Retapamulin Inhibition of Translation and 50S Ribosomal Subunit Formation in Staphylococcus aureus Cells

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The continuing increase in antibiotic-resistant microorganisms is driving the search for new antibiotic targets and improved antimicrobial agents. Ketolides are semisynthetic derivatives of macrolide antibiotics, which are effective against certain resistant organisms. Solithromycin (CEM-101) is a novel fluoroketolide with improved antimicrobial effectiveness. This compound binds to the large 50S subunit of the ribosome and inhibits protein biosynthesis. Like other ketolides, it should impair bacterial ribosomal subunit formation. This mechanism of action was examined in strains of Streptococcus pneumoniae, Staphylococcus aureus, and Haemophilus influenzae. The mean 50% inhibitory concentrations (IC 50 s) for solithromycin inhibition of cell viability, protein synthesis, and growth rate were 7.5, 40, and 125 ng/ml for Streptococcus pneumoniae, Staphylococcus aureus, and Haemophilus influenzae, respectively. The net formation of the 50S subunit was reduced in all three organisms, with IC 50 s similar to those given above. The rates of 50S subunit formation measured by a pulse-chase labeling procedure were reduced by 75% in cells growing at the IC 50 of solithromycin. Turnover of 23S rRNA was stimulated by solithromycin as well. Solithromycin was found to be a particularly effective antimicrobial agent, with IC 50 s comparable to those of telithromycin and significantly better than those of azithromycin and clarithromycin in these three microorganisms.

Section: Discussionsupporting

confidence: 67%

“…with the control MSSA organism (27). The compound was also effective in treating S. aureus-infected macrophage cells (28).…”

Section: Discussionmentioning

confidence: 86%

Solithromycin Inhibition of Protein Synthesis and Ribosome Biogenesis in Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae

Rodgers

Frazier

Champney

2013

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“…The drugs proposed to have such an effect included macrolides and ketolides (10,11,15,35,59), streptogramin B (16), lincosamides (16), aminoglycosides (36), evernimicin (14), linezolid (12), and pleuromutilins (13). However, the indirect mechanism of assembly inhibition cannot be excluded for any of these drugs.…”

mentioning

confidence: 99%

Erythromycin- and Chloramphenicol-Induced Ribosomal Assembly Defects Are Secondary Effects of Protein Synthesis Inhibition

Siibak

Peil

Xiong

et al. 2009

Several protein synthesis inhibitors are known to inhibit ribosome assembly. This may be a consequence of direct binding of the antibiotic to ribosome precursor particles, or it could result indirectly from loss of coordination in the production of ribosomal components due to the inhibition of protein synthesis. Here we demonstrate that erythromycin and chloramphenicol, inhibitors of the large ribosomal subunit, affect the assembly of both the large and small subunits. Expression of a small erythromycin resistance peptide acting in cis on mature ribosomes relieves the erythromycin-mediated assembly defect for both subunits. Erythromycin treatment of bacteria expressing a mixture of erythromycin-sensitive and -resistant ribosomes produced comparable effects on subunit assembly. These results argue in favor of the view that erythromycin and chloramphenicol affect the assembly of the large ribosomal subunit indirectly.The ribosome is a target for many medically important antibiotics (42,56,63). These drugs bind to either the small or the large subunit and inhibit essential ribosome functions: decoding, peptidyl transfer, transit of the nascent peptide chain, or activation of ribosome-associated GTPases. In addition, antibiotics cause many physiological changes; for example, they induce stress response pathways and alter gene expression patterns in other ways (23,25,45,60).One of the known "side effects" of ribosome-targeting antibiotics is inhibition of ribosome assembly. This effect was originally described for chloramphenicol: defective particles sedimenting more slowly than mature ribosomal subunits were observed in cells treated with this drug (19,29). Such particles contain precursor forms of rRNA and an incomplete set of ribosomal proteins (1, 53). During chloramphenicol treatment, ribosomal proteins are produced in nonstoichiometric amounts (20). In addition, the equilibrium between the production of rRNA and ribosomal proteins is upset, and rRNA is expressed in excess (30,37,49). It has been proposed that this unbalanced synthesis of components is responsible for the chloramphenicol-induced defects in ribosomal assembly (21).More recently, Champney and colleagues suggested that several other inhibitors of protein synthesis stall the assembly of ribosomal subunits by binding to the respective precursor particles. The drugs proposed to have such an effect included macrolides and ketolides (10,11,15,35,59), streptogramin B (16), lincosamides (16), aminoglycosides (36), evernimicin (14), linezolid (12), and pleuromutilins (13). However, the indirect mechanism of assembly inhibition cannot be excluded for any of these drugs.To investigate the mechanism by which ribosome assembly is inhibited, we chose two inhibitors of the 50S subunit, erythromycin and chloramphenicol, and carried out experiments designed to differentiate between the two alternative hypotheses: (i) direct inhibition due to the binding of antibiotics to the precursor particles and (ii) indirect inhibition, when an imbalance in the production of c...

“…It has a complex mode of action with inhibition of translation and 50S ribosomal subunit formation. This dual inhibitory effect differentiated retapamulin from other bacterial protein synthesis inhibitors, such as macrolides and ketolides (1). Retapamulin acts at a site distinct from other antimicrobial agents, preventing the development of cross-resistance (2).…”

mentioning

confidence: 99%

In Vitro Activity of Retapamulin against Staphylococcus aureus Resistant to Various Antimicrobial Agents

Saravolatz

Pawlak

Saravolatz

et al. 2013

Retapamulin and six other antimicrobial agents were evaluated against 155 methicillin-resistant Staphylococcus aureus (MRSA) isolates, including strains resistant to vancomycin, linezolid, daptomycin, and mupirocin by microdilution tests. Time-kill assays were performed against representative MRSA, vancomycin-intermediate S. aureus (VISA), and vancomycin-resistant S. aureus (VRSA) isolates. Retapamulin and mupirocin demonstrated MIC 90 s of 0.12 g/ml and 8 g/ml, respectively, with resistance seen in 2.6% and 10% of isolates, respectively. Retapamulin maintained good activity against 94% (15/16) of mupirocin-resistant isolates.