Listeria monocytogenes beta-hemolysis on blood agar may be mistaken for infection with which groups of streptococci?

• A. Group A Streptococcus or Group B Streptococcus
• B. Group A Streptococcus
• C. Group B Streptococcus
• D. Streptococcus pneumoniae or Streptococcus mitis

Answer: (A)

Beta-hemolysis on blood agar can be produced by different organisms, and Listeria monocytogenes can mimic the appearance of beta-hemolytic streptococci. Among streptococci, the groups that routinely show complete (beta) hemolysis are Group A and Group B. Because Listeria is a small gram-positive rod that also creates a clear zone around colonies, it can be mistaken for infection with either Group A or Group B streptococci when relying on hemolysis pattern alone. Distinguish them with additional tests: Listeria is catalase positive and shows characteristic motility at room temperature (tumbling), whereas streptococci are catalase negative. This helps prevent misidentification despite the overlapping hemolysis.