Resistance to Quinupristin-Dalfopristin Due to Mutation of L22 Ribosomal Protein inStaphylococcus aureus

Abstract

The mechanism of resistance to the streptogramin antibiotics quinupristin and dalfopristin was studied in a Staphylococcus aureus clinical isolate selected under quinupristin-dalfopristin therapy, in four derivatives of S. aureus RN4220 selected in vitro, and in a mutant selected in a model of rabbit aortic endocarditis. For all strains the MICs of erythromycin, quinupristin, and quinupristin-dalfopristin were higher than those for the parental strains but the MICs of dalfopristin and lincomycin were similar. Portions of genes for domains II and V of 23S rRNA and the genes for ribosomal proteins L4 and L22 were amplified and sequenced. All mutants contained insertions or deletions in a protruding ␤ hairpin that is part of the conserved C terminus of the L22 protein and that interacts with 23S rRNA. Susceptible S. aureus RN4220 was transformed with plasmid DNA encoding the L22 alteration, resulting in transformants that were erythromycin and quinupristin resistant. Synergistic ribosomal binding of streptogramins A and B, studied by analyzing the fluorescence kinetics of pristinamycin I A -ribosome complexes, was abolished in the mutant strain, providing an explanation for quinupristin-dalfopristin resistance.Streptogramin antibiotics are a mixture of two classes of chemically distinct components, designated streptogramins A and B. Quinupristin-dalfopristin is a semisynthetic injectable streptogramin, a mixture of quinupristin and dalfopristin, which are semisynthetic derivatives of pristinamycin I A (PI A ; streptogramin B) and pristinamycin II A (PII A ; streptogramin A), respectively. The binding of these factors to the 50S ribosomal subunit causes inhibition of protein synthesis. Alone, each factor has a moderate bacteriostatic activity, but the combination can display a bactericidal synergistic effect, which has been attributed to the synergistic binding of the factors to their ribosomal target site (11).Quinupristin-dalfopristin is active against a wide range of gram-positive organisms including methicillin-resistant staphylococci and vancomycin-resistant Enterococcus faecium (33). Since streptogramins A and B are chemically unrelated and have different binding sites, the mechanisms of resistance to these two streptogramins are different. Resistance to each component of the streptogramins in both staphylococci and enterococci has been reported (13, 32). The most common type of resistance to streptogramin B antibiotics is related to the production of ribosomal methylases encoded by erm genes. Resistance results from decreased component B binding to the ribosome. Cross-resistance between streptogramins B and all macrolides and lincosamides occurs because these antimicrobials have overlapping binding sites, yielding the so-called macrolide-lincosamide-streptogramin B (MLS B ) phenotype. The synergistic inhibitory activity of the two streptogramin components is conserved even when the 23S rRNA is modified by an Erm methylase although the bactericidal activity of the streptogramin combination is altered. By contr...

Structural insights into species-specific features of the ribosome from the pathogen Staphylococcus aureus

“…Point mutations, deletions, and insertions in the uL22 hairpin loop that is part of the exit tunnel wall in residues R80-S108 in S. aureus confer resistance to erythromycin, Synercid, and telithromycin, although its location is too far to allow direct chemical interactions with the bound drugs (18,19). Importantly, similar resistance mutations were also observed in additional bacterial species.…”

“…Nevertheless, the epidemiology of S. aureus is increasing (11). Resistance mutations in S. aureus are also associated with ribosomal protein (rProtein) uL3, located in proximity to the PTC, as well as with uL4 and uL22 rProteins, whose segments are exposed in the exit tunnel (12)(13)(14)(15)(16)(17)(18)(19)(20).…”

Activity of a New Oral Streptogramin, XRP2868, against Gram-Positive Cocci Harboring Various Mechanisms of Resistance to Streptogramins

“…Some streptogramin-resistant strains were described previously, and others were constructed for this study. They were obtained either by cloning determinants of resistance on multicopy vectors pAT392 and pJIM2246 (2, 4) or by in vitro mutation of susceptible S. aureus, S. pneumoniae, and Streptococcus gordonii strains or transformation of S. pneumoniae CP1000 or S. gordonii strain Challis (4,6,15,23). In some constructs, resistance genes were combined.…”

LB11058, a New Cephalosporin with High Penicillin-Binding Protein 2a Affinity and Activity in Experimental Endocarditis Due to Homogeneously Methicillin-Resistant Staphylococcus aureus

“…This has resulted in a steady escalation of drug resistance. The organism proved capable of accumulating resistance mechanisms to virtually all clinically available compounds, including the entire beta-lactam family, the recent anti-gram-positive quinolones, and the streptogramin and oxazolidinone families, as well as nonexperimental last-resort drugs such as glycopeptides (4,11,17,24,25,28). Today, S. aureus represents a major risk to public health (1).…”