erm(T)-Mediated Macrolide-Lincosamide Resistance in Streptococcus suis
Rui Yu1, Yindi Xu2, Stefan Schwarz3
1College of Veterinary Medicine, Henan Agricultural Universitygrid.108266.b, Zhengzhou, People's Republic of China.
Abstract:
To investigate the presence and location of erm(T) in clinical Streptococcus suis isolates and explore the transmission ability and fitness cost of erm(T)-carrying mobile genetic elements among S. suis isolates, MICs were determined by broth microdilution. The presence of erm(T) in S. suis was detected by PCR. The genetic environment of erm(T) in S. suis was explored by whole-genome sequencing (WGS) analysis. Intraspecies and interspecies transmission were examined by electrotransformation. The fitness cost associated with the carriage of an erm(T)-harboring plasmid or an integrative and conjugative element (ICE) was examined by competition experiments. Of 237 nonduplicate strains, erm(T) was detected in 2 S. suis strains (SC262-ST954 and SC117-ST1314), with its location on a 5,125-bp plasmid in S. suis SC262 and on a 64,013-bp ICESsuSC117 in S. suis SC117, respectively. Both the erm(T)-carrying plasmid pSC262 and the ICESsuSC117 were transmissible by transformation. Plasmid pSC262 can replicate and express macrolide-lincosamide resistance in heterologous hosts, including S. aureus and S. pneumoniae. Both the erm(T)-carrying plasmid and the ICE posed a fitness cost to the host S. suis isolate. To the best of our knowledge, this is the first report of the macrolide-lincosamide-streptogramin B resistance gene erm(T) in S. suis. Its location on a plasmid or an ICE will aid in its transmission. The low detection rate of erm(T) gene among the S. suis population might be due to the fitness cost of the erm(T)-carrying plasmid and ICE. IMPORTANCE Macrolide and lincosamide resistance due to the presence of erm(T) have posed a challenge for the treatment of Gram-positive pathogens. Although the low detection rate of erm(T) gene among the S. suis population due to the fitness cost of the erm(T)-carrying plasmid and ICE, the presence of erm(T) in S. suis and its potential transmission to other Gram-positive pathogens will be of important significance.
Insights
The macrolide resistance gene erm(T) was found in Streptococcus suis, located on mobile genetic elements like plasmids and ICEs. These elements are transmissible but impose a fitness cost on the bacteria, potentially explaining their low prevalence.
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.
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