The activities of linezolid, eperezolid, and PNU-100480 were evaluated in a murine model of tuberculosis. Approximately 107 viable Mycobacterium tuberculosis ATCC 35801 organisms were given intravenously to 4-week-old outbred CD-1 mice. In the first study, treatment was started 1 day postinfection and was given by gavage for 4 weeks. Viable cell counts were determined from homogenates of spleens and lungs. PNU-100480 was as active as isoniazid. Linezolid was somewhat less active than PNU-100480 and isoniazid. Eperezolid had little activity in this model. In the next two studies, treatment was started 1 week postinfection. A dose-response study was performed with PNU-100480 and linezolid (both at 25, 50, and 100 mg/kg of body weight). PNU-100480 was more active than linezolid, and its efficacy increased with an escalation of the dose. Subsequently, the activity of PNU-100480 alone and in combination with rifampin or isoniazid was evaluated and was compared to that of isoniazid-rifampin. The activity of PNU-100480 was similar to that of isoniazid and/or rifampin in the various combinations tested. Further evaluation of these oxazolidinones in the murine test system would be useful prior to the development of clinical studies with humans.

A series of substituted pyrazinoic acid esters has been prepared and examined for their in vitro activity against Mycobacterium avium and Mycobacterium kansasii as well as Mycobacterium tuberculosis. Modification of both the pyrazine nucleus and the ester functionality have been very successful in expanding the activity of pyrazinamide to include M. avium and M. kansasii, organisms normally not susceptible to pyrazinamide. Several of these compounds have activities 100-1000-fold greater than that of pyrazinamide against M. tuberculosis.

We have investigated the possibility that the generation of hydrogen peroxide (H2O2) by spermatozoa plays a physiological role during capacitation. Capacitation is defined as the incubation period required for fertilization in mammals. Capacitation culminates in an exocytotic event, the acrosome reaction (AR). Mammalian sperm generate H2O2 during aerobic incubation and do not contain catalase, the enzyme that promotes scavenging of H2O2. In the present work we show that added catalase inhibited the AR, while glucose oxidase (GO), an enzyme that generates H2O2, accelerated the onset of the AR. Direct addition of H2O2 also stimulated the AR; catalase inhibited both the stimulation by GO and by H2O2. The onset of the AR was always preceded by the appearance of hyperactivated motility. The stimulation of the AR by H2O2 was manifest 1-2 h after the addition of H2O2. Catalase added at 3 h of incubation was less effective in inhibiting the AR than catalase added at the beginning. Incubation of sperm with catalase prevented the induction of the AR by the membrane-perturbing lipid, lysophosphatidyl choline. Taken together, these results suggest that H2O2 produced by hamster sperm plays a significant role during capacitation, possibly in membrane reorganization to facilitate the fusion that takes place during exocytosis of the acrosomal contents.

The activity of levofloxacin (LEV) Ofloxacin (OFL), a pyridonecarboxylic acid derivative of nalidixic acid, has an asymmetric center at the C-3 position of the oxazine ring (12). This fluoroquinolone exists as a racemic mixture (12). Levofloxacin (LEV), the l-enantiomer, has twoto fourfold greater in vitro activity than OFL against a variety of gram-positive and gram-negative pathogens (3,16,20). It is also more active than OFL in murine models of systemic infection with Staphylococcus aureus and Pseudomonas aeruginosa (2).The MICs of OFL for Mycobacterium tuberculosis determined radiometrically in 7H12 broth range from 0.5 to 2.0 ,ug/ml (6). The dose-dependent activity of OFL has been demonstrated in a murine model of tuberculosis (19). OFL at 300 mg/kg of body weight has good activity, but OFL at 150 mg/kg has only modest activity (19). The area under the concentration-time curve for OFL in mice receiving the drug at 150 mg/kg is similar to that in humans receiving a single 600-mg dose (8). Although OFL dosages of as high as 800 mg given once per day have been well tolerated (22), the role of OFL in the treatment of tuberculosis has not yet been defined (7,10,23).The MICs of LEV for M. tuberculosis (n = 12) determined radiometrically are twofold lower than those of OFL (range, 0.25 to 1.0 ,ug/ml) (14). The purpose of the present study was to evaluate the activity of LEV in a murine model of tuberculosis. The activity of LEV was compared with those of the first-line antituberculosis agents and those of OFL and sparfloxacin (SPA).

The activity of pyrazinamide (PZA) against eight isolates of Mycobacterium tuberculosis in a murine infection model was evaluated. M. tuberculosis isolates with various degrees of in vitro susceptibility to PZA (MIC range, 32 to > 2,048 micrograms/ml) were used. Four-week-old female mice were infected intravenously with approximately 10(7) viable M. tuberculosis organisms. PZA at 150 mg/kg of body weight was started 1 day postinfection and given 5 days/week for 4 weeks. Infected but untreated mice were compared with PZA-treated mice. Mice were sacrificed at the completion of the treatment period, and viable cell counts were determined from homogenates of spleens and right lungs. PZA had activity in the murine test system against M. tuberculosis isolates for which the MICs were < or = 256 micrograms/ml. However, there was an inconsistent correlation between the absolute MICs and the reductions in organ viable cell counts. Studies with drug-resistant M. tuberculosis isolates with an isogenic background would improve evaluation of drug efficacy in the murine test system. Further evaluation of antimycobacterial agents against monodrug-resistant isolates will provide data that will be useful for development of algorithms for treatment of infection with drug-resistant organisms.