Importantly, even though no antibiotic selection was applied in
the agar plates, we observed a low number of 8325-SR colonies
resistant to tetracycline throughout the experiment, indicating
that the tetK marker initially located on a USA300-borne plasmid
was transferred to and maintained in 8325-SR without antibiotic
selection (Fig. 3a).
To assess the impact of autotransduction during antibiotic
selection, we co-cultured the erythromycin-sensitive lysogen
8325-SR together with the erythromycin-resistant 8325-4 chrom
(Fig. 3b) or USA300 (Fig. 3c) in the presence of increasing
concentrations of erythromycin. Even at antibiotic concentrations
lethal to 8325-SR, erythromycin-resistant 8325-SR transductants
emerged in the co-cultures, while the original lysogenic population
gradually declined with increasing antibiotic concentrations.
This effect was abolished by citrate. These data show that