FIG 3.

Spontaneous resistance mutation frequency of S. pneumoniae for trimethoprim and deoxycholic acid. Bacterial suspensions prepared with fresh cultures of S. pneumoniae strain EF3030 or TIGR4 were adjusted to a density of ∼10⁸, ∼10⁹, ∼10¹⁰, ∼10¹¹, and ∼10¹² CFU/ml and inoculated onto blood agar plates (BAP) containing trimethoprim (Tmp, 1 μg/ml) or deoxycholic acid (DoC, 0.5 mg/ml). Each inoculum was further diluted and plated onto plain BAP. All cultures were incubated for 20 h, after which bacteria were counted. The spontaneous mutation frequency (smF) was calculated by dividing the number of spontaneously resistant pneumococci, i.e., grown on BAP with trimethoprim or DoC, by the bacterial population. Error bars represent the standard errors of the means calculated using data from at least three independent experiments. The median smF is shown on each bar.