Biomedical subjects

T Horaud

Publications and source records attributed to T Horaud.

At least 37 records · Page 2Linked to original sources

PubMed1992

Natural occurrence of structures in oral streptococci and enterococci with DNA homology to Tn916.

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.

Anti-Bacterial Agents↗

PubMed1992

Identical genes confer high-level resistance to gentamicin upon Enterococcus faecalis, Enterococcus faecium, and Streptococcus agalactiae.

The structural gene coding for the bifunctional aminoglycoside-modifying 6'-acetyltransferase-2''-phosphotransferase (6'AAC-2''APH) enzyme was specifically amplified by the polymerase chain reaction using template DNA of clinical isolates of enterococci (both Enterococcus faecalis and Enterococcus faecium) and the single high-level gentamicin-resistant Streptococcus agalactiae strain identified thus far. The results of the present study demonstrated that the genes encoding this antibiotic resistance trait are highly homologous in these species. In dot blot hybridization assays using nonradioactively labeled oligonucleotide probes, strains with and without high-level gentamicin resistance could be discerned unequivocally. The gene segment encoding 6'-acetylating activity and the gene segment encoding 2''-phosphorylating activity were simultaneously present in all isolates exhibiting high-level gentamicin resistance.

Acetyltransferases↗

PubMed1991

Tetracycline resistance heterogeneity in Enterococcus faecium.

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.

Chromosomes, Bacterial↗

PubMed1990

Tn3702, a conjugative transposon in Enterococcus faecalis.

Enterococcus faecalis strain D434 was found to carry on its chromosome a determinant encoding tetracycline-minocycline resistance (Tcr-Mnr) and to harbor both an R plasmid and a cryptic conjugative plasmid, pIP1141. The determinant coding for Tcr-Mnr was located on a conjugative transposon, designated Tn3702. The transposition of Tn3702 on to both pIP1141 and the hemolysin plasmid pIP964 yielded different derivatives each of which contained an 18.5-kilobase insert. The structure of Tn3702 is similar to that of the conjugative transposon Tn916.

Conjugation, Genetic↗

PubMed1990

High-level chromosomal gentamicin resistance in Streptococcus agalactiae (group B).

This is the first report of high-level gentamicin resistance in a group B streptococcus. Strain B128 of serotype II was isolated from an infected leg wound in 1987. B128 was resistant to high levels of gentamicin as well as of all other available aminoglycosides and was also resistant to tetracyclines. No bactericidal synergism was found between ampicillin or vancomycin and any of these aminoglycosides. Gentamicin, kanamycin, streptomycin, and tetracycline resistance determinants transferred by conjugation into a plasmid-free group B streptococcus recipient at a frequency of 10(-8) to 10(-9) transconjugants per donor cell. No transconjugants were detected when streptococci of groups A, C, and G, Streptococcus sanguis, or Enterococcus faecalis was used as a recipient. No plasmids were detected in B128 or in any of the four transconjugants tested. By DNA-DNA hybridization, homology was detected between gene aac6/aph2, of E. faecalis origin, and a 2.4-kilobase HindIII chromosomal fragment of B128; homology to the genes aph3 and aadE, of E. faecalis origin, was found with HindIII chromosomal fragments of the same size (3.0 kilobases). Strains like B128, which potentially can be responsible for severe neonatal infections, are of great clinical concern, since there are to date no antibiotic combinations exhibiting bactericidal synergism against them.

Blotting, Southern↗

PubMed1990

Does a tetracycline resistance determinant of class N exist?

pMV120 was reported to carry the tetracycline resistance (Tcr) determinant of class N. We obtained tetracycline-susceptible transconjugants harboring plasmids with restriction enzyme profiles indistinguishable from those of pMV120 isolated from tetracycline-resistant clones. We conclude that pMV120 is a cryptic plasmid and that class N of Tcr determinants does not exist.

Cloning, Molecular↗

PubMed1990

Identification of chromosomal antibiotic resistance genes in Streptococcus anginosus ("S. milleri").

Determinants encoding resistance to antibiotics, except penicillin, of 5 of 21 Streptococcus anginosus clinical isolates that we examined transferred by conjugation into Enterococcus faecalis and into 1 to 5 streptococcal recipients at frequencies of 10(-6) to 10(-8) transconjugants per donor. No R plasmids were detected in any wild-type strain. DNA homology was detected between chromosomal fragments and the following genes: aadE in 7 strains that were highly resistant to streptomycin, aph-3 in 8 strains that were highly resistant to kanamycin, ermB in 11 of 15 strains that were resistant to erythromycin, and tetM in 14 and tetO in 3 of the 18 strains that were resistant to tetracycline-minocycline. A Tn916-like structure was found in 10 of the 14 strains that carried the tetM gene.

