ch 47 Osteomyelitis

Question 1

biofilm

Answer 1

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

Question 2

involucrum

Answer 2

area of live encasing bone surrounded by dead bone within a compromised soft tissue envelope

Question 3

sequestrum

Answer 3

non-viable piece of bone which has lost its blood supply

Question 4

what does a sequestrum look like on radiographs

Answer 4

sharply marginated sclerotic piece of bone surrounded by radiolucent zone

Question 5

what is the most common cause of osteomyelitis in dogs and cats

Answer 5

Staphylococcus spp (60%)
E. coli
streptococcus

Question 6

what percentage of osteomyelitis cases are polymicrobial

Answer 6

42%

Question 7

what percent of osteomyelitis cases were anaerobic in the 1992 paper by Muir et al

Answer 7

64%

Question 8

what is the general pathophysiology behind osteomyelitis

Answer 8

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

Question 9

why does the ischemic injury allow growth of microorganisms

Answer 9

abx and inflammatory cells cannot reach the avascular area

Question 10

what is positively correlated to the aggressiveness of the infection

Answer 10

degree of periostitis

Question 11

describe the ischemic bone structure at its periphery

Answer 11

reactive hyperemia along the edge of bone → ↑ osteoclastic resorption and localized osteoporosis

Question 12

describe characteristics of a less aggressive bone infection

Answer 12

Less aggressive → slow separation of periosteum from bone → thickening of the cortex

Question 13

describe a more aggressive case of osteomyelitis

Answer 13

More aggressive → lamellar changes where bone are laid down in adjacent to one another (spiculated) perpendicular to the cortex

Question 14

what determines if infection develops in cases of post-traumatic osteomyelitis

Answer 14

presence of virulence characteristics (production of toxins, different adhesins), antimicrobial sensitivity, and propensity to form biofilm.

Question 15

what is meant by the extracellular environment within biofilm affects antimicrobial activity

Answer 15

Changes in hydration,
elevation in partial pressure of CO2
decreased partial pressure of O2
Lower pH

Question 16

how does bacterial adhesion occur (implant associated infection)

Answer 16

bacterial adhesion can occur via fibronectin within the conditioning film and bacterial adhesins

Question 17

what are the 3 components of any biofilm

Answer 17

1. offending microbe
2. microbe-produced glycocalyx
3. host biomaterial surface

Question 18

Quorum sensing

Answer 18

Ability of bacteria to coordinate gene expression based on population density, and the role of secreted signal molecules (autoinducers)

Question 19

exopolysaccharides

Answer 19

bacterial glycocalyx; impedes perfusion of potential antimicrobial substances to cellular targets in addition to providing substrate to replicate in

Question 20

how does bacterial biofilm promote resistance to medical management

Answer 20

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

Question 21

Unlike other species, dogs and cats lack ______ vasculature at birth, thus infections generally localized to ________ rather than crossing into _______

Answer 21

Unlike other species, dogs and cats lack TRANSPHYSEAL vasculature at birth, thus infections generally localized to METAPHYSIS rather than crossing into EPIPHYSIS

Question 22

what are the 4 main stages of biofilm formation

Answer 22

Reversible attachment
Irreversible attachment
Growth and differentiation
Dissemination (or detachment)

Question 23

what is the gold standard for diagnosis of post-traumatic osteomyelitits

Answer 23

positive bacterial culture

Question 24

radiographic appearance of hematogenous osteomyelitis

Answer 24

Polyostotic lesion in the metaphyseal regions of long bones +/- bone resorption, lysis, or periosteal reaction

Question 25

treatment for acute osteomyelitits

Answer 25

Antibiotics should be given IV for a minimum of 3-5 days followed by oral therapy for a minimum of 4-6 weeks with many cases requiring 8 weeks of therapy

Question 26

Empiric antibiotic recommendation for:
staphylococcus coagulase negative

Answer 26

1st generation cephalosporin

Question 27

Empiric antibiotic recommendation for:
staphylococcus coagulase positive

Answer 27

1st generation cephalosporin, amoxicillin-clavulanate, fluoroquinolone, chloramphenicol, TMS

Question 28

Empiric antibiotic recommendation for:
staphylococcus pseudintermedius

Answer 28

Amoxicillin-clavulanate
1st generation cephalosporin
oxacillin

Question 29

Empiric antibiotic recommendation for:
Actinomyces

Answer 29

Penicillin

Question 30

Empiric antibiotic recommendation for:
Proteus, pseudomonas, or E. coli

Answer 30

fluoroquinolone
aminoglycoside
2nd or 3rd generation cephalosporin
imipenem

Question 31

Empiric antibiotic recommendation for:
anaerobes

Answer 31

amoxicillin-clavulanate
clindamycin
metronidazole
penicillin

Question 32

Empiric antibiotic recommendation for:
blastomyces or coccidiodes

Answer 32

itraconazole
ketoconazole
amphotericin B