Lecture 14 - Osteomyelitis Flashcards
Rheumatic fever?
migratory polyarthritis, also carditis, associated w group A strep infection
Septic arthritis?
extremely painful w movement, purulent synovial fluid
Osteomyelitis?
infection and inflammation of bone or bone marrow
Routes of bone infection?
trauma, spreading from local area of infection, haematogenous route
Pathogenesis?
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)
Risk groups?
diabetics w foot ulcers, trauma, bone surgery, joint replacements, IV drugs, root canal, skin and soft tissue infection, chicken pox in children (rare)
Pathogens?
Staph Aureus (80%), strep. pyogenes (group A), group B strep, hemophilus influenzae, enterobacter spp.
Adult locations?
vertebrae, prosthetic joint, post-trauma, diabetic foot infection
Children locations?
tibia, femur, humerus
Specific symptoms?
pain/weakness of specific bone, redness, fever
Blood sample
high WBC, bacteria presence
Screening?
Xray and CT low sensitivity but high specificity, MRI to confirm diagnosis, biopsy specific but highly invasive
Identifying and seperating gram positive cocci?
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
Staphylcoccus aureus?
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
How can S. Aureus cause skin infection?
crack in skin, splinter, hair
Virulence factors?
adhesins, immune evasion factors, spreading factors (e.g. proteases, DNAses, hyaluronidase)
Adhesins - MSCRAMMs?
microbial surface components recognising adhesive matrix molecule - recognise particular ECM protiens
Spreading factors?
staphylokinase (fibrinolysin), lipases, DNAses, cytolysis (destroy epithelial cells)
Immune evasion factors?
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)
Superantigens?
non-specific highly potent T cell mitogens, trigger strong pro-inflammatory immune response, leading to tissue destruction, vascular leakage, multiorgan failure and toxic shock
S. Aureus therapy?
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
Penicillin?
beta-lactam antibiotic, only work on gram positive (except extended spectrum penicillins e.g. amoxycillin), irreversible inhibition of transpeptidase
Resistance to beta-lactam antibiotics>
beta-lactamases e.g. penicillase, transferrable between bacterial strains and species
Beta-lactam resistant penicillins?
oxacillin, flucoxacillin, OR use penicillin combined with beta-lactamase inhibitor e.g. clavulanic acid
Impetigo?
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)
Folliculitis?
pyogenic infection of hair follicles, raised hair, pus beneath epidermal surface
Furuncle?
extension of folliculitis, large painful raised cutaneous nodules (pus)
Carbuncle?
coalescence of furuncles, progress into deeper tissue, systemic symptoms (fever, chills)
Cellulitis?
pyogenic inflammation, usually around trama site, old age, immune deficient and diabetic ulcers are risk factors, oral or iv antibiotic treatment e.g. augmentin
Necortising pneumonia?
severe form of bacterial pneumonia caused by S. Aureus
Bacterial pneumonia?
invasion of alveoli, abscess formation (cytolytic toxins), Strep. pneumonia most common but also s. aureus cause
