FIG. 2.

Dose-response curve for inhibition of sporulation by β-lactam antibiotics. An exponentially growing culture of S. griseus (A₅₀₀ = 1) in SpM was divided into 3-ml aliquots that were placed in 18- by 150-mm culture tubes containing the indicated concentration of cefoxitin (•), cefotaxime (○), or ACA (×). After incubation for an additional 4 days, the cultures were treated with ultrasound, diluted, and plated for viability. The values (in sonication-resistant units [sru] per ml) are averages ± standard deviations of duplicate experiments, each assayed in duplicate. The concentration of sonication-resistant units for each antibiotic at 0.6 μg/ml was identical to that of an untreated culture.