LG 3.6 Micro Joint Infections

Question 1

3 most common organisms that cause NJI:

Answer 1

1. Staph aureus (nongonococcal) 2. Neisseria gonnrrhoeae (gonococcal) 3. Borrelia burgdorferi

Question 2

2 most common organisms causing PJI:

Answer 2

S. aureus, S. epidermidis

Question 3

IDing info for S aureus

Answer 3

o Gr+ cocci, clusters o Catalase +, Coagulase +, Mannitol fermenter, beta-hemolytic o Facultative anaerobe o Ubiquitous, normal microbiota (nares, skin, mucous membranes)

Question 4

virulence factors S aureus

Answer 4

• SCCmec chromosome → Panton-Valentine leukocidin (PVL) • Protein A • SCCmec chromosome → mecA gene • Enzymes • Fibronectin-binding protein

Question 5

ID info for Staph epidermidis

Answer 5

o Gamma-hemolysis, catalase +, coagulase -, mannitol fermentation -

Question 6

virulence factors for Staph epidermidis

Answer 6

o Slime layer o Adhesins o biofilms

Question 7

ID info for Eikenella corrodens

Answer 7

o Gr- rod - facultative anaerobe o Normal microbiota (mouth, GU, GI) (Human bite/clenched fist injury infix.) o Pit agar o Bleach-like odor

Question 8

ID info for Kingella kingae

Answer 8

o Gr- coccobacillus o Human reservoir (normal microbiota: oropharynx) mostly kids o Facultative anaerobe o Beta-hemolytic o Oxidase +

Question 9

Virulence factors K kingae

Answer 9

(Low virulence) damage to respiratory mucosa (e.g. viral) facilitates invasion bloodstream

Question 10

ID info for Neisseria gonorrhoeae (morphology and habitat only)

Answer 10

o Gr- diplococci o Human reservoir

Question 11

other ID info for Neisseria gonorrhoeae

Answer 11

• Aerobe to facultative anaerobe • Oxidase + • Catalase + • Oxidizes glucose • chocolate or Thayer-Martin (=chocolate agar + antibiotics)

Question 12

Gonococcal virulence factors (5 of them)

Answer 12

1. Adhesions (Opa, pili) 2. IgA1 protease 3. facultative intracellular 4. antigenic and phase variation (Opa, pili, LOS) 5. outer membrane blebbing

Question 13

symptoms of DGI and gonococcal arthritis

Answer 13

1. main (red) one: septic arthritis 2. also low-grade fever, petechial skin lesions migratory polyarthralgia

Question 14

nongonococcal arthritis symptoms

Answer 14

o fever, joint pain (hot, swollen), impaired range of motion • usually monoarticular o knee most common

Question 15

gonococcal arthritis symptoms

Answer 15

o DGI symptoms plus… o polyarticular (less often mono) arthritis (knee, wrist, ankle, elbow) o less joint damage than non-gonococcal arthritis

Question 16

describe the three-part diagnostic strategy for NJI

Answer 16

• I.D. bacteria in synovial fluid is definitive o WBC count + gram-stained smear + culture

Question 17

Diagnosing PJI (*not a posted objective)

Answer 17

o More difficult than NJI • less inflammation • infecting agent may be lacking in synovial fluid • biofilms not readily cultured

Question 18

explain the role of biofilms in the pathogenesis and diagnosis of PJI

Answer 18

• biofilms complicate! o resting state • smaller inflammatory response • antibiotic protection • tougher to isolate microbes

Question 19

what’s Lyme Disease vector?

Answer 19

1. blacklegged tick (‘deer tick’) Ixodes scapularis in hyperendemic regions eastern U.S 2. nymph is primary vector

Question 20

What’s Lyme Disease reservoir

Answer 20

rodent reservoir, esp. white-footed mouse

Question 21

In US, where are most reported Lyme Disease cases?

