A gram-positive coccus from a wound culture shows B-hemolytic colonies. The most likely identification is?

The presence of beta-hemolytic colonies is a key factor in identifying the organism in question. Beta-hemolysis is characterized by the complete lysis of red blood cells in the agar surrounding the colonies, which indicates the organism is capable of producing enzymes called hemolysins that lyse red blood cells.

In this context, Streptococcus species are notable for their capacity to exhibit beta-hemolysis, particularly Streptococcus pyogenes (Group A strep) and Streptococcus agalactiae (Group B strep). This makes the identification of Streptococcus spp. in the scenario provided highly plausible.

In contrast, Staphylococcus aureus is typically associated with coagulase-positive results and is usually categorized under alpha or beta-hemolytic activity depending on the strain, but often does not present in wound cultures as predominantly beta-hemolytic. Staphylococcus epidermidis is coagulase-negative and is usually associated with skin flora and does not exhibit beta-hemolysis. Micrococcus spp. tend to be coagulase-negative and do not typically show strong hemolytic activity.

Thus, the identification of beta-hemolytic colonies indicates that a Streptococcus species