Identification of (+)-erythro-mefloquine as an active enantiomer with greater efficacy than mefloquine against Mycobacterium avium infection in mice.

Infection caused by Mycobacterium avium is common in AIDS patients who do not receive treatment with highly active antiretroviral therapy (HAART) or who develop resistance to anti-HIV therapy. Mefloquine, a racemic mixture used for malaria prophylaxis and treatment, is bactericidal against M. avium in mice. MICs of (+)-erythro-, (-)-erythro-, (+)-threo-, and (-)-threo-mefloquine were 32 µg/ml, 32 µg/ml, 64 µg/ml, and 64 µg/ml, respectively. The postantibiotic effect for (+)-erythro-mefloquine was 36 h (MIC) and 41 h for a concentration of 4× MIC. The mefloquine postantibiotic effect was 25 h (MIC and 4× MIC). After baseline infection was established (7 days), the (+)- and (-)-isomers of the diastereomeric threo- and erythro-α-(2-piperidyl)-2,8-bis(trifluoromethyl)-4-quinolinemethanol were individually used to orally treat C57BL/6 bg(+)/bg(+) beige mice that were infected intravenously with M. avium. Mice were also treated with commercial mefloquine and diluent as controls. After 4 weeks of treatment, the mice were harvested, and the number of bacteria in spleen and liver was determined. Mice receiving (+)- or (-)-threo-mefloquine or (-)-erythro-mefloquine had numbers of bacterial load in tissues similar to those of untreated control mice at 4 weeks. Commercial mefloquine had a bactericidal effect. However, mice given the (+)-erythro-enantiomer for 4 weeks had a significantly greater reduction of bacterial load than those given mefloquine. Thus, (+)-erythro-mefloquine is the active enantiomer of mefloquine against M. avium and perhaps other mycobacteria.

EDP-420, a bicyclolide (bridged bicyclic macrolide), is active against Mycobacterium avium.

Infection caused by Mycobacterium avium complex (MAC) is common in patients with immunosuppression, such as AIDS, and deficiencies of gamma interferon and interleukin-12, as well as patients with chronic lung diseases. Treatment of MAC disease is limited since few drugs show in vivo activity. We tested a new bridged bicyclic macrolide, EDP-420, against MAC in vitro and in beige mice. EDP-420 was inhibitory in vitro at a concentration ranging from 2 to 8 microg/ml (MIC(50) of 4 microg/ml and MIC(90) of 8 microg/ml). In macrophages, EDP-420 was inhibitory at 0.5 microg/ml, suggesting that the drug concentrates intracellularly. Mice infected with macrolide-susceptible MAC strain 101 were given 100 mg of EDP-420/kg of body weight daily for 4 weeks and showed a significant reduction in the number of bacteria in both liver and spleen which was greater than the reduction observed with clarithromycin treatment at the same dose (P < 0.05). However, macrolide-resistant MAC 101 did not respond to EDP-420 treatment. A combination of EDP-420 with mefloquine was shown to be indifferent; mefloquine alone was active against macrolide-resistant MAC. The frequency of resistance to EDP-420 in MAC 101 was 10(-9), which is significantly less than the emergence of resistance to clarithromycin, approximately 10(-7) (P < 0.05). Further evaluation of EDP-420 in the treatment of MAC disease is warranted.

In vivo efficacy of phage therapy for Mycobacterium avium infection as delivered by a nonvirulent mycobacterium.

The emergence of mycobacteria resistant to currently available antimicrobial agents has become an important problem in modern medicine. Mycobacterium avium and M. tuberculosis are intracellular pathogens that replicate and survive within the mononuclear phagocytes. TM4 is a lytic mycobacteriophage that kills both extracellular M. avium and M. tuberculosis. When delivered by M. smegmatis transiently infected with TM4, it kills both M. avium and M. tuberculosis within RAW 264.7 macrophages. To evaluate the treatment of M. avium infection with phage in vivo, C57 BL/6 mice were infected with M. avium 109 and, 7 days later, treated either once or twice with TM4 phage (7.9 x 10(10) PFU/ml), M. smegmatis (4 x 10(8) cFU/ml), or M. smegmatis with TM4 phage delivered intravenously (i.v.). Treatment with TM4 phage alone or M. smegmatis without TM4 did not show a significant decrease in number of intracellular bacteria in the spleen compared with untreated control. In contrast, administration of M. smegmatis-TM4 resulted in a significant decrease in the number of M. avium in the spleen. However, 23% of bacteria recovered from treated mice were resistant to TM4. These in vivo studies confirmed the in vitro findings that an avirulent mycobacterium can be used as a carrier to deliver antimycobacterial phage intracellularly.

Genomic approach to identifying the putative target of and mechanisms of resistance to mefloquine in mycobacteria.

The emergence of mycobacterial resistance to multiple antimicrobials emphasizes the need for new compounds. The antimycobacterial activity of mefloquine has been recently described. Mycobacterium avium, Mycobacterium smegmatis, and Mycobacterium tuberculosis are susceptible to mefloquine in vitro, and activity was evidenced in vivo against M. avium. Attempts to obtain resistant mutants by both in vitro and in vivo selection have failed. To identify mycobacterial genes regulated in response to mefloquine, we employed DNA microarray and green fluorescent protein (GFP) promoter library techniques. Following mefloquine treatment, RNA was harvested from M. tuberculosis H37Rv, labeled with 32P, and hybridized against a DNA array. Exposure to 4x MIC resulted in a significant stress response, while exposure to a subinhibitory concentration of mefloquine triggered the expression of genes coding for enzymes involved in fatty acid synthesis, the metabolic pathway, and transport across the membrane and other proteins of unknown function. Evaluation of gene expression using an M. avium GFP promoter library exposed to subinhibitory concentrations of mefloquine revealed more than threefold upregulation of 24 genes. To complement the microarray results, we constructed an M. avium genomic library under the control of a strong sigma-70 (G13) promoter in M. smegmatis. Resistant clones were selected in 32 microg/ml of mefloquine (wild-type M. avium, M. tuberculosis, and M. smegmatis are inhibited by 8 microg/ml), and the M. avium genes associated with M. smegmatis resistant to mefloquine were sequenced. Two groups of genes were identified: one affecting membrane transport and one gene that apparently is involved in regulation of cellular replication.