Answer 21

northeast and upper midwest US

Question 22

Describe seasonality of Lyme Disease

Answer 22

1. between 2001 - 2010, most cases by far in June/July (70 - 80K) 2. second most in August and May (30K and 20K, respectively). 3. Lyme’s is most commonly reported vectorborne illness in US

Question 23

describe interplay between deer tick, rodent, human in Lyme Disease

Answer 23

Question 24

ID factors for Borrelia burgdorferi

Answer 24

Gr- spirochete
Microaerophile

Question 25

virulence factors for burgorferi

Answer 25

very motile

(bundles of axial filaments between plasma membrane and outer membrane)

Question 26

descibe Early localized Lyme Disease

Answer 26

Tick bite –> several days to 1 month later erythema migrans = bull’s eye rash appears (80% get this)

Question 27

describe early disseminated Lyme disease

Answer 27

1. weeks to months after bite
2. at this point Lyme disseminated systemically (skin, heart, CNS, joints) 3. could have corresponding systemic symtoms

Question 28

Late Lyme symptoms

Answer 28

1. after months to years
2. usually manifests as chronic arthritis = Lyme arthritis
3. 60% untreated get this
4. occasionally with constitutional symptoms
   large joints most common (knee monoarthritis most common
   even w/out antibiotics usually resolves, but can last for years

Question 29

Not really helpful to culture Lyme. why?

Answer 29

there are few spirochetes in blood, tissues

and culture not available most clinical labs

Question 30

name and describe 2 types of immunologic (serologic) methods of diagnosis

Answer 30

1. direct

looking for presence of microbe antigens
uses known antibody

2. indirect

looking for host antibodies directed against microbe antigens
uses known antigens
current exposure, previous exposure

Question 31

titer

Answer 31

1. results of many immunologic tests expressed as titer
2. highest dilution (lowest concentration) of specimen (e.g. serum) that gives a positive reaction in test

Question 32

how is titer expressed?

Answer 32

expressed as reciprocal of highest dilution (lowest concentration)

Question 33

how does titer confirm new infection?

Answer 33

to confirm a new infection→ usually have to demonstrate either seroconversion or a rising titer→ a fourfold ↑ in a convalescent titer obtained 2-3 wks after the acute titer is considered diagnostic in most situations

Question 34

ELISA

Answer 34

1. enzyme-linked immunosorbent assay
2. uses an enzyme as label
3. reaction of the enzyme with its substrate produces a colored product → positive test
4. can detect either antibody or antigen
5. indirect more common in I.D.
6. quantitative

Question 35

Western blot procedure

Answer 35

microbial proteins separated

         ↓transferred to membrane

incubated w/ patient serum

              ↓

secondary antibody (w/ enzyme or radioactive isotope as label)

              ↓

add substrate for enzyme

              ↓

bands ‘light up’ where antibody recognizes each antigen

Question 36

How to diagnose early localized Lyme

Answer 36

made on clinical grounds alone when characteristic erythema migrans lesion present in patient who lives or has recently traveled to endemic area

Question 37

How to diagnose early dissiminated/late Lyme

Answer 37

based on clinical + serology when patient lives or has recently traveled to endemic area

Question 38

What are the 3 ways that native joint infections can occur?

Answer 38

*Hematogenous spread.

Direct inoculation (trauma, bite).

Extension of osteomyelitis.

Question 39

What is the most common infectous agent to cause early PJI, late PJI?

Answer 39

Early = Staph. Aureus, more virulent.

Late = Staph. Epidermidis, less virulent.

Question 40

When would you use a chocolate agar plate vs. a Thayer-Martin plate for ID of N. Gonorrhoeae?

Answer 40

Chocolate for fluid from joint. (nothing else should be in the joint so easy to ID alone).

Thayer-Martin for rectal, blood, throat (many other organisms here so you want to screen them out).

Question 41

Regarding PMN counts how can you tell between gonococcal and nongonococcal infiltration?

Answer 41

S. aureus large infiltration PMNs

N. gonorrhoeae smaller infiltration PMNs

Question 42

What is seroconversion?

Answer 42

Test patient serum, they don’t have it.

Check again at a later time, now they do have it.

Question 43

K kingae leading cause of _____ infx in _______ age-group.

Answer 43

septic arthritis, osteomyelitis <4 years age