A child presents with skin lesions of the leg showing gram-positive cocci in chains and beta-hemolytic colonies. Which test best identifies this pathogen ?
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Answer: C. Bacitracin sensitivity
Explanation
Beta-hemolytic streptococci in chains are definitively identified and differentiated by sensitivity to bacitracin. Streptococcus pyogenes exhibits high susceptibility to bacitracin disks in laboratory screening tests. Option C provides the exact diagnostic test required to distinguish this specific bacterial pathogen correctly. Gram-positive cocci growing in chains frequently indicate streptococcal species infections in clinical specimens. Beta-hemolysis refers to complete lysis of red blood cells surrounding colonies on blood agar plates. Laboratory microbiology uses differential disc diffusion tests to identify specific bacterial species rapidly.
Prompt identification of streptococcal skin infections ensures patients receive appropriate antibiotic therapy promptly. Untreated streptococcal infections can lead to severe systemic complications like rheumatic fever or glomerulonephritis. Diagnostic microbiology laboratories rely on standard biochemical tests to guide effective clinical treatments. Bile solubility testing is used primarily to differentiate Streptococcus pneumoniae from other alpha-hemolytic streptococci. Optochin sensitivity is the standard laboratory test for identifying Streptococcus pneumoniae bacterial isolates. Catalase testing differentiates staphylococci from streptococci since staphylococci are catalase-positive.
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