Chromosomes↗

PubMed1990

Presence of chromosomal elements resembling the composite structure Tn3701 in streptococci.

Tn3701, carried by Streptococcus pyogenes A454, is the first chromosomal composite element to be described; it contains in its central region Tn3703, a transposon similar to Tn916. A comparison by DNA-DNA hybridization of Tn3701 with omega(cat-tet) and Tn3951, carried by Streptococcus pneumoniae BM6001 and by Streptococcus agalactiae B109, respectively, revealed that the two latter structures are also Tn3701-like composite elements. The DNAs of 27 other antibiotic-resistant group A, B, C, and G streptococci and of S. pneumoniae BM4200 showed sequence homologies to Tn3701 (14 strains, including BM4200), to the regions of Tn3701 outside of Tn3703 (5 strains), and to Tn916 alone (8 strains). The DNAs of five strains did not detectably hybridize with any probe. The tetM gene was identified in most chromosomal genetic elements coding for tetracycline-minocycline resistance. Since Tn3701-like elements are widely disseminated among antibiotic-resistant streptococci (47% of the 34 strains studied), we propose that Tn3701 be considered the prototype of chromosomal composite elements.

Chromosome Mapping↗

PubMed1989

Genetic basis of antibiotic resistance in Aerococcus viridans.

Resistance to at least one of the following antibiotics was found in eight wild-type strains of Aerococcus viridans: erythromycin (six strains), tetracycline and minocycline (five strains), chloramphenicol (one strain), and high levels of streptomycin (one strain). None of the strains transferred any of their antibiotic resistance markers into streptococcal, enterococcal, or A. viridans recipients by conjugation. By DNA-DNA hybridization experiments, the ermB gene of transposon Tn917, of Enterococcus faecalis origin, was detected in five of the six strains resistant to erythromycin and was localized for one strain on the chromosome and for four strains on nonconjugative small (4.7- to 4.9-kilobase) plasmids. The tetM gene of the conjugative transposon Tn916, of E. faecalis origin, was localized on the chromosome of four of the five strains resistant to tetracycline and minocycline; in three of these strains a structure similar to that of Tn916 was found. Homology to the tetO gene of pUA466, of Campylobacter jejuni origin, was detected on the chromosome of the fifth strain. No sequence homology was detected in any strain with probes corresponding to the tetL gene of group B Streptococcus origin, to the ermA gene of the transposon Tn554 of Staphylococcus aureus origin, or to the cat genes of either pC194 or pC221 of S. aureus origin.

Anti-Bacterial Agents↗

PubMed1988

Heterogeneity of chromosomal genes encoding chloramphenicol resistance in streptococci.

The DNA of 21 chloramphenicol-resistant plasmid-free streptococci was tested for sequence homology with the genes encoding chloramphenicol acetyltransferase (cat) of the staphylococcal plasmids pC194 and pC221. Homology to the cat gene of pC194 was detected in 11 strains, including the 8 strains of Streptococcus pneumoniae examined, and homology to cat of pC221 was found in 3 strains. The DNA of 7 strains did not detectably hybridize with either probe.

Acetyltransferases↗

PubMed1988

Molecular analysis of a composite chromosomal conjugative element (Tn3701) of Streptococcus pyogenes.

The plasmid-free Streptococcus pyogenes A454 contains a conjugative element, Tn3701, encoding resistance to erythromycin (Emr), tetracycline (Tcr), and minocycline (Mnr). We have mapped a 50-kilobase (kb) chromosomal region of A454 corresponding to the internal part of Tn3701. Tn3701 includes a 19.7-kb structure, designated Tn3703, on which the Emr Tcr Mnr determinants were localized. Tn3703 was very similar in structure to Tn916. Translocation of the Emr Tcr Mnr markers from A454 onto pIP964, an Enterococcus faecalis hemolysin plasmid, yielded different pIP964 derivatives. When the inserts of four of these derivatives were aligned with the 50-kb region of Tn3701, three of them were found to result from the transposition of Tn3703 and one resulted from the insertion of a 44.0-kb portion of Tn3701, including Tn3703. Tn3701 inserted, apparently without changing its structure, in the chromosomes of various streptococcal transconjugants, as well as in one of the 12 E. faecalis transconjugants studied. Tn3703 inserted at different chromosomal sites in four E. faecalis transconjugants, and one copy of Tn3701 plus an additional copy of Tn3703 were detected in the chromosomes of seven transconjugants.

