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Genetic resistance elements carrying mef subclasses other than mef(A) in Streptococcus pyogenes.

ABSTRACT: In Streptococcus pyogenes, efflux-mediated erythromycin resistance is associated with the mef gene, represented mostly by mef(A), although a small portion of strains carry different mef subclasses. We characterized the composite genetic elements, including mef subclasses other than mef(A), associated with other resistance genes in S. pyogenes isolates. Determination of the genetic elements was performed by PCR mapping. The strains carrying mosaic mef(A/E), in which the 5' region was identical to mef(A) and the 3' region was identical to mef(E), also carried tet(O). The two genes were found enclosed in an element similar to S. pyogenes prophage ?m46.1, designated the ?m46.1-like element. In S. pyogenes strains carrying mef(E) and tet(M), mef(E) was included in a typical mega element, and in some strains, it was physically associated with tet(M) in the composite element Tn2009. S. pyogenes strains carrying mef(I) also carried catQ; the two genes were linked in a fragment representing a portion of the 5216IQ complex of Streptococcus pneumoniae, designated the defective IQ element. In the only isolate carrying a novel mef gene, this was associated with catQ and tet(M) in a genetic element similar to the 5216IQ complex of S. pneumoniae (5216IQ-like complex), suggesting that the novel mef is in fact a variant of mef(I). This study demonstrates that the composite elements containing mef are shared between S. pyogenes and S. pneumoniae and suggests that it is important to distinguish the mef subclass on the basis of the genetic element containing it.

SUBMITTER: Del Grosso M

PROVIDER: S-EPMC3122394 | biostudies-literature | 2011 Jul

REPOSITORIES: biostudies-literature

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Genetic resistance elements carrying mef subclasses other than mef(A) in Streptococcus pyogenes.

Del Grosso Maria M Camilli Romina R Barbabella Giada G Blackman Northwood John J Farrell David J DJ Pantosti Annalisa A

Antimicrobial agents and chemotherapy 20110418 7

In Streptococcus pyogenes, efflux-mediated erythromycin resistance is associated with the mef gene, represented mostly by mef(A), although a small portion of strains carry different mef subclasses. We characterized the composite genetic elements, including mef subclasses other than mef(A), associated with other resistance genes in S. pyogenes isolates. Determination of the genetic elements was performed by PCR mapping. The strains carrying mosaic mef(A/E), in which the 5' region was identical to ...[more]

PMID: 21502613

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Project description:This study was directed at characterizing the genetic elements carrying the methylase gene erm(B), encoding ribosome modification-mediated resistance to macrolide, lincosamide, and streptogramin B (MLS) antibiotics, in Streptococcus pyogenes. In this species, erm(B) is responsible for MLS resistance in constitutively resistant isolates (cMLS phenotype) and in a subset (iMLS-A) of inducibly resistant isolates. A total of 125 erm(B)-positive strains were investigated, 81 iMLS-A (uniformly tetracycline susceptible) and 44 cMLS (29 tetracycline resistant and 15 tetracycline susceptible). Whereas all tetracycline-resistant isolates carried the tet(M) gene, tet(M) sequences were also detected in most tetracycline-susceptible isolates (81/81 iMLS-A and 7/15 cMLS). In 2 of the 8 tet(M)-negative cMLS isolates, erm(B) was carried by a plasmid-located Tn917-like transposon. erm(B)- and tet(M)-positive isolates were tested by PCR for the presence of genes int (integrase), xis (excisase), and tndX (resolvase), associated with conjugative transposons of the Tn916 family. In mating experiments using representatives of different combinations of phenotypic and genotypic characteristics as donors, erm(B) and tet(M) were consistently cotransferred, suggesting their linkage in individual genetic elements. The linkage was confirmed by pulsed-field gel electrophoresis and hybridization studies, and different elements, variably associated with the different phenotypes/genotypes, were detected and characterized by amplification and sequencing experiments. A previously unreported genetic organization, observed in all iMLS-A and some cMLS isolates, featured an erm(B)-containing DNA insertion into the tet(M) gene of a defective Tn5397, a Tn916-related transposon. This new element was designated Tn1116. Genetic elements not previously described in S. pyogenes also included Tn6002, an unpublished transposon whose complete sequence is available in GenBank, and Tn3872, a composite element resulting from the insertion of the Tn917 transposon into Tn916 [associated with a tet(M) gene expressed in some cMLS isolates and silent in others]. The high frequency of association between a tetracycline-susceptible phenotype and tet(M) genes suggests that transposons of the Tn916 family, so far typically associated solely with a tetracycline-resistant phenotype, may be more widespread in S. pyogenes than currently believed.

Dataset Information

Genetic resistance elements carrying mef subclasses other than mef(A) in Streptococcus pyogenes.

Publications

Genetic resistance elements carrying mef subclasses other than mef(A) in Streptococcus pyogenes.

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