Inducible Mega-Mediated Macrolide Resistance Confers Heteroresistance in Streptococcus pneumoniae

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Streptococcus pneumoniae (Spn) clinical isolates often harbor the Macrolide Genetic Assembly (Mega) element.
• The Mega element encodes Mef(E) efflux pump and Mel ribosomal protection protein, conferring macrolide resistance.
• Heteroresistance, a significant challenge in clinical settings, involves a wide range of minimum inhibitory concentrations (MICs) within a bacterial population.

Purpose of the Study:

• To investigate the mechanism of macrolide heteroresistance conferred by the Mega element in Spn.
• To determine the role of Mega operon inducibility in the heteroresistance phenotype.
• To identify regulatory elements within the Mega operon responsible for induction and resistance.

Main Methods:

• Screening of Spn strains with Mega element using Etest and Population Analysis Profiling (PAP).
• Quantification of mef(E)/mel operon mRNA expression under various macrolide treatments.
• Analysis of mutant strains with deletions in the 5' regulatory region of the Mega operon.

Main Results:

• All Mega-containing Spn strains exhibited heteroresistance to 14- and 15-membered ring macrolides.
• Macrolide induction uniformly increased Mega operon mRNA expression and eliminated heteroresistance.
• A deletion in the 5' regulatory region abolished induction and heteroresistance, highlighting the role of the mef(E)L leader peptide.

Conclusions:

• Macrolide inducibility of the Mega element is directly linked to heteroresistance in Spn.
• Stochastic variation in mef(E)/mel expression within a population underlies the heteroresistance phenotype.
• Understanding this mechanism is crucial for accurate clinical resistance screening and effective antibiotic treatment strategies.