Common Organisms in Osteomyelitis

Microbiology by Type of 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, 2
• In pressure injury-related osteomyelitis, polymicrobial infections are common, with an average of 3 aerobes and 1 anaerobe isolated from a single wound 2
• S. aureus is the predominant organism (77.1%) in pressure injury-related osteomyelitis, followed by Peptostreptococcus spp. (48.6%) and Bacteroides spp. (40%) 2
• In diabetic foot osteomyelitis, 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 in diabetic foot osteomyelitis 1
• Bone infection typically develops by contiguous spread from overlying soft tissue in diabetic foot osteomyelitis 1
• In native vertebral osteomyelitis, S. aureus, streptococcal species, enteric bacteria, and other gram-negative rods are the most common pathogens 3
• In endemic regions, Mycobacterium tuberculosis and Brucella species are common causative agents of native vertebral osteomyelitis 3, 4
• Fungal pathogens account for only 0.5%-1.6% of cases of native vertebral osteomyelitis, primarily in immunocompromised patients 4
• In pediatric osteomyelitis, S. aureus is the most common pathogen across all pediatric patients 5
• Group B streptococcus is common in neonates with osteomyelitis 5, 6
• Kingella kingae is common in children under 4 years of age with osteomyelitis 5, 6
• Salmonella species are common in patients with sickle cell disease and osteomyelitis 5, 6

Microbiology by Route of Infection

Special Considerations

• In some settings, 85% of S. aureus isolates from pressure injuries are methicillin-resistant 2
• 21.6% of gram-negative isolates may be multidrug-resistant, predominantly P. aeruginosa and Acinetobacter species 2
• In pressure injury-related osteomyelitis, the pelvis is commonly involved 2
• 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 2
• 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 7