Microbiology

Question 1

What is another name for septic arthritis?

Answer 1

infectious arthritis

Question 2

What is the most common way to get a native joint infection (NJI)?

Answer 2

hematogenous spread

Question 3

Who is at highest risk for a native joint infection?

Answer 3

intervenous drug users

Question 4

What are the two major classes of septic arthritis?

Answer 4

1) nongonococcal
2) gonococcal
* *both bacterial**

Question 5

Which type of bacterial infection is most serious?

Answer 5

nongonococcal; more inflammation

Question 6

What is the bacterial spectrum usually associated with native joint infections?

Answer 6

Gram +

Question 7

What is the most common specific bacterial nongonococcal infection which leads to a native joint infection?

Answer 7

Staphylococcus aureus (Gram +)

Question 8

What is the most common specific bacterial gonococcal infection which leads to a native joint infection?

Answer 8

Neisseria gonorrhoeae

Question 9

Which bacterium is a leading cause of septic arthritis in children less than 4 yo?

Answer 9

Kingella kingae

Question 10

Which bacterium’s 2nd most common manifestation is Lyme Disease?

Answer 10

Borrelia burgdorferi

Question 11

What is the leading cause of joint infections?

Answer 11

prosthetic joint infections

Question 12

Which bacteria comprise the most number of prosthetic joint infections and why?

Answer 12

1) S. aureus
2) S. epidermidis

microbiota on skin

Question 13

Which tests can be done to differentiate S. aureus and S. epidermiditis?

Answer 13

Coagulase (S. aureus +)

Mannitol Fermentation test (S. aureus +)

Question 14

How do Staphylococcus present on a slide?

Answer 14

Gram + cocci in clusters

Question 15

What is the main virulence factor of Staphylococcus?

Answer 15

slime layer (and adhesins)

Question 16

What is the hemolysis of Staphylococcus epidermidis?

Answer 16

Gamma (non-hemolytic)

Question 17

How do Eikenella corrodens infections typically occur?

Answer 17

1) human bite

2) clenched fist injuries

Question 18

What are two characteristics of Eikenella corrodens on a plate?

Answer 18

1) pit agar

2) bleach-like odor

Question 19

What are the main virulence factors of Kingella kingae?

Answer 19

1) pili

2) beta hemolysis

Question 20

How does Kingella kingae invade the bloodstream?

Answer 20

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

Question 21

When is it appropriate to use Thayer-Martin culture media?

Answer 21

gonococcal cultures from mouth or rectum; chocolate + selective antibiotics

Question 22

What is a DGI?

Answer 22

Disseminated Gonococcal Infection from N. gonorrhoeae; leads to meningitis and meningococcemia

Question 23

What are the main virulence factors of Neisseria?

Answer 23

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

Question 24

How do LOSs behave in regards to antibiotics?

Answer 24

Gram + (even though Neisseria are Gr- and Oxidase +)

Question 25

What is the most important symptom of a disseminated gonococcal infection?

Answer 25

septic arthrities

Question 26

What is the most common location of a nongonococcal arthritis NJI?

Answer 26

knee

Question 27

What is the most common location of a gonoccal arthritis NJI?

Answer 27

polyarticular; knee, wrist, ankle, elbow

Question 28

What key information comes from analyzing the synovial fluid of an NJI which help to identify the type of infection?

Answer 28

1) Gram-stained smear 2) WBC 3) culture

Question 29

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

Answer 29

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

Question 30

Why are nongonoccal infections more likely in the synovial fluid than in the blood?

Answer 30

fastidious

Question 31

What unique symptoms present with a prosthetic joint infection?

Answer 31

1) sudden local joint pain 2) mechanical joint failure * *no fever, swelling

Question 32

What are the 2 ways to diagnose a prosthetic joint infection?

Answer 32

1) multiple joint biopsies | 2) sonication of actual prosthetic, grow on all different conditions to identify

Question 33

What special infection control technique is used when working with MRSA patients who have a prosthetic joint infection?

Answer 33

patient gets a pre-wash before surgery

Question 34

Geographically, where is Lyme Disease most common?

Answer 34

Northeast, Upper Midwest | forested areas

Question 35

What is the seasonality of Lyme Disease?

Answer 35

Peak in summer months (June-July)

Question 36

Which bacterium is responsible for causing Lyme Disease?

Answer 36

Borrelia burgdorferi

Question 37

Which vector is responsible for the transmission of Lyme Disease?

Answer 37

Ixodes scapularis (tick; rodent reservoir)

Question 38

Which stage of development is the primary vector for the transmission of Lyme Disease?

Answer 38

nymph

Question 39

What is beneficial about Borrelia burgdorferi having much of its DNA on plasmids?

Answer 39

helps manifest a variety of hosts

Question 40

What is the structure, gram stain, and main virulence factor of Borrelia burgdorferi?

Answer 40

spirochete Gram - motility due to axial filaments

Question 41

Is Borrelia burgdorferi typically cultured in the lab for diagnostic purposes?

Answer 41

No; fastidious and slow with limited metabolic capabilities; 4 week incubation period

Question 42

How are Borrelia burgdorferi infections typically diagnosed?

Answer 42

1) titer for antibodies to the microbe | 2) confirm with immunoblotting

Question 43

What is the typical clinical presentation of early localized Lyme Disease?

Answer 43

``` erythema migrans (bull's eye rash) **diagnosis made on clinical grounds alone** ```

Question 44

What is Lyme arthritis?

Answer 44

late Lyme Disease; chronic arthritis caused by Borrelia burgdorferi infection

Question 45

What are 2 important things to remember when diagnosing Lyme Disease in addition to clinical presentation?

Answer 45

1) travel/activity history | 2) slight increase in WBC

Question 46

What are the two types of immunologic (serologic) methods of diagnosing Lyme Disease?

Answer 46

1) Direct: microbial antigen | 2) Indirect: host antibody directed against the microbial antigen; titer

Question 47

What is a titer?

Answer 47

quantitative measure of antibody/antigen in the body

Question 48

How are titers expressed clinically?

Answer 48

reciprocal: last tube to give positive reaction in serial dilution (1:640) = "640"

Question 49

What is a seroconversion?

Answer 49

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)

Question 50

Is the antibody or antigen typically measured when diagnosing Lyme Disease?

Answer 50

antibody with ELISA; confirmed with a Western blot | **early disseminated or late Lyme Disease**