Fig. 3: The effect of erythromycin-based induction on erm(T) transcription.

RT-qPCR was performed on RNA isolated from log-phase cultures. a Time- and concentration-dependent changes in erm(T) mRNA transcripts in an iMLS_B isolate after exposure to erythromycin. Fold-change is shown relative to erm(T) transcription from an untreated sample for the same isolate. b Exposure-dependent fold-change in erm(T) transcripts for an iMLS_B isolate. The level of erm(T) transcripts in an iMLS_B emm92 isolate relative to the susceptible M1 control strain is shown after exposure to erythromycin (black squares). Statistical significance is shown for the T0.5 (p = 0.0045) sample compared to T0, as determined using unpaired t-tests with Welch’s correction. Changes in erm(T) mRNA levels after induction are shown relative to an untreated iMLS_B sample (blue dotted line), a Brown–Forsythe ANOVA test (p = 0.001) was used to assess differences in erm(T) transcription across the T0.5, T1, and T24 time points. c The number of erm(T) transcripts for iMLS_B and cMLS_B emm92-type isolates are shown relative to the M1 strain. Statistical significance between the iMLS_B versus cMLS_B erm(T) mRNA levels was determined using unpaired t-tests with Welch’s correction. d Fold-change in erm(T) transcripts from cMLS_B isolates after erythromycin exposure. Changes in erm(T) expression compared to the M1 strain are shown by the black squares. The fold-change in erm(T) transcripts after exposure to erythromycin for 30 min is shown relative to the untreated sample (T0) for each isolate (blue circles). For all data, RNA was isolated from three independent experiments; RT-qPCR reactions were performed in triplicate wells per sample, and results were normalized to the tuf(A) reference gene. Standard deviation was determined by the averaged log₂ ΔΔCT values for each biological replicate. GraphPad Prism software was used for statistical analysis and figure generation.