Efficacy of trovafloxacin, a new quinolone antibiotic, in experimental staphylococcal endocarditis due to oxacillin-resistant strains

In vitro activities of the Rx-01 oxazolidinones against hospital and community pathogens

Rx-01_423 and Rx-01_667 are two members of the family of oxazolidinones that were designed using a combination of computational and medicinal chemistry and conventional biological techniques. The compounds have a two- to eightfold-improved potency over linezolid against serious gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), multidrug-resistant streptococci, and vancomycin-resistant enterococci. This enhanced potency extends to the coverage of linezolid-resistant gram-positive microbes, especially multidrug-resistant enterococci and pneumococci. Compounds from this series expand the spectrum compared with linezolid to include fastidious gram-negative organisms like Haemophilus influenzae and Moraxella catarrhalis. Like linezolid, the Rx-01 compounds are bacteriostatic against MRSA and enterococci but are generally bactericidal against S. pneumoniae and H. influenzae.

Human immunoglobulin G recognizing fibrinogen-binding surface proteins is protective against both Staphylococcus aureus and Staphylococcus epidermidis infections in vivo

A human donor-selected immunoglobulin G for intravenous injection (IGIV) product with elevated titers against the staphylococcal fibrinogen-binding MSCRAMM proteins ClfA and SdrG (INH-A21) was tested in vitro and in vivo. INH-A21 contained a significantly increased ability to inhibit the fibrinogen-binding activity of recombinant forms of both ClfA and SdrG. Evaluation of the opsonizing potential of INH-A21 was evaluated using fluorescently labeled bacteria; this assay indicated an increase in phagocytic activity compared to normal IGIV. The prophylactic efficacy of INH-A21 against an intraperitoneal challenge of methicillin-resistant Staphylococcus epidermidis (MRSE) was evaluated in a neonatal rat model. INH-A21 was also evaluated for prophylactic and therapeutic efficacy in a rabbit model of catheter-induced aortic valve infective endocarditis caused by either MRSE or methicillin-resistant Staphylococcus aureus (MRSA). Results from the in vivo models demonstrated potent prophylactic and therapeutic efficacy against both MRSE and MRSA. These data suggest that INH-A21 may be an important tool for the prevention and treatment of staphylococcal infections, especially in high-risk populations.

Anti-clumping factor A immunoglobulin reduces the duration of methicillin-resistant Staphylococcus aureus bacteremia in an experimental model of infective endocarditis

SA-IGIV is a human polyclonal immunoglobulin containing elevated levels of antibodies specific for the fibrinogen-binding MSCRAMM protein clumping factor A (ClfA). In vitro, SA-IGIV specifically recognized ClfA that was expressed on the surface of Staphylococcus aureus and inhibited bacterial adherence to immobilized human fibrinogen by >95%. Moreover, SA-IGIV efficiently opsonized ClfA-coated fluorescent beads and facilitated phagocytosis by human polymorphonuclear leukocytes. To determine its potential therapeutic efficacy, SA-IGIV was evaluated in combination with vancomycin in a rabbit model of catheter-induced aortic valve infective endocarditis (IE) caused by methicillin-resistant S. aureus (MRSA). The combination therapy was more effective than vancomycin alone in sterilizing all valvular vegetations when used therapeutically during early (12-h) IE. The combination therapy resulted in clearance of bacteremia that was significantly faster than that of vancomycin alone in animals with well-established (24-h) IE. Therefore, in both early and well-established MRSA IE, the addition of SA-IGIV to a standard antibiotic regimen (vancomycin) increased bacterial clearance from the bloodstream and/or vegetations.

Comparison of levofloxacin, alatrofloxacin, and vancomycin for prophylaxis and treatment of experimental foreign-body-associated infection by methicillin-resistant Staphylococcus aureus

The prophylactic and therapeutic activities of two fluoroquinolones, levofloxacin and alatrofloxacin (the L-Ala-L-Ala prodrug of trovafloxacin), were compared to those of vancomycin in two different experimental models of foreign-body-associated infections caused by methicillin-resistant but quinolone-susceptible Staphylococcus aureus (MRSA) isolates. In a guinea pig model of prophylaxis, subcutaneously implanted tissue cages were infected with 10(3) CFU of MRSA, which was a 100% infectious dose in control animals. A single dose of 50 mg of levofloxacin per kg of body weight, administered intraperitoneally 3 h before bacterial challenge, was more efficient than vancomycin for the prevention of infections in tissue cages with MRSA inocula of 10(4) and 10(5) CFU. In a rat model used to evaluate therapy of chronic tissue cage infection caused by MRSA, the efficacies of 7-day high-dose regimens of levofloxacin (100 mg/kg once a day [q.d.] or 50 mg/kg twice a day [b.i.d.]) or alatrofloxacin (50 mg/kg q.d.) were compared to the efficacy of vancomycin (50 mg/kg b.i.d.). Active levels of levofloxacin, trovafloxacin, and vancomycin were continuously present in tissue cage fluid, with the levels exceeding the minimal bactericidal concentrations for MRSA during therapy. The q.d. and b.i.d. regimens of levofloxacin had equivalent activities and were significantly (P < 0.05) more active than alatrofloxacin or vancomycin in decreasing the viable counts of MRSA in tissue cage fluids. No quinolone-resistant mutants emerged during therapy with either fluoroquinolone. The mechanisms explaining the inferior activity of alatrofloxacin compared to the activity of levofloxacin against chronic foreign-body-associated infections by MRSA are unknown.

Treatment of experimental staphylococcal endocarditis due to a strain with reduced susceptibility in vitro to vancomycin: efficacy of ampicillin-sulbactam

We evaluated several 3-day antimicrobial regimens in the treatment of experimental endocarditis caused by an oxacillin-resistant Staphylococcus aureus strain exhibiting intermediate susceptibility in vitro to vancomycin (VISA). Neither vancomycin alone nor trovafloxacin exhibited in vivo efficacy; addition of amikacin to vancomycin yielded a modest in vivo effect. In contrast, the combination of ampicillin and sulbactam was highly effective in vivo, causing a mean decrease in VISA vegetation densities of >5 log(10) CFU/g versus those of untreated controls.