erm(T)-Mediated Macrolide-Lincosamide Resistance in Streptococcus suis

Area of Science:

• Microbiology
• Antimicrobial Resistance
• Genetics

Background:

• Macrolide and lincosamide resistance in Gram-positive pathogens is a significant clinical challenge.
• The erm(T) gene is a primary determinant of resistance to these antibiotic classes.
• Streptococcus suis is an important zoonotic pathogen with increasing antimicrobial resistance concerns.

Purpose of the Study:

• To determine the presence and location of the erm(T) gene in clinical Streptococcus suis isolates.
• To investigate the transmissibility and fitness costs of erm(T)-carrying mobile genetic elements in S. suis.
• To understand the implications of erm(T) in S. suis for antimicrobial resistance and public health.

Main Methods:

• Broth microdilution for Minimum Inhibitory Concentrations (MICs).
• Polymerase Chain Reaction (PCR) for erm(T) detection.
• Whole-genome sequencing (WGS) for genetic environment analysis.
• Electrotransformation for assessing transmission.
• Competition experiments for fitness cost evaluation.

Main Results:

• The erm(T) gene was detected in 2 of 237 S. suis strains, located on a plasmid (pSC262) and an Integrative and Conjugative Element (ICE, ICESsuSC117).
• Both the plasmid and ICE were transmissible via transformation and conferred resistance in heterologous hosts like Staphylococcus aureus and Streptococcus pneumoniae.
• Carriage of the erm(T)-harboring plasmid or ICE resulted in a fitness cost for the S. suis host.

Conclusions:

• This is the first report of the erm(T) gene in S. suis, highlighting its presence on mobile genetic elements.
• The transmissibility of these elements poses a risk for the spread of macrolide-lincosamide resistance among Gram-positive bacteria.
• The observed fitness cost may contribute to the low prevalence of erm(T) in S. suis populations, but its potential for transmission remains significant.