What is the most common organism responsible for osteomyelitis in infants?

In infants, the most common organism responsible for osteomyelitis is Staphylococcus aureus. This bacterium is prevalent in the neonatal population and can cause a range of infections, including osteomyelitis, particularly due to its ability to colonize the skin and mucosal surfaces, as well as its pathogenic capabilities. In the context of osteomyelitis, Staphylococcus aureus can gain entry to the bone via direct spread from adjacent infections, hematogenous spread, or through traumatic injuries.

While other organisms such as Group B Streptococcus and Escherichia coli are also known to cause infections in infants, they are less commonly associated with osteomyelitis specifically. Group B Streptococcus is primarily linked with early-onset sepsis and meningitis. Escherichia coli is more frequently implicated in urinary tract infections and may contribute to sepsis but is not the dominant organism in osteomyelitis cases. Streptococcus pyogenes, although capable of causing skin and soft tissue infections, is not typically associated with osteomyelitis in infants.

Therefore, Staphylococcus aureus stands out as the most significant pathogen in this context, making it the correct answer.