Common Organisms in Osteomyelitis
Staphylococcus aureus is the most common pathogen in osteomyelitis, found in approximately 50% of cases, followed by coagulase-negative staphylococci (25%), aerobic streptococci (30%), and Enterobacteriaceae (40%). 1
Microbiology by Type of Osteomyelitis
Pressure Injury-Related Osteomyelitis
- Polymicrobial infections are common, with an average of 3 aerobes and 1 anaerobe isolated from a single wound 1
- S. aureus is the predominant organism (77.1%), followed by Peptostreptococcus spp. (48.6%) and Bacteroides spp. (40%) 1
- Pseudomonas aeruginosa and Enterococcus species are also frequently isolated 1
- Approximately 30% of cultures are polymicrobial 1
Diabetic Foot Osteomyelitis
- Many cases are monomicrobial, but most are polymicrobial 1
- S. aureus is the most commonly isolated pathogen (found in ~50% of cases) 1
- Coagulase-negative staphylococci (
25%), aerobic streptococci (30%), and Enterobacteriaceae (~40%) are other frequent isolates 1 - Bone infection typically develops by contiguous spread from overlying soft tissue 1
Native Vertebral Osteomyelitis
- S. aureus, streptococcal species, enteric bacteria, and other gram-negative rods are the most common pathogens 1
- In endemic regions, Mycobacterium tuberculosis and Brucella species are common causative agents 1
- Fungal pathogens account for only 0.5%-1.6% of cases, primarily in immunocompromised patients 1
Pediatric Osteomyelitis
- S. aureus is the most common pathogen across all pediatric patients 1
- Group B streptococcus is common in neonates 1, 2
- Kingella kingae is common in children under 4 years of age 1, 2
- Salmonella species are common in patients with sickle cell disease 1, 2
Microbiology by Route of Infection
Hematogenous Osteomyelitis
- S. aureus is the predominant pathogen 3, 4
- Fusobacterium species are commonly found in hematogenous long bone infections 5
- Hematogenous spread can produce polymicrobial disease in 13% of cases 6
Contiguous Spread Osteomyelitis
- Polymicrobial infections are common (59% of cases) 6
- Bacteroides fragilis group is commonly found in hand and feet infections 5
- Pigmented Prevotella and Porphyromonas species are mostly isolated in skull and bite infections 5
Special Considerations
Chronic vs. Acute Osteomyelitis
- 5% of patients with acute osteomyelitis have polymicrobial infections 6
- 30%-60% of patients with chronic osteomyelitis have polymicrobial infections 6
- The number of isolates per case is similar for acute (3.2) and chronic (3.1) forms 6
Antibiotic Resistance Concerns
- In some settings, 85% of S. aureus isolates from pressure injuries are methicillin-resistant 1
- 21.6% of gram-negative isolates may be multidrug-resistant, predominantly P. aeruginosa and Acinetobacter species 1
- S. aureus can form small colony variants and biofilms, contributing to persistent infections 3
Anatomical Distribution
- Polymicrobial osteomyelitis most commonly affects bones of the skull, face, and feet 6
- In pressure injury-related osteomyelitis, the pelvis is commonly involved 1
- In diabetic foot osteomyelitis, the forefoot is most commonly involved 1
Diagnostic Considerations
- Blood cultures are positive in only a minority of cases but may reveal anaerobes in acutely ill patients 1
- Bone biopsy is the gold standard for diagnosis and should be obtained when possible 1
- Soft tissue or sinus tract specimens do not accurately reflect bone culture results and should not be used for selecting antibiotic therapy 1