Cloning, Molecular↗

PubMed1987

Location of antibiotic resistance markers in clinical isolates of Enterococcus faecalis with similar antibiotypes.

Eight wild-type strains of Enterococcus faecalis, resistant to chloramphenicol (Cmr), erythromycin (Emr), tetracycline (Tcr), and minocycline (Mnr), were examined for the genetic basis of their antibiotic resistance, Five of the strains transferred all of their antibiotic resistance markers by conjugation, while the other three strains transferred only Tcr and Mnr. Cmr and Emr determinants were localized by DNA-DNA hybridization experiments, in which the Cmr gene of plasmid pIP501, of group B Streptococcus origin, and the Emr gene of transposon Tn917, of E. faecalis origin, served as probes. A chromosomal location was found for the nonconjugative Cmr and Emr markers of one wild-type strain. In two strains these markers were carried by nonconjugative plasmids, and in the other strains they were carried by plasmids that transferred by conjugation. Plasmids isolated from three transconjugants resistant to tetracycline but susceptible to minocycline bore nucleotide sequences homologous to the tetL gene. Nucleotide sequences homologous to conjugative transposon Tn916, of E. faecalis origin, were detected by hybridization in the tetracycline-minocycline-resistant transconjugants. Three of these transconjugants were plasmid free, while four harbored conjugative cryptic plasmids. Sequences homologous to Tn916 were also found on two conjugative plasmids, one of which appeared to be a conjugative cryptic plasmid that had acquired chromosomal Tcr Mnr markers during transfer.

Chloramphenicol Resistance↗

PubMed1987

Enterococcus faecalis hemolysin-bacteriocin plasmids belong to the same incompatibility group.

Plasmid pair coexistence was studied both among nine Enterococcus faecalis hemolysin-bacteriocin (Hly-Bcn) plasmids, including pJH2, pAD1, pAM gamma 1, and pIP964, and between pIP964 and five R plasmids. Some of the Hly-Bcn plasmids used were derivatives encoding resistance to erythromycin or tetracycline. The Hly-Bcn plasmids were incompatible with each other; 40 to 100% displacement was observed bilaterally for eight pairs and unilaterally for one pair. In contrast, pIP964 stably coexisted with each of the R plasmids. Entry exclusion was associated with incompatibility for most of the Hly-Bcn plasmids. The nine Hly-Bcn plasmids harbored by E. faecalis form a distinct incompatibility (Inc) group, designated IncHly.

Bacteriocins↗

PubMed1986

Dispersal of a plasmid-borne chloramphenicol resistance gene in streptococcal and enterococcal plasmids.

Plasmids coding for chloramphenicol resistance, five isolated from streptococci of groups A, B, and G, ten from enterococci (Enterococcus faecalis, Enterococcus faecium), and two from staphylococci, were tested for sequence homology with the chloramphenicol resistance gene of pIP501, a 30-kb plasmid originally isolated from a group B Streptococcus. The 6.3-kb HindIII fragment of pIP501, known to carry the chloramphenicol resistance gene, was cloned into pBR322. A 1.6-kb portion of the cloned fragment, which included most of the chloramphenicol resistance gene, was used as probe in DNA-DNA hybridization experiments. Sequence homology was detected between the probe and four of the streptococcal, seven of the enterococcal, and one of the staphylococcal plasmids. The absence of hybridization between this probe and one plasmid isolated from a group B Streptococcus, as well as three isolated from E. faecalis, indicated that there are at least two different plasmid-borne chloramphenicol resistance determinants in the streptococci and in the enterococci.

Chloramphenicol↗

PubMed1986

Use of penicillin-binding proteins for the identification of enterococci.

The results of 20 physiological and fermentation tests and examination of the penicillin-binding proteins (PBPs) of 85 enterococcal strains demonstrated that the genus Enterococcus could be divided into at least nine distinct species: E. faecalis, E. faecium, E. durans, E. hirae, E. avium, E. gallinarum, E. casseliflavus, E. malodoratus and E. mundtii. Each species had a specific pattern of at least five PBPs, with molecular masses in the range of about 40-130 kDa. The pattern of PBPs may be useful for identification purposes, since some strains with unusual fermentation characteristics were assigned to species by this technique.

Bacterial Proteins↗

PubMed1985

Molecular genetics of resistance to macrolides, lincosamides and streptogramin B (MLS) in streptococci.

