Lecture 14 - Osteomyelitis

Question 1

Rheumatic fever?

Answer 1

migratory polyarthritis, also carditis, associated w group A strep infection

Question 2

Septic arthritis?

Answer 2

extremely painful w movement, purulent synovial fluid

Question 3

Osteomyelitis?

Answer 3

infection and inflammation of bone or bone marrow

Question 4

Routes of bone infection?

Answer 4

trauma, spreading from local area of infection, haematogenous route

Question 5

Pathogenesis?

Answer 5

bacteria infect bone, leukocyte infiltration, inflammation and pus formation, devascularisation, dead bone and abscess, bacteria may invade bone and avoid immune system and drugs (leading to chronic osteomyelitis), bacteria may spread to joint (septic arthritis)

Question 6

Risk groups?

Answer 6

diabetics w foot ulcers, trauma, bone surgery, joint replacements, IV drugs, root canal, skin and soft tissue infection, chicken pox in children (rare)

Question 7

Pathogens?

Answer 7

Staph Aureus (80%), strep. pyogenes (group A), group B strep, hemophilus influenzae, enterobacter spp.

Question 8

Adult locations?

Answer 8

vertebrae, prosthetic joint, post-trauma, diabetic foot infection

Question 9

Children locations?

Answer 9

tibia, femur, humerus

Question 10

Specific symptoms?

Answer 10

pain/weakness of specific bone, redness, fever

Question 11

Blood sample

Answer 11

high WBC, bacteria presence

Question 12

Screening?

Answer 12

Xray and CT low sensitivity but high specificity, MRI to confirm diagnosis, biopsy specific but highly invasive

Question 13

Identifying and seperating gram positive cocci?

Answer 13

staphylo: grape-like, strepto: chain like; catalase test (positive staph, negative strep), coagulase + is staph aureus; hemolysis alpha is s. pneumoniae, beta is s. pyogenes and gamma is enterococcus

Question 14

Staphylcoccus aureus?

Answer 14

from anterior nares or transient carriage on skin, human-human transmission, community or hospital infection, leading to skin and soft tissue disease, invasive disease, toxic shock and more

Question 15

How can S. Aureus cause skin infection?

Answer 15

crack in skin, splinter, hair

Question 16

Virulence factors?

Answer 16

adhesins, immune evasion factors, spreading factors (e.g. proteases, DNAses, hyaluronidase)

Question 17

Adhesins - MSCRAMMs?

Answer 17

microbial surface components recognising adhesive matrix molecule - recognise particular ECM protiens

Question 18

Spreading factors?

Answer 18

staphylokinase (fibrinolysin), lipases, DNAses, cytolysis (destroy epithelial cells)

Question 19

Immune evasion factors?

Answer 19

cytolysins (kill leukocytes), capsule (prevents C3b and Ig opsonisation), slime layer/extracellular polysaccharide (immune evasion antibiotic tolerance), protein A (binds IgG incorrectly @ Fc region), clumping factor (binds prothrombin and induce fibrin deposition on cell surface)

Question 20

Superantigens?

Answer 20

non-specific highly potent T cell mitogens, trigger strong pro-inflammatory immune response, leading to tissue destruction, vascular leakage, multiorgan failure and toxic shock

Question 21

S. Aureus therapy?

Answer 21

prolonged antibiotic treatment: methicillin is poisonous (30% are resistant) so use oxacillin, then vancomycin (do not use first to prevtn resistance), possible surgical removal of damaged tissue

Question 22

Penicillin?

Answer 22

beta-lactam antibiotic, only work on gram positive (except extended spectrum penicillins e.g. amoxycillin), irreversible inhibition of transpeptidase

Question 23

Resistance to beta-lactam antibiotics>

Answer 23

beta-lactamases e.g. penicillase, transferrable between bacterial strains and species

Question 24

Beta-lactam resistant penicillins?

Answer 24

oxacillin, flucoxacillin, OR use penicillin combined with beta-lactamase inhibitor e.g. clavulanic acid

Question 25

Impetigo?

Answer 25

purulent infection of derma via direct contact infection, pus filled vesicles that rupture and dry out, spread by scratching common, prevention from good hygeine, treatment with soap water and topical antibiotics (mupirocin)

Question 26

Folliculitis?

Answer 26

pyogenic infection of hair follicles, raised hair, pus beneath epidermal surface

Question 27

Furuncle?

Answer 27

extension of folliculitis, large painful raised cutaneous nodules (pus)

Question 28

Carbuncle?

Answer 28

coalescence of furuncles, progress into deeper tissue, systemic symptoms (fever, chills)

Question 29

Cellulitis?

Answer 29

pyogenic inflammation, usually around trama site, old age, immune deficient and diabetic ulcers are risk factors, oral or iv antibiotic treatment e.g. augmentin

Question 30

Necortising pneumonia?

Answer 30

severe form of bacterial pneumonia caused by S. Aureus

Question 31

Bacterial pneumonia?

Answer 31

invasion of alveoli, abscess formation (cytolytic toxins), Strep. pneumonia most common but also s. aureus cause