Composite mobile genetic elements disseminating macrolide resistance in Streptococcus pneumoniae

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• Macrolide resistance in Streptococcus pneumoniae emerged globally in the early 1990s.
• Key resistance factors include erm(B) and macrolide efflux genes mef(E)/mel.
• These genes are found on mobile genetic elements within pneumococci.

Purpose of the Study:

• To investigate the diversity and evolution of mobile elements conferring macrolide resistance.
• To analyze these elements in pneumococcal isolates from pre- and post-conjugate vaccine eras.
• To characterize novel insertion sites and understand dissemination mechanisms.

Main Methods:

• Genomic analysis of 131 Streptococcus pneumoniae isolates (121 invasive, 10 carriage) from Atlanta (1994-2011).
• Focus on 100 macrolide-resistant invasive isolates to identify mobile elements.
• Characterization of insertion sites for Mega, erm(B) element, Tn917, and Tn916-like elements.

Main Results:

• Tn916-like elements with mef(E)/mel (on Mega) and erm(B) (on erm(B) element/Tn917) were identified.
• Elements integrated into the pneumococcal chromosome and larger Tn5253-like composite elements.
• Novel insertion sites for Mega were found, and Tn916-like element insertion sites were characterized.

Conclusions:

• Conjugative mobile elements facilitate acquisition of DNA from diverse bacteria.
• Recombination is the predominant mechanism for transmitting novel DNA within pneumococcal populations post-integration.
• Understanding these mechanisms is crucial for tracking antibiotic resistance evolution.