Assuntos
Resistência a Múltiplos Medicamentos/genética , Enterococcus faecium/efeitos dos fármacos , Enterococcus faecium/genética , Conjugação Genética , DNA Bacteriano/genética , DNA Bacteriano/isolamento & purificação , Enterococcus faecium/isolamento & purificação , Genes Bacterianos , Infecções por Bactérias Gram-Positivas/tratamento farmacológico , Infecções por Bactérias Gram-Positivas/microbiologia , Humanos , Testes de Sensibilidade Microbiana , Hibridização de Ácido Nucleico , Plasmídeos/genética , Plasmídeos/isolamento & purificaçãoRESUMO
An assay based on the utilization of degenerate primers that enable enzymatic amplification of an internal fragment of cat genes known to be present in gram-positive cocci was developed to identify the genes encoding chloramphenicol resistance in streptococci and enterococci. The functionality of this system was illustrated by the detection of cat genes belonging to four different hydridization classes represented by the staphylococcal genes catpC221, catpC194, catpSCS7, and the clostridial gene catP, and by the characterization of a new streptococcal cat gene designated catS. A sequence related to the clostridial catQ gene, which was present in one streptococcal strain, was not detected by this assay. These results reveal that these six cat genes account for chromosomal-borne chloramphenicol resistance in 12 group A, B, and G streptococci tested. By contrast, only three of these six cat genes (catpC221, catpC194, and catpSCS7) were detected on the 10 enterococcal plasmids studied here that encode resistance to chloramphenicol.
Assuntos
Cloranfenicol O-Acetiltransferase/genética , Enterococcus faecium/enzimologia , Enterococcus faecium/genética , Genes Bacterianos/genética , Reação em Cadeia da Polimerase/métodos , Streptococcus/enzimologia , Streptococcus/genética , Sequência de Aminoácidos , Sequência de Bases , Primers do DNA/genética , Amplificação de Genes/genética , Variação Genética , Dados de Sequência Molecular , Plasmídeos/genética , Streptococcus agalactiae/enzimologia , Streptococcus agalactiae/genéticaRESUMO
Seventeen oral streptococci and 18 enterococci were tested for the presence of DNA sequences homologous to the conjugative transposon Tn916 encoding tetracycline resistance. All the strains were resistant to tetracyclines, including minocycline, and most of them were resistant to other antibiotics. Tn916-like structures, identified by hybridization of HincII-digested DNA, were found on the chromosomes of 11 oral streptococci and four enterococci and on two plasmids, pIP1549 and pIP1440, one harbored by an Enterococcus hirae strain and the other harbored by an Enterococcus faecalis strain. Sequences homologous to Tn916, only some of which corresponded to its internal HincII structure (Tn916-modified elements), were chromosomally located in three oral streptococci and two enterococci and were plasmid borne in pIP614 harbored by an E. faecalis strain. Nine enterococci and three oral streptococci carried either the Tet M or the Tet O determinant chromosomally, but they carried no other sequences homologous to Tn916.
Assuntos
DNA Bacteriano/genética , Enterococcus/genética , Streptococcus/genética , Antibacterianos/farmacologia , Elementos de DNA Transponíveis/efeitos dos fármacos , DNA Bacteriano/efeitos dos fármacos , Resistência Microbiana a Medicamentos , Enterococcus/efeitos dos fármacos , Hibridização Genética , Plasmídeos , Streptococcus/efeitos dos fármacosRESUMO
The tetracycline (Tet) determinants, which encode resistance either to tetracyclines without minocycline (Tcr) or to tetracyclines including minocycline (Tcr-Mnr), of 30 wild-type clinical isolates of Enterococcus faecium were identified and localized. The Tet determinants were transferred by conjugation into a plasmid-free Enterococcus faecalis recipient at frequencies of 10(-6) to 10(-9) transconjugants per donor, as follows: Tcr, 6 strains; Tcr-Mnr, 14 strains; both Tcr and Tcr-Mnr, 6 strains; no detectable transfer, 4 strains. Classes L (Tcr phenotype) and M and O (Tcr-Mnr phenotype) of the Tet determinants were identified by DNA-DNA hybridization experiments. The Tet L determinant was plasmid-borne in 18 strains and was chromosomal in 2 strains. Tet M was chromosomal in 27 strains and plasmid-borne (pIP1534) in 1 strain; pIP1534 also carried Tet L. Tet M was located on Tn916-like elements in 22 strains and on a Tn916-modified element in 1 strain. Tet O was detected in only one strain in which it was plasmid-borne. Both Tet L and Tet M determinants were carried by 19 strains. One strain carried, in addition to chromosomal nonconjugative Tet L and Tet M determinants, a conjugative Tcr-Mnr marker which did not correspond to any Tet determinant tested in this study. These results attest to the genetic complexity of tetracycline resistance in E. faecium strains.
