Abstract
Multiple resistance of Streptococcus pneumoniae is generally associated with their unique recombination-mediated genetic plasticity and possessing the mobile genetic elements. The aim of our study was to detect antibiotic resistance determinants and conjugative transposons in 138 antibiotic-resistant pneumococcal strains isolated from nasopharynx of healthy young children from Lublin, Poland. These strains resistant to tetracycline and/or to chloramphenicol/erythromycin/clindamycin were tested by PCR using the specific genes as markers. The presence of Tn916 family transposons, carrying tet(M) and int/xisTn916, was observed in all of the tested strains. Tn916 was detected in 16 strains resistant only to tetracycline. Tn6002 and Tn3872-related element were found among 99 erm(B)-carrying strains (83.8% and 3.0%, resp.). Eight strains harbouring mef(E) and erm(B) genes were detected, suggesting the presence of Tn2010 and Tn2017 transposons. Among 101 chloramphenicol-resistant strains, two variants of Tn5252-related transposon were distinguished depending on the presence of int/xis5252 genes specific for cat gene-containing Tn5252 (75.2% of strains) or int Sp23FST81 gene, specific for cat-containing ICESp23FST81 element (24.8% of strains). In 6 strains Tn916-like and Tn5252-like elements formed a Tn5253-like structure. Besides clonal dissemination of resistant strains of pneumococci in the population, horizontal transfer of conjugative transposons is an important factor of the high prevalence of antibiotic resistance.
Highlights
Antimicrobial resistance among Streptococcus pneumoniae has spread worldwide and it causes higher risk of treatment failure in pneumococcal infections
On the basis of the erythromycin-clindamycin-rokitamycin triple-disk test, 82 of the 99 strains resistant to erythromycin and clindamycin were assigned to the cMLS phenotype, 17 were assigned to the iMcLS phenotype, and none was assigned to the iMLS phenotype or to the M phenotype
Antibiotic resistance in S. pneumoniae is often carried by the mobile genetic elements that reside in the chromosome, such as conjugative transposons
Summary
Antimicrobial resistance among Streptococcus pneumoniae has spread worldwide and it causes higher risk of treatment failure in pneumococcal infections. Nasopharyngeal carriage in healthy children is a major factor in the horizontal transmission of pneumococcal strains, especially between children attending day care centers (DCCs) or to other family members, and may be the source of infection in other individuals. Multiple resistance of pneumococci especially resistance to macrolides and tetracyclines as well as to chloramphenicol is generally associated with their unique recombinationmediated genetic plasticity and possessing the mobile genetic elements [3, 4]. The majority of macrolide-resistant S. pneumoniae strains are resistant to tetracycline. This association is due to the insertion of erm(B) into conjugative and composite transposons of the Tn916 family that harbours tet(M) gene, encoding ribosome protection proteins.
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