Resistance to macrolides-lincosamides-streptogramin B (MLS phenotype) appears in almost all streptococcal species isolated from man. Genes coding for MLS resistance are located on plasmids and one MLS resistance transposon has been described. MLS resistance genes have also been found in a large number of plasmid-free strains. Plasmids of 17 to 20 megadaltons (Mdal) that code either for MLS or for both MLS and chloramphenicol resistance are found in streptococci of groups A, B, C, D (Streptococcus faecalis) and G. These plasmids have broad host ranges (conjugative intraspecies, interspecies and intergeneric transfer), display similar restriction enzyme patterns and share a considerable degree of homology (78 to 95%). One smaller non-conjugative MLS resistance plasmid has been isolated from Str. sanguis (4.5 Mdal). In group D (Str. faecalis, Str. faecium) streptococci, MLS resistance genes are also found on plasmids that carry other antibiotic resistance (tetracycline, chloramphenicol, high-levels of streptomycin and kanamycin). These multi-resistance plasmids are either conjugative or non-conjugative and are of various sizes and molecular species and those that have been tested have narrow host-ranges. The MLS resistance genes of one multi-resistant plasmid, isolated from a strain of Str. faecalis, are located on a transposon of 3.3 Mdal, Tn917. Hybridization studies, with MLS determinants as probes, reveal homologies among various plasmid-borne MLS resistance sequences. Elements that are thought to be chromosome-borne mediate multiple antibiotic resistance (including MLS) in streptococci of groups A, B, C, D (Str. bovis), F, G, Str. pneumoniae, Str. mitis, Str. sanguis and Str. milleri. Strains harbouring such elements contain no detectable plasmid DNA. In some of the strains these elements are conjugative; their resistance markers transfer en bloc at low frequency and display narrow host ranges. Such elements, from Str. pyogenes and Str. agalactiae, were found to translocate onto various streptococcal haemolysin-bacteriocin plasmids.

Anti-Bacterial Agents↗

PubMed1985

One or two low affinity penicillin-binding proteins may be responsible for the range of susceptibility of Enterococcus faecium to benzylpenicillin.

Three benzylpenicillin-resistant, clinical isolates of Enterococcus faecium (MIC values 16-64 micrograms ml-1) contained six penicillin-binding proteins (PBPs), of which PBP5 was the most abundant and had the lowest affinity for the antibiotic. Four benzylpenicillin-susceptible strains (MIC values 0.031-0.5 microgram ml-1) were obtained as spontaneous derivatives from these above organisms. There were significant decreases in the amounts of PBP5 in each of the derivatives, with the concomitant appearance of a new, higher affinity PBP (5*) in three strains. Increased amounts of PBP5, with no changes in PBP5*, were found in several mutants with intermediate-level benzylpenicillin-resistance (MIC values 1-8 micrograms ml-1) selected from two of the susceptible strains. Examination of 18 other clinical isolates, with a wide range of susceptibilities to benzylpenicillin (MIC values 0.062-128 micrograms ml-1), showed that PBP5* was present in 13 strains, and PBP5 in all of them, but in differing amounts. The results concerning the relative amounts and relative affinities of PBPs 5* and 5 allowed the categorization of the various strains into six groups, within which organisms had somewhat similar susceptibilities to benzylpenicillin.

Bacterial Proteins↗

PubMed1984

Translocation of antibiotic resistance markers of a plasmid-free Streptococcus pyogenes (group A) strain into different streptococcal hemolysin plasmids.

Wild-type strain A454 (Streptococcus pyogenes) transferred en bloc its erythromycin (Em) and tetracycline (Tc) resistance markers into several plasmid-free streptococcal recipients. No plasmid DNA was detected in either the wild-type or the transconjugant strains. Crosses were performed between A454 and S. faecalis Rec+ or Rec- recipients carrying hemolysin-bacteriocin plasmids, pIP964 or pAD1 . The Em Tc-resistant transconjugants obtained harbored either the parental plasmid or an Em Tc resistance plasmid derived from pIP964 or pAD1 . The restriction endonuclease analysis of 12 derivative plasmids showed insertions of various sizes into different fragments of pIP964 or pAD1 . A454 and the Em Tc-resistant plasmid-free transconjugants were found to contain two EcoRI DNA fragments, that shared homology with 32P-labeled pIP1077 , one of the Em Tc resistance derivative plasmids, but not with 32P-labeled pIP964 . No homology was detected between pIP1077 and the cellular DNA of the antibiotic-susceptible recipients.

Conjugation, Genetic↗