Abstract
Chromosome-borne antibiotic resistance, first described by us in 198111 in group A, B, and G streptococci, appears to be a common trait shared by different species of antibiotic- resistant streptococcal strains. A number of our previous investigations have demonstrated that in 90% of streptococci of group A, B, C, and G8 and 100% of Streptococcus bovis 7, Streptococcus pneumoniae 7, Streptococcus anginosus 3, Streptococcus mitis 1, and Streptococcus oralis 1 strains studied, antibiotic resistance determinants (chloramphenicol, macrolides and related drugs, tetracycline-minocycline, and high levels of aminoglycosides including streptomycin, kanamycin-neomycin, and gentamicin-kanamycin) are located on the chromosome. In most cases, chromosomal antibiotic resistance is mediated by mobile genetic elements10 such as Tn916-like structures6 or Tn3701-like composite structures12. More recently, we have identified two other categories of chromosomal elements, designated Tn916-modified1 which have sequences homologous to the conjugative transposon Tn916 6 but HincII stuctures different from that of Tn916: (i) in 14 (9.3%) of 151 streptococcal strains studied, the HincII profile varies from a strain to another but, apparently, these elements may transpose as Tn916 since they share DNA-DNA homology with the integrase gene and the two extremities of Tn916 5; (ii) four (7.0%) of 58 enterococcal strains studied possess similar if not identical HincII structures among themselves. The enterococcal Tn916-modified elements do not display DNA-DNA homology with the integrase gene or the extremities of Tn916. We suggest that the enterococcal Tn916-modified structures, unlike those detected in streptococci, belong to a new family of mobile genetic elements; the prototype of these elements is Tn3708 5.KeywordsMobile Genetic ElementStreptococcus AgalactiaeIntegrase GeneEnterococcal StrainChromosomal ElementThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
Published Version
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