Activity of novel oxazolidinones against Nocardia brasiliensis growing within THP-1 macrophages

In Vitro Susceptibility Testing of Tedizolid against Isolates of Nocardia

There is a paucity of efficacious antimicrobials (especially oral) against clinically relevant species of Nocardia To date, all species of Nocardia have been susceptible to linezolid, the first commercially available oxazolidinone. Tedizolid is a new oxazolidinone with previously reported improved in vitro and in vivo (intracellular) potency against multidrug-resistant strains of Mycobacterium sp. and Nocardia brasiliensis Using the current Clinical and Laboratory Standards Institute-recommended broth microdilution method, 101 isolates of Nocardia spp., including 29 Nocardia cyriacigeorgica, 17 Nocardia farcinica, 13 Nocardia nova complex, 21 Nocardia brasiliensis, 5 Nocardia pseudobrasiliensis, and 5 Nocardia wallacei isolates and 11 isolates of less common species, were tested for susceptibility to tedizolid and linezolid. For the most common clinically significant species of Nocardia, tedizolid MIC₅₀ values were 0.25 μg/ml for N. nova complex, N. brasiliensis, N. pseudobrasiliensis, and N. wallacei, compared to linezolid MIC₅₀ values of 1, 2, 0.5, and 1 μg/ml, respectively. Tedizolid and linezolid MIC₉₀ values were 2 μg/ml for N. nova complex and N. brasiliensis Tedizolid MIC₅₀ and MIC₉₀ values for both N. cyriacigeorgica and N. farcinica were 0.5 μg/ml and 1 μg/ml, respectively, compared to linezolid MIC₅₀ and MIC₉₀ values of 2 and 4 μg/ml, respectively. Based on MIC₉₀ values, this study showed that tedizolid was 2- to 3-fold more active than linezolid in vitro against most common species of Nocardia, with the exception of the N. nova complex and N. brasiliensis, for which values were the same. These results may warrant evaluation of tedizolid as a potential treatment option for Nocardia infections.

In Vitro Susceptibility Testing of Tedizolid against Nontuberculous Mycobacteria

Tedizolid is a new oxazolidinone with improved in vitro and intracellular potency against Mycobacterium tuberculosis, including multidrug-resistant strains, and some species of nontuberculous mycobacteria (NTM) compared with that of linezolid. Using the current Clinical and Laboratory Standards Institute (CLSI)-recommended method of broth microdilution, susceptibility testing of 170 isolates of rapidly growing mycobacteria showed equivalent or lower (1- to 8-fold) MIC₅₀ and/or MIC₉₀ values for tedizolid compared with that for linezolid. The tedizolid MIC₉₀ values for 81 isolates of M. abscessus subsp. abscessus and 12 isolates of M. abscessus subsp. massiliense were 8 μg/ml and 4 μg/ml, respectively, compared with linezolid MIC₉₀ values of 32 μg/ml for both. The MIC₉₀ values for 20 isolates of M. fortuitum were 2 μg/ml for tedizolid and 4 μg/ml for linezolid. Twenty-two isolates of M. chelonae had tedizolid and linezolid MIC₉₀s of 2 μg/ml and 16 μg/ml, respectively. One hundred forty-two slowly growing NTM, including 7/7 M. marinum, 7/7 M. kansasii, and 7/11 of other less commonly isolated species, had tedizolid MICs of ≤1 μg/ml and linezolid MICs of ≤4 μg/ml. One hundred isolates of Mycobacterium avium complex and eight M. simiae isolates had tedizolid MIC₅₀s of 8 μg/ml and linezolid MIC₅₀s 32 and 64 μg/ml, respectively. Nine M. arupense isolates had MIC₅₀s of 4 μg/ml and 16 μg/ml for tedizolid and linezolid, respectively. These findings demonstrate a greater in vitro potency of tedizolid than linezolid against NTM and suggest that an evaluation of tedizolid as a potential treatment agent for infections caused by selected NTM is warranted.

Myelosuppression-sparing treatment of central nervous system nocardiosis in a multiple myeloma patient utilizing a tedizolid-based regimen: a case report

Central nervous system (CNS) nocardiosis is a recognised opportunistic infection in immunocompromised patients. Treatment involves prolonged institution of antibiotics, making oral agents a convenient and desired option. Unfortunately, devising an effective, well-tolerated antimicrobial for the duration required to treat CNS nocardiosis is challenging owing to treatment intolerance and toxicities. This report highlights myelosuppression-sparing treatment with an oral tedizolid-based regimen following a complicated course with standard agents. A 68-year-old female from Florida (USA) with low-risk lambda light chain multiple myeloma complicated by persistently low CD4 counts, absolute neutrophil counts and IgG levels presented 18 months after diagnosis with fever, pneumonia, new-onset atrial fibrillation, right-sided hemiparesis, encephalopathy and slurred speech. Magnetic resonance imaging (MRI) showed numerous ring-enhancing lesions, and blood cultures were positive for Nocardia farcinica. The patient failed initial therapy with trimethoprim/sulfamethoxazole (SXT), linezolid and imipenem plus surgical debridement of the frontal lobe abscess. Intraoperative cultures were positive for N. farcinica. The treatment course was also complicated by steadily declining white blood cell and platelet counts despite receiving filgrastim. She was therefore placed on SXT and tedizolid for 6 months. Subsequent brain MRI showed complete resolution of the lesions and thus chemotherapy for multiple myeloma was re-initiated. In conclusion, tedizolid-based regimens may be an option for patients with myelosuppression requiring prolonged antibiotic therapy for CNS nocardiosis.

