MLS antibiotics that bind to the 50S ribosomal subunit and inhibit protein synthesis include tylosin, tilmicosin, erythromycin, clindamycin, and lincomycin. Strepto-gramins are also part of the multiantibiotic formulation Synercid. The most common resistance to macrolides and lincosamides is by posttranscriptional covalent modification of the 23S ribosomal RNA by adenine-N6-methyl-transferase. Efflux pump systems for exporting MLS antibiotics out of the cell have become increasingly encountered, and these vary in their specificity, exporting either specific MLS antibiotics only or groups of MLS antibiotics. Moreover, resistance can be conferred by inactivation of specific MLS antibiotics by hydrolysis or removal of functional groups. Covalent modification of lincosamides has also been detected.
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