Microbiology

Question 1

What is septic arthritis?

Answer 1

Infection of joint space

Question 2

List 3 ways that pathogens can be introduced into the joint

Answer 2

Haematogenous from distant focus of infection
Contiguous from infected bone
Direct inoculation from trauma/injection

Question 3

Which 2 organisms usually cause septic arthritis?

Answer 3

Staph aureus

Streptococci

Question 4

Name 2 rare causes of septic arthritis

Answer 4

H. influenza

N. gonorrhoea

Question 5

How is septic arthritis diagnosed?

Answer 5

BLOOD CULTURE
Joint aspirate for M C&S
Ultrasound

Question 6

What is the empirical treatment for septic arthritis?

Answer 6

IV Flucloxacillin

Question 7

How is a patient

Answer 7

IV Flucloxacillin + Ceftriaxone

Question 8

What is osteomyelitis?

Answer 8

Inflammation of bone and medullary cavity

Usu long bones/verterbrae

Question 9

List 2 causes of acute osteomyelitis

Answer 9

Staph aureus

Streptococci

Question 10

List 5 causes of chronic osteomyelitis

Answer 10

M. tuberculosis
P. aeruginosa
Salmonella (esp sickle cell pts)
Brucella
Coliforms

Question 11

List 4 ways that osteomyelitis can be spread

Answer 11

Haematogenous
Contiguous
Via prostheses
Associated with peripheral vascular disease

Question 12

State 4 risk factors associated with developing infection in prosthetic joints

Answer 12

Rheumatoid arthritis
Diabetes
Malnutrition
Obesity

Question 13

State 3 types of implant infections, and their timescales

Answer 13

Early post-op: 0-3 months
Delayed: 3-24 months
Late: >24 months

Question 14

Where in the body can coagulase -ve staph (CoNS) be found?

Answer 14

Skin - commensals

• low virulence
• produces biofilm

Question 15

How is a diagnosis of PJI made?

Answer 15

Multiple bacterial cultures

- from tissue and bone

Question 16

How is PJI treated?

Answer 16

Ideally remove implant and cement

6wks antibiotic treatment before re-implantation

Question 17

What is necrotising fasciitis?

Answer 17

Acute severe infection of subcutaneous soft tissue
Crosses tissue plains
Rapidly progresses to mortality

Question 18

How does necrotising fasciitis present?

Answer 18

Exceptionally painful
Skin looks fairly normal
Systemic toxicity

Question 19

How many types of necrotising fasciitis are there?

Answer 19

2

Question 20

What is type I necrotising fasciitis?

Answer 20

Anaerobes
+ other bacteria
“synergistic gangrene”

Question 21

What is type II necrotising fasciitis>

Answer 21

Group A strep

affects young and otherwise well people

Question 22

How is necrotising fasciitis diagnosed?

Answer 22

Observation - pain disproportionate to physical appearance

Swabs and biopsy for M C & S

Question 23

How is necrotising fasciitis treated?

Answer 23

Surgical debridement

Strep pyogenes: penicillin + clindamycin

Question 24

What is gas gangrene?

Answer 24

Rapidly spreading gangrene caused by soil bacteria that emits malodorous gas

Question 25

Which organism is most associated with gas gangrene?

Answer 25

Clostridium perfringens | - strictly gram +ve anaerobic rods

Question 26

What is the most important feature of the bacteria that cause gas gangrene?

Answer 26

They produce spores

Question 27

How does gas gangrene brew?

Answer 27

Spores germinate in otherwise unhealthy cells | Leads to accumulation of gas in tissues - 'crepitus'

Question 28

What is the treatment for gas gangrene?

Answer 28

Urgent surgical debridement IV Penicillin +/- Metronidazole Oxygen

Question 29

What is tetanus?

Answer 29

Bacterial infection causing contraction and spasm of voluntary muscles

Question 30

Which bacterium is responsible for tetanus?

Answer 30

Clostridium tetani | - found in soil, animal bites

Question 31

How does clostridium tetani cause the condition?

Answer 31

Neurotoxin binds to and prevents release of neurotransmitters Leads to spastic paralysis - lock jaw All toxin relateed, non invasive in tissues

Question 32

How is tetanus treated?

Answer 32

Antitoxin + penicillin + debridement (esp bite area)

Question 33

What type of vaccination is given to prevent tetanus infection?

Answer 33

Toxoid vaccine + boosters

Question 34

Which 3 antibiotics can be used to treat staph and strep PJIs?

Answer 34

Flucloxacillin Vancomycin - also diphtheriods Clindamycin - antitoxin properties

Question 35

List 3 antibiotics that can be used in PJIs caused by coliforms

Answer 35

Gentamicin Ceftriaxone Ciprofloxacin

Question 36

What is a biofilm?

Answer 36

Slime layer surrounding a group of bacteria stuck onto bone/prostheses Prevents penetration of normal doses of antibiotic treatment

Question 37

What are the 3 principles of treating a PJI with antibiotics in the presence of biofilms

Answer 37

High dose (usu IV) Long term Bacteriocidal

Question 38

What is the surgical treatment of PJIs

Answer 38

Debridement - may retain prosthesis - prosthesis removal may be in 1 or 2 stages

Question 39

Which organisms normally cause acute primary PJIs?

Answer 39

Staph aureus | Streptococci

Question 40

Which organisms normally cause chronic PJIs?

Answer 40

CoNS | Propionibacteria

Question 41

List the 3 protocol features of PJI surgery

Answer 41

No pre-op antibiotics Min 6weeks antibiotic treatment before surgery Min 3 bone samples for culture

Question 42

Which 2 antibiotics are used to treat gram positive PJIs?

Answer 42

Fluclox | Vancomycin (if penicillin resistant)

Question 43

Which 2 antibiotics are used to treat gram negative PJIs?

Answer 43

Cotrimoxazole | Amoxicillin *rare*

Question 44

List 2 standards for prophylactic antibiotic treatment for PJI surgery

Answer 44

1st dose must be given within an hour of knife-to-skin | Prophylaxis should not extend > 24hr of surgery

Question 45

Name the standard orthopaedic prophylaxis

Answer 45

1.2g coamoxiclav, peri op | + 2 post-op doses

Question 46

Which antibiotic is administered as prophylaxis if the patient is penicillin allergic?

Answer 46

Cotrimoxazole