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Medline ® Abstracts for References 64,65

of 'Treatment of community-acquired pneumonia in adults who require hospitalization'

64
TI
Subinhibitory concentrations of linezolid reduce Staphylococcus aureus virulence factor expression.
AU
Bernardo K, Pakulat N, Fleer S, Schnaith A, Utermöhlen O, Krut O, Müller S, Krönke M
SO
Antimicrob Agents Chemother. 2004;48(2):546.
 
The influence of the antibiotic linezolid on the secretion of exotoxins by Staphylococcus aureus was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis combined with matrix-assisted laser desorption ionization-time of flight mass spectrometry and Western blot analysis. S. aureus suspensions were treated with grading subinhibitory concentrations of linezolid (12.5, 25, 50, and 90% of MIC) at different stages of bacterial growth (i.e., an optical density at 540 nm [OD(540)]of 0.05 or 0.8). When added to S. aureus cultures at an OD(540) of 0.05, linezolid reduced in a dose-dependent manner the secretion of specific virulence factors, including staphylococcal enterotoxin A (SEA) and SEB, bifunctional autolysin, autolysin, protein A, and alpha- and beta-hemolysins. In contrast, other presumably nontoxic exoproteins remained unchanged or even accumulated in supernatants in the presence of linezolid at a 90% MIC. Similarly, when added at OD(540) of 0.8, that is, after quorum sensing, linezolid reduced the release of virulence factors, whereas the relative abundance of nontoxic exoproteins such as triacylglycerol lipase, glycerol ester hydrolase, DnaK, or translation elongation factor EF-Tu was found to be increased. Consistently, linezolid reduced in a dose-dependent manner the tumor necrosis factor-inducing activity secreted by S. aureus into the culture supernatants. The results of our study suggest that the expression of virulence factors in S. aureus is especially sensitive to the inhibition of protein synthesis by linezolid, which should be an advantage in the treatment of infections with toxin-producing S. aureus.
AD
Institute for Medical Microbiology, Immunology, and Hygiene, Medical Center, University of Cologne, Cologne, Germany.
PMID
65
TI
Impact of antibiotics on expression of virulence-associated exotoxin genes in methicillin-sensitive and methicillin-resistant Staphylococcus aureus.
AU
Stevens DL, Ma Y, Salmi DB, McIndoo E, Wallace RJ, Bryant AE
SO
J Infect Dis. 2007;195(2):202. Epub 2006 Dec 18.
 
Extracellular protein toxins contribute to the pathogenesis of a wide variety of Staphylococcus aureus infections. The present study investigated the effects that cell-wall active antibiotics and protein-synthesis inhibitors have on transcription and translation of genes for Panton-Valentine leukocidin, alpha-hemolysin, and toxic-shock syndrome toxin 1, in both methicillin-sensitive and methicillin-resistant S. aureus. Subinhibitory concentrations of nafcillin induced and prolonged mRNA for Panton-Valentine leukocidin, alpha-toxin, and toxic-shock syndrome toxin 1 and increased toxin production. In contrast, clindamycin and linezolid markedly suppressed translation, but not transcription, of toxin genes. These results suggest (1) that protein-synthesis inhibition is an important consideration in the selection of antimicrobial agents to treat serious infections caused by toxin-producing gram-positive pathogens and (2) that, by inducing and enhancing toxin production, inadvertent use of beta-lactam antibiotics to treat methicillin-resistant S. aureus infections may contribute to worse outcomes.
AD
Veterans Affairs Medical Center, Boise, ID 83702, USA. dlsteven@mindspring.com
PMID