Antibacterial oxazolidinones possessing a novel C-5 side chain. (5R)-trans-3-[3-Fluoro-4- (1-oxotetrahydrothiopyran-4-yl)phenyl]-2- oxooxazolidine-5-carboxylic acid amide (PF-00422602), a new lead compound.

Oxazolidinones possessing a C-5 carboxamide functionality (reverse amides) represent a new series of compounds that block bacterial protein synthesis. These reverse amides also exhibited less potency against monoamine oxidase (MAO) enzymes and thus possess less potential for the side effects associated with MAO inhibition. The title compound (14) showed reduced in vivo myelotoxicity compared to linezolid in a 14-day safety study in rats, potent in vivo efficacy in murine systemic infection models, and excellent pharmacokinetic properties.

In vitro and in vivo activities of PD 0305970 and PD 0326448, new bacterial gyrase/topoisomerase inhibitors with potent antibacterial activities versus multidrug-resistant gram-positive and fastidious organism groups.

PD 0305970 and PD 0326448 are new bacterial gyrase and topoisomerase inhibitors (quinazoline-2,4-diones) that possess outstanding in vitro and in vivo activities against a wide spectrum of bacterial species including quinolone- and multidrug-resistant gram-positive and fastidious organism groups. The respective MICs (microg/ml) for PD 0305970 capable of inhibiting>or=90% of bacterial strains tested ranged from 0.125 to 0.5 versus staphylococci, 0.03 to 0.06 versus streptococci, 0.25 to 2 versus enterococci, and 0.25 to 0.5 versus Moraxella catarrhalis, Haemophilus influenzae, Listeria monocytogenes, Legionella pneumophila, and Neisseria spp. PD 0326448 MIC90s were generally twofold higher versus these same organism groups. Comparative quinolone MIC90 values were 4- to 512-fold higher than those of PD 0305970. In testing for frequency of resistance, PD 0305970 and levofloxacin showed low levels of development of spontaneous resistant mutants versus both Staphylococcus aureus and Streptococcus pneumoniae. Unlike quinolones, which target primarily gyrA and parC, analysis of resistant mutants in S. pneumoniae indicates that the likely targets of PD 0305970 are gyrB and parE. PD 0305970 demonstrated rapid bactericidal activity by in vitro time-kill testing versus streptococci. This bactericidal activity carried over to in vivo testing, where PD 0305970 and PD 0326448 displayed outstanding Streptococcus pyogenes 50% protective doses (PD50s) (oral dosing) of 0.7 and 3.6 mg/kg, respectively (ciprofloxacin and levofloxacin PD50s were>100 and 17.7 mg/kg, respectively). PD 0305970 was also potent in a pneumococcal pneumonia mouse infection model (PD50=3.2 mg/kg) and was 22-fold more potent than levofloxacin.

Development of a mouse model of induced Staphylococcus aureus infective endocarditis.

We developed a mouse model of Staphylococcus aureus infective endocarditis to evaluate the efficacy of experimental antibacterial compounds for this disease. Experimental infective endocarditis was produced in CD1 mice by intravenous challenge with approximately 6 log10 colony-forming units (CFU) of methicillin-sensitive (MSSA) SA-3529 or -resistant (MRSA) SA-2015 S. aureus 1 d after aortic valve trauma. Valve trauma was produced by introduction of an indwelling 32-gauge polyurethane catheter into the aortic valve via the left carotid artery. Histologic examination of MSSA- and MRSA-infected and catheterized aortic valve sections revealed neutrophilic inflammation and vegetative bacterial colonies encapsulated within fibrin along the aortic valves 1 d after infection. The MSSA or MRSA endocarditis was determined to be catheter-dependent based on catheterized mice exhibiting heart bacterial counts 4 orders of magnitude greater than those seen for noncatheterized mice. The model was validated by using a 3-d regimen of vancomycin at exposures comparable to human dosing (500 microg x h/ml). Vancomycin treatment produced statistically significant reductions of 3.4 and 3.1 log10 CFU/heart for MSSA and MRSA, respectively, relative to controls. This mouse model of endocarditis shows promise in evaluating the predictive efficacy of antibiotics for S. aureus infective endocarditis.

Lesions in teichoic acid biosynthesis in Staphylococcus aureus lead to a lethal gain of function in the otherwise dispensable pathway.

An extensive study of teichoic acid biosynthesis in the model organism Bacillus subtilis has established teichoic acid polymers as essential components of the gram-positive cell wall. However, similar studies pertaining to therapeutically relevant organisms, such as Staphylococcus aureus, are scarce. In this study we have carried out a meticulous examination of the dispensability of teichoic acid biosynthetic enzymes in S. aureus. By use of an allelic replacement methodology, we examined all facets of teichoic acid assembly, including intracellular polymer production and export. Using this approach we confirmed that the first-acting enzyme (TarO) was dispensable for growth, in contrast to dispensability studies in B. subtilis. Upon further characterization, we demonstrated that later-acting gene products (TarB, TarD, TarF, TarIJ, and TarH) responsible for polymer formation and export were essential for viability. We resolved this paradox by demonstrating that all of the apparently indispensable genes became dispensable in a tarO null genetic background. This work suggests a lethal gain-of-function mechanism where lesions beyond the initial step in wall teichoic acid biosynthesis render S. aureus nonviable. This discovery poses questions regarding the conventional understanding of essential gene sets, garnered through single-gene knockout experiments in bacteria and higher organisms, and points to a novel drug development strategy targeting late steps in teichoic acid synthesis for the infectious pathogen S. aureus.