Destroying the life and career of a valued physician-scientist who tried to protect us from plague: was it really necessary?

Thomas Campbell Butler, at 63 years of age, is completing the first year of a 2-year sentence in federal prison, following an investigation and trial that was initiated after he voluntarily reported that he believed vials containing Yersinia pestis were missing from his laboratory at Texas Tech University. We take this opportunity to remind the infectious diseases community of the plight of our esteemed colleague, whose career and family have, as a result of his efforts to protect us from infection by this organism, paid a price from which they will never recover.

A subinhibitory concentration of clarithromycin inhibits Mycobacterium avium biofilm formation.

Mycobacterium avium causes disseminated infection in immunosuppressed individuals and lung infection in patients with chronic lung diseases. M. avium forms biofilm in the environment and possibly in human airways. Antibiotics with activity against the bacterium could inhibit biofilm formation. Clarithromycin inhibits biofilm formation but has no activity against established biofilm.

SRI-286, a thiosemicarbazole, in combination with mefloquine and moxifloxacin for treatment of murine Mycobacterium avium complex disease.

Treatment of Mycobacterium avium disease remains challenging when macrolide resistance develops. We infected C57 beige mice and treated them with mefloquine, SRI-286, and moxifloxacin. SRI-286 (80 mg/kg) was bactericidal in the liver. Mefloquine plus moxifloxacin or mefloquine plus SRI-286 were better than mefloquine alone.

Thiosemicarbazole (thiacetazone-like) compound with activity against Mycobacterium avium in mice.

In vitro screening of thiacetazone derivatives indicated that two derivatives, SRI-286 and SRI-224, inhibited a panel of 25 Mycobacterium avium complex (MAC) isolates at concentrations of 2 micro g/ml or lower. In mice, SRI-224 and thiacetazone had no significant activity against the MAC in livers and spleens, but treatment with SRI-286 resulted in significant reduction of bacterial loads in livers and spleens. A combination of SRI-286 and moxifloxacin was significantly more active than single drug regimens in liver and spleen.

Mefloquine, moxifloxacin, and ethambutol are a triple-drug alternative to macrolide-containing regimens for treatment of Mycobacterium avium disease.

Macrolides are the core of effective drug regimens for the treatment of Mycobacterium avium complex (MAC) disease. Mefloquine (MFQ), moxifloxacin (MXF), and ethambutol (EMB), in combination, were evaluated against both clarithromycin-resistant (CLR-R) and CLR-susceptible (CLR-S) MAC; MFQ (40 mg/kg), MXF (100 mg/kg), or EMB (100 mg/kg/day) was given to mice for 4 weeks. MFQ was bactericidal, whereas MXF and EMB were bacteriostatic against both MAC 101 CLR-S and CLR-R. The combination of MFQ and EMB reduced (P<.05, for comparison with controls), and the combination of MFQ and MXF significantly reduced, the load of CLR-R in both the liver and the spleen. Treatment with all 3 drugs was associated with approximately 1-log reduction of CLR-R after 1 week, 2.1-log reduction of CLR-R after 4 weeks, and 2.17-log reduction in MAC/mL blood. Treatment of MAC 101 CLR-S strain had comparable results.

Therapy of sepsis.

The term 'sepsis' is often used synonymously with 'infection' or 'bacteremia'. Additional definitions, e.g. 'systemic inflammatory response syndrome', have been proposed. These terms have been employed to establish entry criteria for clinical trials of antibiotic therapy and adjunctive therapies. It may be appropriate to utilize these descriptions when initiating therapy of suspected bacterial infections, since culture confirmation is often not available for days after initial clinical presentation. Empiric antibiotic therapy is now the rule rather than the exception for febrile hospitalized patients. No antimicrobial agent is superior for all major clinical situations and thus history and physical examination are critical factors which guide the clinician. Guidelines have been derived for the initial empiric management of serious infection. While these were initially refined for the immunocompromized host, they may be considered generally applicable for the hospitalized patient with a suspected serious systemic bacterial infection. Currently, monotherapy with agents such as cefepime, ceftazidime, imipenem/cilastatin and meropenem has been sanctioned on the basis of their broad antimicrobial coverage and stability to clinically important beta-lactamases (although there is considerable variation from one compound to another). Perception of local epidemiologic patterns is a major factor in the selection of initial antibacterial therapy for hospital-acquired infection.

Antibiotic Update for the Surgeon.

The number of antimicrobial agents that have been introduced into clinical practice continues to increase. This development, however, is not unique to the antibiotic field. All one has to do is to look at the burgeoning number of compounds for antiinflammatory or cardiovascular indications to recognise that the pharmaceutical industry continues to provide us with new compounds of increased potency and broadened therapeutic applicability. On the other hand, not all new drug introductions represent clinical breakthroughs. Some agents can be, quite frankly, classified as 'me too' drugs. Nonetheless, even a fairly simple congener could be a welcome addition to the therapeutic armamentarian if it is safer, less toxic, cheaper, and more convenient to use than previously available therapy.