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The novel conjugative transposon tn1207.3 carries the macrolide efflux gene mef(A) in Streptococcus pyogenes
Maria Santagati1, Francesco Iannelli, Carmela Cascone
1Department of Microbiology, University of Catania, 95124 Catania, Italy. santagatim@tiscali.it
Abstract:
The macrolide efflux gene mef(A) of the Streptococcus pyogenes clinical strain 2812A was found to be carried by a 52-kb chromosomal genetic element that could be transferred by conjugation to the chromosome of other streptococcal species. The characteristics of this genetic element are typical of conjugative transposons and was named Tn1207.3. The size of Tn1207.3 was established by pulsed-field gel electrophoresis (PFGE), and DNA sequencing analysis showed that the 7,244 bp at the left end of Tn1207.3 were identical to those of the pneumococcal Tn1207.1 element. Tn1207.3-like genetic elements were found to be inserted at a single specific chromosomal site in 12 different clinical isolates S. pyogenes exhibiting the M phenotype of resistance to macrolides and carrying the mef(A) gene. Tn1207.3 was transferred from S. pyogenes 2812A to Streptococcus pneumoniae, and sequence analysis carried out on six independent transconjugants showed that insertion of Tn1207.3 in the pneumococcal genome always occurred at a single specific site as in Tn1207.1. Using MF2, a representative S. pneumoniae transconjugant, as a donor, Tn1207.3 was transferred again by conjugation to S. pyogenes and Streptococcus gordonii. The previously described nonconjugative element Tn1207.1 of S. pneumoniae appears to be a defective element, part of a longer conjugative transposon that carries mef(A) and is found in clinical isolates of S. pyogenes.
Insights
A mobile genetic element, Tn1207.3, carrying the macrolide efflux gene mef(A) was identified in Streptococcus pyogenes. This conjugative transposon can transfer the mef(A) gene between streptococcal species, contributing to macrolide resistance.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Macrolide resistance is a growing concern in bacterial infections.
- The mef(A) gene confers resistance to macrolide antibiotics.
- Mobile genetic elements play a crucial role in the dissemination of antibiotic resistance genes.
Purpose of the Study:
- To characterize the genetic element carrying the mef(A) gene in Streptococcus pyogenes.
- To investigate the transferability and insertion characteristics of this element in other streptococcal species.
Main Methods:
- Pulsed-field gel electrophoresis (PFGE) to determine element size.
- DNA sequencing to analyze genetic element structure and homology.
- Conjugation experiments to assess transferability between bacterial species.
Main Results:
- A 52-kb conjugative transposon, named Tn1207.3, carrying the mef(A) gene was identified in S. pyogenes.
- Tn1207.3 shares homology with the pneumococcal Tn1207.1 element.
- Tn1207.3 was successfully transferred to Streptococcus pneumoniae and Streptococcus gordonii, inserting at a specific chromosomal site.
- Tn1207.1 appears to be a defective part of a larger conjugative element.
Conclusions:
- Tn1207.3 is a mobile genetic element responsible for the spread of the mef(A) gene in S. pyogenes.
- The conjugative nature of Tn1207.3 facilitates the horizontal transfer of macrolide resistance among streptococci.
- Understanding the mobility of such elements is critical for combating antibiotic resistance.