ch 47 Osteomyelitis Flashcards
(32 cards)
biofilm
microbially sessile community characterized by:
Cells which are irreversibly attached to a substrate or interface within each other
Embedded in matrix of extracellular polymeric substances that have produced and exhibited altered phenotype
involucrum
area of live encasing bone surrounded by dead bone within a compromised soft tissue envelope
sequestrum
non-viable piece of bone which has lost its blood supply
what does a sequestrum look like on radiographs
sharply marginated sclerotic piece of bone surrounded by radiolucent zone
what is the most common cause of osteomyelitis in dogs and cats
Staphylococcus spp (60%)
E. coli
streptococcus
what percentage of osteomyelitis cases are polymicrobial
42%
what percent of osteomyelitis cases were anaerobic in the 1992 paper by Muir et al
64%
what is the general pathophysiology behind osteomyelitis
Altered local concentrations of cytokines and growth factors are noted during infection → death of osteoclasts and osteoblasts → necrosis and resorption of bone matrix → ischemia → ↑ propensity for sequestra and protected growth of microorganisms
why does the ischemic injury allow growth of microorganisms
abx and inflammatory cells cannot reach the avascular area
what is positively correlated to the aggressiveness of the infection
degree of periostitis
describe the ischemic bone structure at its periphery
reactive hyperemia along the edge of bone → ↑ osteoclastic resorption and localized osteoporosis
describe characteristics of a less aggressive bone infection
Less aggressive → slow separation of periosteum from bone → thickening of the cortex
describe a more aggressive case of osteomyelitis
More aggressive → lamellar changes where bone are laid down in adjacent to one another (spiculated) perpendicular to the cortex
what determines if infection develops in cases of post-traumatic osteomyelitis
presence of virulence characteristics (production of toxins, different adhesins), antimicrobial sensitivity, and propensity to form biofilm.
what is meant by the extracellular environment within biofilm affects antimicrobial activity
Changes in hydration,
elevation in partial pressure of CO2
decreased partial pressure of O2
Lower pH
how does bacterial adhesion occur (implant associated infection)
bacterial adhesion can occur via fibronectin within the conditioning film and bacterial adhesins
what are the 3 components of any biofilm
- offending microbe
- microbe-produced glycocalyx
- host biomaterial surface
Quorum sensing
Ability of bacteria to coordinate gene expression based on population density, and the role of secreted signal molecules (autoinducers)
exopolysaccharides
bacterial glycocalyx; impedes perfusion of potential antimicrobial substances to cellular targets in addition to providing substrate to replicate in
how does bacterial biofilm promote resistance to medical management
The biofilm acts as a molecular filter;
glycocalyx impedes perfusion of the potential antimicrobial substance to cellular targets
Slow to nonexistent growth renders antibiotics ineffective since the mechanism of action of many antibiotics is based on interference with bacterial growth and reproduction
The harshness of the microenvironment of the biofilm—including lowering pH, increasing PCO2, and decreasing PO2 and hydration levels—adversely affects the activity of antimicrobial agents
Unlike other species, dogs and cats lack ______ vasculature at birth, thus infections generally localized to ________ rather than crossing into _______
Unlike other species, dogs and cats lack TRANSPHYSEAL vasculature at birth, thus infections generally localized to METAPHYSIS rather than crossing into EPIPHYSIS
what are the 4 main stages of biofilm formation
Reversible attachment
Irreversible attachment
Growth and differentiation
Dissemination (or detachment)
what is the gold standard for diagnosis of post-traumatic osteomyelitits
positive bacterial culture
radiographic appearance of hematogenous osteomyelitis
Polyostotic lesion in the metaphyseal regions of long bones +/- bone resorption, lysis, or periosteal reaction
