Characterization of a spiramycin-inactivating macrolide esterase

EstS, a macrolide esterase, preferentially hydrolyzes spiramycin and confers protection against spiramycin and tylosin when expressed in heterologous systems, with substrate preference linked to stronger protection in Escherichia coli.

• Why it matters: Genome mining of beta-hydrolases as macrolide esterases has left resistance phenotypes incompletely explained, motivating characterization of EstS from a macrolide-resistant Streptococcus uberis report.
• What they did: The enzyme EstS was annotated and characterized as a macrolide esterase; heterologous expression tested protection, and steady-state kinetics used isothermal titration calorimetry plus high-performance chromatography coupled to mass spectrometry.
• The result: EstS hydrolyzed multiple macrolides, but only spiramycin and tylosin protection was observed, and kinetic data showed EstS prefers spiramycin, consistent with higher protection in Escherichia coli.