Fig. 3

Determination of rates of excisants and presence of circular forms of SCCmec during growth of MRSA N315 various growth conditions. a In a first series of experiments, bacteria were grown at 37 °C in TSB (continuous line), but inoculated with either a 1/100 or a 1/10,000 dilutions of an overnight culture. Open columns represent the rates of excisants following inoculation with the 1/100 dilution and grey columns represent the rates of excisants following inoculation with the 1/10,000 dilution. In a second series of experiments oxacillin (final concentration of 4 mg/L) was added at the time of inoculation and both growth (dotted line) and rates of excisants (black column) were followed over time. Asterisks indicate that measurements were below the limit of detection. Error bars represent the average ± SD of three independent measurements performed in three independent cultures. b Presence of closed circular SCCmec during growth in TSB was detected by endpoint PCR using 200 or 500 ng of DNA previously used as template for qPCR. Circular SCCmec could not be quantified by qPCR because it remained below detection limits