FIG 5.

Antibiotic pretreatment promotes GAS growth in the nasopharynx. Growth of GAS in the upper respiratory tract of antibiotic pretreated mice. (A) C57BL/6 mice were given 5,000 U penicillin intraperitoneally at the indicated intervals (−48, −24, −2, or +1 h relative to inoculation time), and 10⁸ CFU of GAS 5448 was delivered intranasally. Mice were euthanized 24 h postinoculation, and GAS CFU were quantified from nasopharyngeal lavage. (B) C57BL/6 mice were treated as described above, with uniform administration of penicillin 24 h preinfection, anti-Ly6G 24 h preinfection, or anakinra 4 h preinfection. (C) C57BL/6 mice were given penicillin 24 h preinfection and infected with 10⁸ CFU of wild-type or ΔspeB GAS 5448 as described above, and CFU were enumerated after 24 h. Data are means ± SD (n = 5 each) and are representative of at least 3 experiments. *, P < 0.05; **, P < 0.005; ns, not significant.