Virulence factor expression by Gram-positive cocci exposed to subinhibitory concentrations of linezolid

Abstract

Linezolid is a new oxazolidinone with potent antibacterial activity against Gram-positive cocci; it uniquely inhibits bacterial translation through inhibition of 70S initiation complex formation. The effects of sub-growth-inhibitory concentrations of linezolid on the expression of various structural and soluble virulence factors of Staphylococcus aureus and Streptococcus pyogenes were examined. For S. aureus, strains Wood 46 and Cowan 1 (NCTC 8532) were used to measure protein A, coagulase, alpha-haemolysin (hla) and delta-haemolysin (hld). For S. pyogenes, strain NCTC 9994 was used to measure M protein, streptolysin O (SLO) and DNase. Coagulase was assayed by clotting of citrated rabbit plasma, and hla, hld and SLO by lysis of rabbit, human and horse erythrocytes, respectively. Protein A and M protein were measured indirectly using bacterial susceptibility to phagocytic ingestion of radiolabelled bacteria by human neutrophils. When S. aureus was grown in 1/2, 1/4 and 1/8 MIC, linezolid, coagulase, hla and hld production were impaired. Susceptibility to phagocytosis was changed by growth in the presence of 1/2 MIC linezolid compared with that in its absence (50.8 +/- 4.1% versus 38.9 +/- 2.9%; P <or= 0.05). When S. pyogenes was grown in 1/2, 1/4 and 1/8 MIC linezolid, SLO and DNase production were impaired compared with that of bacteria grown in the absence of the drug; its susceptibility to phagocytosis was also increased (52.8% bacteria ingested versus 37.5%; P <or= 0.05). A reduction in virulence factor expression at sub-MIC linezolid concentrations may be of benefit in the treatment of Gram-positive infections.

Linezolid: The First Oxazolidinone Antimicrobial

“…As is true for the macrolides, subinhibitory concentrations of linezolid have been shown to inhibit the expression of virulence factors by staphylococci and streptococci (19). Specifically, subinhibitory concentrations of the drug decrease hemolysin and coagulase production by Staphylococcus aureus and impair streptolysin O and DNAase production in vitro by streptococci.…”

“…Specifically, subinhibitory concentrations of the drug decrease hemolysin and coagulase production by Staphylococcus aureus and impair streptolysin O and DNAase production in vitro by streptococci. Moreover, subinhibitory concentrations of the drug potentiate the susceptibility of Staphylococcus aureus and Streptococcus pyogenes to phagocytosis by human neutrophils (19). The exact clinical correlate of these in vitro findings remains to be determined.…”

Neutrophilia-Inducing Deferoxamine in Mice Infected with &lt;i&gt;Staphylococcus aureus&lt;/i&gt;

“…Each strain of S. aureus was inoculated to these media and incubated at 37˚C. After overnight incubation, doubling dilutions of culture supernatant centrifuged at 3000 rpm to remove bacteria, were made in diluent [phosphate-bufferedsaline (PBS), pH 7.1] and these used for quantitative measurements of virulence factor production [8].…”

“…The endpoint could be assessed accurately by measuring the number of intact RBCs using haemocytometer slide. A similar technique was used to measure beta-and delta-haemolysin, except that sheep erythrocytes were used as target cells for beta-haemolysin and human erythrocytes were used as target cells for delta-haemolysin [8].…”

“…Doubling dilutions of culture supernatant were made in diluent comprising PBS and 10% v/v nutrient broth, and an equal volume of 1/10 v/v citrated rabbit plasma was added. Clotting of the plasma after 4 hr of incubation at 37˚C indicated the presence of coagulase; the titre was taken as the highest dilution to produce a measurable clot [8].…”