—Drs Kaplan and Amren find it surprising that our data make the point that "the single culture is not good enough, despite more than three decades of experience showing just the opposite."We have, for 8 years, used two plates, blood agar incubated aerobically (5% to 10% carbon dioxide to enhance recovery of group C streptococci) and blood agar with trimethoprim-sulfamethoxazole (TMP-SMX) incubated anaerobically. Based on the work of others, we expected this to be more sensitive and found it to be so. Viridans streptococci suppress group A β-hemolytic streptococci (GABHS), reportedly mediated by bacteriocins.1 With appropriate thymidine concentration,2 TMP-SMX agar inhibits viridans streptococci. In anaerobic incubation, added TMP-SMX inhibits commensal β-hemolytic anaerobes. We were influenced by Gunn et al,3 who reported that in 6200 cultures aerobic TMP-SMX recovered nearly twice as many GABHS as did plain blood agar (593 vs 338). We were also
Schrantz RD, Wegner DL, Witte DL. Diagnosing Streptococcal Pharyngitis-Reply. JAMA. 1992;268(5):599–600. doi:10.1001/jama.1992.03490050047009
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