virginiamycin and Chromosome-Deletion

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.

Topics: Anti-Bacterial Agents; Chromosome Deletion; Conjugation, Genetic; Drug Resistance, Microbial; Lincosamides; Macrolides; R Factors; Species Specificity; Streptococcus; Transduction, Genetic; Transformation, Bacterial; Virginiamycin

The inducibility of ermC by erythromycin, megalomicin, and celesticetin was tested with both wild-type ermC and several regulatory mutants altered in the 19-amino-acid-residue leader peptide, MGIFSIFVISTVHYQP NKK. In the model test system that was used, the ErmC methylase was translationally fused to beta-galactosidase. Mutational alterations that mapped in the interval encoding Phe-4 through Ile-9 of the leader peptide not only affected induction by individual antibiotics, but did so differentially. The subset of mutations that affected inducibility by the two macrolides erythromycin and megalomicin overlapped and were distinct from the subset of mutations that affected induction by celesticetin. These studies provide a model system for experimentally varying the relative efficiencies with which different antibiotics induce the expression of ermC. The possibility that antibiotics with inducing activity interact directly with the nascent leader peptide was tested by using a chemically synthesized decapeptide, MGIFSIFVIS--, attached at its C-terminus to a solid-phase support. This peptide, however, failed to bind erythromycin in vitro.

Topics: Amino Acid Sequence; Anti-Bacterial Agents; Bacillus subtilis; Base Sequence; beta-Galactosidase; Chromosome Deletion; Enzyme Induction; Kinetics; Lincosamides; Macrolides; Methyltransferases; Molecular Sequence Data; Mutation; Nucleic Acid Conformation; Protein Biosynthesis; Protein Sorting Signals; Recombinant Fusion Proteins; Virginiamycin

A naturally occurring constitutive macrolide-lincosamide-streptogramin B (MLS) resistance plasmid, pNE131, from Staphylococcus epidermidis was chosen to study the molecular basis of constitutive expression. Restriction and functional maps of pNE131 are presented along with the nucleotide sequence of ermM, the gene which mediates constitutive MLS resistance. Sharing 98% sequence homology within the 870-base-pair Sau3A-TaqI fragment, ermM appears to be almost identical to ermC, the inducible MLS resistance determinant from S. aureus (pE194). The two genes share nearly identical sequences, except in the 5' promoter region of ermM. Constitutive expression of ermM is due to the deletion of 107 base pairs relative to ermC; the deletion removes critical sequences for attenuation, resulting in constitutive methylase expression.

Topics: Amino Acid Sequence; Anti-Bacterial Agents; Base Sequence; Chromosome Deletion; DNA (Cytosine-5-)-Methyltransferases; Drug Resistance, Microbial; Gene Expression Regulation; Lincosamides; Macrolides; Nucleic Acid Conformation; Phenotype; Plasmids; Staphylococcus epidermidis; Virginiamycin