Clindamycin suppresses virulence expression in inducible clindamycin-resistant Staphylococcus aureus strains.

Clindamycin is a protein synthesis inhibitory agent that has the ability to suppress the expression of virulence factors in Staphylococcus aureus. Recent guidelines recommend the use of clindamycin for the treatment of toxin-mediated infections. Clindamycin modulates virulence expression at sub-inhibitory concentrations (sub-MICs) in clindamycin-susceptible S. aureus strains but previous report shown that this effect was supressed for constitutive clindamycin resistant strains. However, no data are currently available on the impact of clindamycin at sub-MICs on the virulence of inducible clindamycin-resistant S. aureus strains. Here, we show that sub-MICs of clindamycin decrease Panton-Valentine leucocidin, toxic-shock-staphylococcal toxin (TSST-1) and alpha-haemolysin (Hla) expression in six inducible clindamycin-resistant isolates cultivated in vitro in CCY medium. These results suggest that the clindamycin anti-toxin effect is retained for inducible clindamycin-resistant S. aureus isolates; therefore, its usage should be considered within the treatment regimen of toxin related infections for inducible clindamycin-resistant S. aureus.

In vivo effect of flucloxacillin in experimental endocarditis caused by mecC-positive staphylococcus aureus showing temperature-dependent susceptibility in vitro.

Methicillin-resistant Staphylococcus aureus (MRSA) carrying the mecC gene (mecC-MRSA) exhibited at 37°C MICs of oxacillin close to those of methicillin-susceptible S. aureus (MSSA). We investigated whether at this temperature, mecC-MRSA strains respond to flucloxacillin treatment like MSSA strains, using a rat model of endocarditis. Flucloxacillin (human-like kinetics of 2 g intravenously every 6 h) cured 80 to 100% of aortic vegetations infected with five different mecC-MRSA strains. These results suggest that mecC-MRSA infections may successfully respond to treatment with ß-lactams.

Dual impact of live Staphylococcus aureus on the osteoclast lineage, leading to increased bone resorption.

BACKGROUND: Bone and joint infection, mainly caused by Staphylococcus aureus, is associated with significant morbidity and mortality, characterized by severe inflammation and progressive bone destruction. Studies mostly focused on the interaction between S. aureus and osteoblasts, the bone matrix-forming cells, while interactions between S. aureus and osteoclasts, the only cells known to be able to degrade bone, have been poorly explored. METHODS: We developed an in vitro infection model of primary murine osteoclasts to study the direct impact of live S. aureus on osteoclastogenesis and osteoclast resorption activity. RESULTS: Staphylococcal infection of bone marrow-derived osteoclast precursors induced their differentiation into activated macrophages that actively secreted proinflammatory cytokines. These cytokines enhanced the bone resorption capacity of uninfected mature osteoclasts and promoted osteoclastogenesis of the uninfected precursors at the site of infection. Moreover, infection of mature osteoclasts by live S. aureus directly enhanced their ability to resorb bone by promoting cellular fusion. CONCLUSIONS: Our results highlighted two complementary mechanisms involved in bone loss during bone and joint infection, suggesting that osteoclasts could be a pivotal target for limiting bone destruction.

Prompt and successful toxin-targeting treatment of three patients with necrotizing pneumonia due to Staphylococcus aureus strains carrying the Panton-Valentine leukocidin genes.

Three patients with extensive necrotizing pneumonia due to Panton-Valentine leukocidin-positive Staphylococcus aureus strains and with aggravating factors (leukopenia count of less than 3x10(9)/liter in all three cases and hemoptysis in two cases) were successfully treated with toxin-suppressing agents introduced rapidly after hospital admission.