Penicillin tolerance in beta-streptococci isolated from patients with tonsillitis.

Beta-streptococci isolated from patients with acute tonsillitis were tested for penicillin tolerance defined as an MBC/MIC ratio greater than or equal to 16. 11/18 strains recovered from patients with clinical treatment failure were tolerant to penicillin in comparison with 0/15 strains from successfully treated patients. The MBC/MIC ratio was less than 16 for all strains versus cefadroxil but above that ratio for many strains versus clindamycin, doxycycline and erythromycin. We suggest that penicillin tolerance may be one reason to treatment failures in individuals with streptococcal tonsillitis and that other antibiotics could be used to treat these patients since penicillin tolerance is not correlated to a general increase in antibiotic resistance.