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Questions and Answers
Which type of infection is a common cause of osteomyelitis?
Which type of infection is a common cause of osteomyelitis?
- Salmonella spp
- Neisseria gonorrhoeae
- Brucella species
- Staphylococcus aureus (correct)
Which of the following is a LESS common cause of osteomyelitis?
Which of the following is a LESS common cause of osteomyelitis?
- Enterobacteriaceae
- Streptococci
- Pseudomonas aeruginosa
- Brucella species (correct)
What laboratory test is most useful for diagnosing septic arthritis?
What laboratory test is most useful for diagnosing septic arthritis?
- Bone biopsy
- MRI scan
- Synovial fluid evaluation (correct)
- Blood culture
Which pathogen is a common cause of both osteomyelitis and septic arthritis?
Which pathogen is a common cause of both osteomyelitis and septic arthritis?
What factor allows Staph. epidermidis to be a cause of infections on prosthetic devices?
What factor allows Staph. epidermidis to be a cause of infections on prosthetic devices?
Which membrane-damaging toxin produced by Staph. aureus is the most potent?
Which membrane-damaging toxin produced by Staph. aureus is the most potent?
What characteristic differentiates staphylococci from streptococci?
What characteristic differentiates staphylococci from streptococci?
What primary function does Protein A serve in Staph. aureus?
What primary function does Protein A serve in Staph. aureus?
Which toxin is primarily responsible for Toxic Shock Syndrome?
Which toxin is primarily responsible for Toxic Shock Syndrome?
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Study Notes
Osteomyelitis
- Inflammatory condition of bone and/or bone marrow, usually caused by bacterial or fungal infection
- Can result from:
- Hematogenous source: infection through bloodstream from a distant site
- Contiguous source: extension from an adjacent local infection
- Direct inoculation following trauma
Causes of Osteomyelitis
- Common causes:
- Staphylococcus aureus (most common)
- Coagulase-negative staphylococci (S. epidermidis, etc.)
- Streptococci/Enterococci
- Pseudomonas aeruginosa
- Enterobacteriaceae (E. coli, Proteus, etc.)
- Anaerobic bacteria (Bacteroides, etc.)
- Mycobacterium tuberculosis
- Less common causes:
- Brucella species
- Aspergillus and Candida spp
- Salmonella spp
Infectious Arthritis
- Infection of one or more joints caused by bacteria, viruses, fungi, and parasites
- Causative organisms:
- Staphylococcus aureus (most common)
- Streptococcus pyogenes
- Streptococcus pneumoniae
- Hemophilus influenzae
- Neisseria gonorrhoeae
- Brucella species
- Salmonella species
- Neisseria meningitidis
- Mycobacterium tuberculosis
- Bacteroides species
- Pasteurella multocida
Laboratory Diagnosis
- Evaluation of synovial fluid from the affected joint is the most useful diagnostic test
- Tests include culture, Gram stain, crystals analysis, and white blood cell count with differential
Staphylococcus
- Genus Staphylococcus has at least 30 species
- Coagulase-positive Staph. aureus and coagulase-negative Staph. epidermidis and Staph. saprophyticus
Staphylococcus aureus
- Gram-positive cocci arranged in grape-like irregular clusters
- Non-motile and do not form spores
- Virulence factors:
- Cell surface adhesins (e.g. fibronectin-binding protein, collagen-binding protein, clumping factor)
- Enzymes (e.g. catalase, coagulase)
- Exotoxins (e.g. α-, β-, γ-, and δ-hemolysins, P-V leukocidin)
- Capsule protects the bacteria by inhibiting phagocytosis
Virulence Factors of Staphylococcus aureus
- Membrane-damaging toxins:
- α-toxin is the most potent membrane-damaging toxin
- Enterotoxins:
- 15 enterotoxins (A-E and G-P)
- Responsible for staphylococcal food poisoning
- Very heat resistant and resist hydrolysis by GIT enzymes
- TSST-1:
- Responsible for most cases of Toxic Shock Syndrome
- Exfoliative toxin:
- Causes the scalded skin syndrome
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