Growth of Staphylococcus aureus with Nafcillin In Vitro Induces  -Toxin Production and Increases the Lethal Activity of Sterile Broth Filtrates in a Murine Model

Abstract

The morbidity and mortality of Staphylococcus aureus infections remain high despite antibiotic therapy. To investigate further the observation that penicillins increase the hemolytic activity of staphylococcal cultures, 37 strains were grown in broth with and without subinhibitory nafcillin. Nafcillin stimulated hemolytic activity in nafcillin-susceptible and -resistant isolates. Sterile broth filtrates of nafcillin-associated cultures injected intraperitoneally in mice were more rapidly lethal than filtrates of the same strain grown without nafcillin. Lethality was neutralized by anti-alpha-toxin antisera. DNA-RNA hybridization revealed a nafcillin-associated increase in alpha-toxin mRNA during the postexponential growth phase after the activation of agr. Isolates grown in slightly inhibitory nafcillin concentrations had more alpha-toxin mRNA than did nafcillin-free cultures, whereas agr RNAIII levels were comparable. This suggests that nafcillin-induced alpha-toxin production is not entirely attributable to agr. A supplemental regulatory mechanism may be involved.

Induction of Fibronectin-Binding Proteins and Increased Adhesion of Quinolone-ResistantStaphylococcus aureusby Subinhibitory Levels of Ciprofloxacin

“…A few recent studies indicate that exposure of S. aureus to subinhibitory concentrations of some antibiotics may trigger in this pathogen a paradoxical increase in some of its virulence factors (1,21,35). Sub-MIC levels of ␤-lactams, in particular nafcillin, were shown to induce hla gene expression and increase alpha-toxin production in S. aureus (21,35).…”

“…Sub-MIC levels of ␤-lactams, in particular nafcillin, were shown to induce hla gene expression and increase alpha-toxin production in S. aureus (21,35). We recently reported that an isogenic fluoroquinolone-resistant grlA gyrA double mutant of S. aureus NCTC8325 grown in the presence of subinhibitory concentrations of ciprofloxacin expressed increased levels of FnBPs and showed a significantly higher attachment to fibronectin-coated polymer surfaces (1).…”

“…Subinhibitory concentrations of antibiotics may downregulate or upregulate specific adhesins as well as other virulence-associated determinants of S. aureus such as FnBPs (39,40), collagen-binding protein (2), or alpha-toxin (21,35). On the other hand, the acquisition of single or multiple antibiotic resistance determinants by S. aureus may also modulate expression of surface proteins.…”

Characterization of Alpha-Toxin hla Gene Variants, Alpha-Toxin Expression Levels, and Levels of Antibody to Alpha-Toxin in Hemodialysis and Postsurgical Patients with Staphylococcus aureus Bacteremia

“…Assessment of in vitro alpha-toxin production was done by quantitative analysis of rabbit red blood cell (RBC) lysis as previously described by our group (43) and others (44,45). Briefly, 10 ml of tryptic soy broth (TSB; Becton Dickinson, Sparks, MD) in a 50-ml Falcon tube was inoculated with a loopful of culture from a fresh plate of each strain and incubated at 37°C and 220 rpm for overnight culture.…”

“…This is an important factor to consider, because the antibiotic used could have a direct impact on virulence factor expression, including alpha-toxin. For example, studies have demonstrated that protein synthesis inhibitor antibiotics suppress expression of virulence factors like TSST-1, alpha-toxin, and coagulase in S. aureus isolates (59)(60)(61), while the cell wall-acting antibiotics have either no effect or enhance production of extracellular virulence factors (44,62). Second, the matched S. aureus isolates and serum samples were collected only after the subjects had experienced clinical symptoms for several days (average of 2 days [range, 0 to 30 days]) and had presented to the attending physician.…”