A noninvasive, real-time detection technology was validated for qualitative and quantitative antimicrobial treatment applications. The lux gene cluster of Photorhabdus luminescens was introduced into an Escherichia coli clinical isolate, EC14, on a multicopy plasmid. This bioluminescent reporter bacterium was used to study antimicrobial effects in vitro and in vivo, using the neutropenic-mouse thigh model of infection. Bioluminescence was monitored and measured in vitro and in vivo with an intensified charge-coupled device (ICCD) camera system, and these results were compared to viable-cell determinations made using conventional plate counting methods. Statistical analysis demonstrated that in the presence or absence of antimicrobial agents (ceftazidime, tetracycline, or ciprofloxacin), a strong correlation existed between bioluminescence levels and viable cell counts in vitro and in vivo. Evaluation of antimicrobial agents in vivo could be reliably performed with either method, as each was a sound indicator of therapeutic success. Dose-dependent responses could also be detected in the neutropenic-mouse thigh model by using either bioluminescence or viable-cell counts as a marker. In addition, the ICCD technology was examined for the benefits of repeatedly monitoring the same animal during treatment studies. The ability to repeatedly measure the same animals reduced variability within the treatment experiments and allowed equal or greater confidence in determining treatment efficacy. This technology could reduce the number of animals used during such studies and has applications for the evaluation of test compounds during drug discovery.

The first potent inhibitors of glutamate racemase (MurI) enzyme that show whole cell antibacterial activity are described. Optically pure 4-substituted D-glutamic acid analogues with (2R,4S) stereochemistry and bearing aryl-, heteroaryl-, cinnamyl-, or biaryl-methyl substituents represent a novel class of glutamate racemase inhibitors. Exploration of the D-Glu core led to the identification of lead compounds (-)-8 and 10. 2-Naphthylmethyl derivative 10 was found to be a potent competitive inhibitor of glutamate racemase activity (K(i) = 16 nM, circular dichroism assay; IC(50) = 0.1 microg/mL high-performance liquid chromatography (HPLC) assay). Thorough structure-activity relationship (SAR) studies led to benzothienyl derivatives such as 69 and 74 with increased potency (IC(50) = 0.036 and 0.01 microg/mL, respectively, HPLC assay). These compounds showed potent whole cell antibacterial activity against S. pneumoniae PN-R6, and good correlation with the enzyme assay. Compounds 69, 74 and biaryl derivative 52 showed efficacy in an in vivo murine thigh infection model against Streptococcus pneumoniae. Data described herein suggest that glutamate racemase may be a viable target for developing new antibacterial agents.

The pharmacokinetics and pharmacodynamics of oritavancin (LY333328), a glycopeptide antibiotic with concentration-dependent bactericidal activity against gram-positive pathogens, in a neutropenic-mouse thigh model of Staphylococcus aureus infection were studied. Plasma radioequivalent concentrations of oritavancin were determined by using [ 14 C]oritavancin at doses ranging from 0.5 to 20 mg/kg of body weight. Peak plasma radioequivalent concentrations after an intravenous dose were 7.27, 12.56, 69.29, and 228.83 g/ml for doses of 0.5, 1, 5, and 20 mg/kg, respectively. The maximum concentration of drug in serum (C max ) and the area under the concentration-time curve (AUC) increased linearly in proportion to the dose. Neither infection nor neutropenia was seen to affect the pharmacokinetics of oritavancin. Intravenous administration resulted in much higher concentrations in plasma than the concentrations obtained with subcutaneous administration. Single-dose dose-ranging studies suggested a sigmoid maximum effect (E max ) dose-response relationship, with a maximal effect evident at single doses exceeding 2 mg/kg. The oritavancin dose (stasis dose) that resulted in a 24-h colony count similar to the pretreatment count was 1.53 (standard error [SE], 0.35) mg/kg. The single oritavancin dose that resulted in 50% of maximal bacterial killing (ED 50 ) was 0.95 (SE, 0.20) mg/kg. Dose fractionation studies suggested that single doses of 0.5, 1, 2, 4, and 16 mg/kg appeared to have greater bactericidal efficacy than the same total dose subdivided and administered multiple times during the 24-h treatment period. When using an inhibitory E max model, C max appears to correlate better with bactericidal activity than do the time during which the concentration in plasma exceeds the MIC (T>MIC) and AUC. These data suggest that optimal oritavancin dosing strategies will require regimens that favor high C max concentrations rather than long periods during which unbound concentrations in plasma exceed the MIC.The recent emergence of enterococci and staphylococci with reduced susceptibility to vancomycin (16, 23) has highlighted the need for improved infection control measures (24) and the development of new antibiotic agents (20). Oritavancin, a semisynthetic glycopeptide derived from the N alkylation of the naturally occurring glycopeptide LY264826 (A82846B) (7), has a broad spectrum of activity against gram-positive cocci (25), including glycopeptide-resistant enterococci and Staphylococcus aureus strains with intermediate susceptibility to glycopeptides (1, 18). Oritavancin also displays several in vitro properties that distinguish it from vancomycin, including in vitro concentration-dependent bactericidal activity against S. aureus and enterococci (6,18,26,27) , Berlin, Germany, 1999, abstr. P191, 1999.The present study uses a neutropenic-mouse thigh model of S. aureus infection to characterize oritavancin pharmacokinetics in mice and explore the relationship between relevant pharmacodynamic indices (maximum concentration of...

