Abstract
Macrolide antibiotics (Mac) consist of a 12- to 16-membered lactone ring combined with a sugar moiety, and they inhibit protein synthesis via binding to 23S ribosomal RNA in bacteria. The 14- and 16-membered Mac are used for treating infectious diseases caused by Gram-positive and other bacteria; e.g., Haemophilus influenzae, Bordetella pertussis, Legionella pneumophila, Campylobacter, Treponema pallidum and Mycoplasma. Resistance to macrolide, lincosamide, and streptogramin-B (MLS) antibiotics in staphylococci is known to have the following mechanisms: 1) alteration of the target on ribosome due to dimethylation of a specific adenine residue in the 23S ribosomal RNA by the product of the erm gene, and consequently a decrease in binding of MLS antibiotics; 2) inactivation of streptogramin-B (STG-B) and lincosamide by the products of the sbh (encoding streptogramin B hydrolase) and linA' (encoding 3-lincomycin 4-clindamycin O-nucleotidyltransferase) genes, respectively; and 3) active efflux of Mac and STG-B antibiotics determined by the msrA and msrB genes in Staphylococcus epidermidis and Staphylococcus xylosus, respectively, both of which appear to act as an ATP-dependent efflux pump. I have shown that Staphylococcus aureus 8325(pEP2104) exhibits inducible resistance to PMS (partial macrolide and streptogramin B)-antibiotics [the 14-membered macrolides, erythromycin (EM), and oleandomycin (OL), and the 16-membered macrolide mycinamicin (MCM) and STG-B]. The sequence of the N-terminal amino acid residues of a 63 kDa protein (MsrSA) that appeared in the membrane of PMS-resistant strains was identical to that of an MsrA polypeptide related to enhanced efflux of [14C]EM. Ribosomes from PMS-resistant strains showed a similar affinity for EM to those from the PMS-sensitive host strain NCTC8325, and no inactivation of EM by 8325(pEP2104) was observed. In the present study, I showed the DNA sequence of the msrSA region on the constitutive PMS-resistant plasmid pMC38, PMS-inducible resistant plasmid pEP2104 and PMS-sensitive mutant plasmid pSP6, and the region that is essential for inducible expression in PMS resistance. In addition, I investigated the relationship between PMS resistance and intracellular accumulation of EM.
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