Joint Infections

Question 0

Staphylococcus epidermidis

Answer 0

-Gr+ cocci (clusters)
-skin, MM
-catalase+, coagulase-
Lab
-grows on MSA agar, doesn’t ferment mannitol
-Gamma hemolysis (no rxn)
Virulence
-slime layer
-adhesins=collagen, fibrinogen, elstin
-lipases, proteases
-*biofilms
Path
-cause septic arthritis through delayed PJI (3mo-2yrs)
-common cause of HAI

Question 1

Staphylococcus aureus

Answer 1

-Gr+ cocci (clusters)
-fac. anaerobe
-nares, skin, MM, throat, perineum, vagina
-loose slime layer, capsule, nonmotile, nonendospore
-coagualse-, catalse+
-forms pus
Labs
-High salt mannitol salt agar (ferments mannitol)
-Beta hemolysis (true hemolysis)
Virulence
-Protein A=binds to Fc of IgG, antiphagocytic effect
-cytolytic exotoxins- PVL
-enzymes=lipase, nuclease, protease, coagulase
-*fibronectin-binding protein=promotes binding to mucosal cells and tissue matrices
Pathology
-cause septic arthritis, most common for NJI for all age groups (nongonococcal), and early PJI (first 3 months after surgery)

Question 2

Eikenella corrodens

Answer 2

-Gr- rod
-in mouth, GU, bowels
-human bite and clenched fist injury infections
-fac. anaerobe
Lab
-fastidious
-blood, chocolate agar
-some can pit agar, produce bleach-like odor
Path
-can cause septic arthritis

Question 3

Kingella kingae

Answer 3

-Gr- coccobacillus
-oropharynx, mostly kids
-fac. anaerobe
-oxidase+
Virulence
-low virulence
-pili
-beta homolysin=causes cell lysis
Path
-leading cause septic arthritis, osteomyelitis in <4 yo
-damage to respiratory mucosa facilitates invasion of bloodstream

Question 4

Neisseria gonorrhoeae

Answer 4

-Gr- diplococci
-genital tract
-oxidase+, oxidizes glucose
Lab
-very fastidious
-chocolate or thayer martin (+antibiotics)
Virulence
-IgA1 protease
-fac. intracellular
-Opa’s, pili, and Lipooligosaccharides (LOS-binds host sialic acid)
-*outer-membrane blebbing
Path
-cause septic arthritis through hematogenous NJI and disseminated gonoccal infection (DGI)
-those sexually active (15-24)

Question 5

Borrelia burgdorferi

Answer 5

-Gr- spirochete
-microaerophile
-many plasmids (40% of total DNA)
Lab
-fastidious and slow
Virulence
-very motile=axial filaments
Path
-cause of Lyme disease
-can cause septic arthritis, hematogenous NJI