nymph
What is beneficial about Borrelia burgdorferi having much of its DNA on plasmids?
helps manifest a variety of hosts
What is the structure, gram stain, and main virulence factor of Borrelia burgdorferi?
spirochete
Gram -
motility due to axial filaments
Is Borrelia burgdorferi typically cultured in the lab for diagnostic purposes?
No; fastidious and slow with limited metabolic capabilities; 4 week incubation period
How are Borrelia burgdorferi infections typically diagnosed?
1) titer for antibodies to the microbe
2) confirm with immunoblotting
What is the typical clinical presentation of early localized Lyme Disease?
erythema migrans (bull's eye rash) **diagnosis made on clinical grounds alone**
What is Lyme arthritis?
late Lyme Disease; chronic arthritis caused by Borrelia burgdorferi infection
What are 2 important things to remember when diagnosing Lyme Disease in addition to clinical presentation?
1) travel/activity history
2) slight increase in WBC
What are the two types of immunologic (serologic) methods of diagnosing Lyme Disease?
1) Direct: microbial antigen
2) Indirect: host antibody directed against the microbial antigen; titer
What is a titer?
quantitative measure of antibody/antigen in the body
How are titers expressed clinically?
reciprocal: last tube to give positive reaction in serial dilution (1:640) = “640”
What is a seroconversion?
patient did not have antibody the first time the titer was done (acute titer) but has antibodies now (look for 4X’s increase over time)
Is the antibody or antigen typically measured when diagnosing Lyme Disease?
antibody with ELISA; confirmed with a Western blot
early disseminated or late Lyme Disease