An immunosuppressed rat model of Pneumocystis carinii pneumonia is described that utilizes simple, noninvasive intratracheal (i.t.) inoculation of cryopreserved parasites and results in development of severe P. carinii pneumonia within 5 weeks. This is an improvement over the most commonly used models of P. carinii pneumonia that rely on immune suppression to activate latent P. carinii infections and that often require 8 to 12 weeks to produce heavy infections of P. carinii. It is also less labor intensive than more recent models requiring surgical instillation of parasites. Our report describes a series of preliminary studies to select an appropriate strain of rat; to determine suitable methods for inducing uniform immunosuppression, P. carinii inoculation, and laboratory maintenance of P. carinii; and to determine effective animal husbandry methods for maintaining animals free from serious secondary infections. Results of our more detailed studies demonstrate that animals receiving two or three i.t. inoculations of approximately 106 cryopreserved P. carinii organisms have a predictable course of disease progression which includes moderate P. carinii infections within 3 weeks, severe P. carinii pneumonia in 5 weeks, and a high percentage of mortality due to P. carinii pneumonia in 6 weeks. Parasites were distributed evenly between the right and left lungs, regardless of the number of P. carinii inoculations administered. Non-P. carinii-inoculated immunosuppressed control rats maintained in microisolator cages remained free ofP. carinii, thus providing an important control that is missing from many P. carinii pneumonia models. Most non-P. carinii-inoculated control animals and P. carinii-inoculated rats treated with trimethoprim-sulfamethoxazole that were housed in open caging in the same room containing heavily infected animals had no detectable infections after 5 to 6 weeks of immunosuppression; however, some had a small number of P. carinii in their lungs. Because heavy, reproducible infections are achieved 5 weeks after i.t. inoculation, because few animals are lost to secondary infections, and because animals can be maintained as noninfected contemporaneous controls, this animal model is useful for the maintenance of P. carinii strains, for studies of the transmission and natural history of P. carinii, for the production of large numbers of organisms for laboratory studies, and for the evaluation of potential anti-P. carinii drugs.

Cyclic lipodepsipeptide compounds of the echinocandin class exhibit broad-spectrum antifungal activity and have been shown to be effective in the treatment of Pneumocystis carinii pneumonia in laboratory animal models. Previous studies have led investigators to propose that these compounds, active against fungal cell walls, are selectively active against the cyst forms of P. carinii. We demonstrate that a semisynthetic, water-soluble echinocandin analog, LY307853, is effective in reducing the number of all life cycle forms of P. carinii and is more effective in mice immunosuppressed with monoclonal antibody to L3T4+ cells than in mice immunosuppressed with dexamethasone. Treatment of P. carinii isolates with LY307853 in a short-term in vitro culture model resulted in cytoarchitectural alterations suggesting that this echinocandin may interfere with the export of surface glycoprotein and the formation of the tubular elements normally found on the surfaces of trophic forms. The cytoarchitectural changes in trophic forms treated in vitro with LY307853 were also observed in trophic forms in the lung tissue of rats treated with a closely related echinocandin analog, LY303366.

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