Determination of in vitro postantibiotic effects in Staphylococcus aureus and Escherichia coli by [3H]thymidine incorporation.

Postantibiotic effects (PAE) and control-related effective regrowth time (CERT) of dicloxacillin, vancomycin, rifampin and gentamicin in Staphylococcus aureus and imipenem, gentamicin, tobramycin, doxycycline and rifampin in Escherichia coli were measured by standard viability counting and [3H]thymidine incorporation. For PAE determination, the two methods correlated well; r2=0.821 for S. aureus and r2=0.939 for E. coli. For viable counts below the detection limits of 105 to 106 log10 CFU/mL, the PAE was overestimated by the [3H]thymidine method. Quantitation of CERT by both methods showed a good correlation, r2=0.867 for S. aureus and r2=0.997 for E. coli. Measuring [3H]thymidine incorporation in bacteria is a novel alternative method for the determination of PAE and CERT.