In Vivo Activity of the Benzothiazinones PBTZ169 and BTZ043 against Nocardia brasiliensis

Background

Mycetoma is a neglected, chronic, and deforming infectious disease caused by fungi and actinomycetes. In Mexico, N. brasiliensis is the predominant etiologic agent. Therapeutic alternatives are necessary because the current drug regimens have several disadvantages. Benzothiazinones (BTZ) are a new class of candidate drugs that inhibit decaprenyl-phosphoribose-epimerase (DprE1), an essential enzyme involved in the cell wall biosynthesis of Corynebacterineae.

Methodology/Principal findings

In this study, the in vitro activity of the next generation BTZ, PBTZ169, was tested against thirty Nocardia brasiliensis isolates. The MIC₅₀ and MIC₉₀ values for PBTZ169 were 0.0075 and 0.03 μg/mL, respectively. Because Nocardia is a potential intracellular bacterium, a THP-1 macrophage monolayer was infected with N. brasiliensis HUJEG-1 and then treated with PBTZ169, resulting in a decrease in the number of colony-forming units (CFUs) at a concentration of 0.25X the in vitro value. The in vivo activity was evaluated after infecting female BALB/c mice in the right hind food-pad. After 6 weeks, treatment was initiated with PBTZ169 and its activity was compared with the first generation compound, BTZ043. Both BTZ compounds were administered at 100 mg/kg twice daily by gavage, and sulfamethoxazole/trimethoprim (SXT), at 100 mg/kg sulfamethoxazole, was used as a positive control. After 22 weeks of therapy, only PBTZ169 and SXT displayed statistically significant activity.

Conclusion

These results indicate that DprE1 inhibitors may be useful for treating infections of Nocardia and may therefore be active against other actinomycetoma agents. We must test combinations of these compounds with other antimicrobial agents, such as linezolid, tedizolid or SXT, that have good to excellent in vivo activity, as well as new DprE1 inhibitors that can achieve higher plasma levels.

Mycetoma is a neglected tropical disease caused by many etiological agents, including actinobacteria and true fungi. In Mexico, Nocardia brasiliensis and Actinomadura madurae account for more than 90% of the total cases. This subcutaneous infectious disease can affect skin and subcutaneous tissue; actinomycetomas are particularly osteolytic. The presence of abundant scar tissue, pus, and the intracellular growth of Nocardia make treatment very difficult. Current N. brasiliensis actinomycetoma therapy includes the use of trimethoprim-sulamethozaxole, diamino-diphenyl-sulphone (DDS), amikacin, and amoxicillin-clavulanate. N. brasiliensis is resistant to many other antimicrobials due in part to its richness in copies of genes related to pharmacoresistance, for instance rpoB, gyrase, beta-lactams, P450 cytochromes, etc. DprE1 inhibitors are new types of compounds that target a completely different gene, dprE1, encoding the decaprenylphosphoryl-d-ribose oxidase. Assays evaluating these experimental or other new drugs are necessary to develop a better therapeutic scheme for actinomycetoma, with more potent, less toxic antimicrobials.

Tedizolid for the management of human infections: in vitro characteristics

The emerging antibiotic resistance of Gram-positive pathogens represents a significant challenge to the management of human infections. The novel oxazolidinone tedizolid demonstrates antimicrobial activity across a broad range of Gram-positive pathogens and greater potency than linezolid against wild-type and drug-resistant pathogens, including linezolid-resistant Staphylococcus aureus strains possessing mutations in chromosomal genes encoding 23S rRNA or ribosomal proteins L3 or L4. Strains harboring such mutations are also selected for much less frequently with tedizolid than with linezolid. In addition, tedizolid has a significant potency advantage over linezolid-resistant strains carrying the horizontally transferable cfr gene. Methylation of A2503 of 23S rRNA by the Cfr methyltransferase confers resistance to linezolid (and a variety of other 50S ribosomal subunit-targeted antibiotics) but not to tedizolid because of structural differences in A-ring C5 substituents between the 2 drugs. The greater potency and improved resistance profile of tedizolid provides the microbiologic basis for considering this molecule as an alternative to linezolid for the treatment of serious infections caused by Gram-positive pathogens.

Potential role of tedizolid phosphate in the treatment of acute bacterial skin infections

Tedizolid phosphate (TR-701), a prodrug of tedizolid (TR-700), is a next-generation oxazolidinone that has shown favorable results in the treatment of acute bacterial skin and skin-structure infections in its first Phase III clinical trial. Tedizolid has high bioavailability, penetration, and tissue distribution when administered orally or intravenously. The activity of tedizolid was greater than linezolid against strains of Staphylococcus spp., Streptococcus spp., and Enterococcus spp. in vitro studies, including strains resistant to linezolid and those not susceptible to vancomycin or daptomycin. Its pharmacokinetic characteristics allow for a once-daily administration that leads to a more predictable efficacy and safety profile than those of linezolid. No hematological adverse effects have been reported associated with tedizolid when used at the therapeutic dose of 200 mg in Phase I, II, or III clinical trials of up to 3 weeks of tedizolid administration. Given that the clinical and microbiological efficacy are similar for the 200, 300, and 400 mg doses, the lowest effective dose of 200 mg once daily for 6 days was selected for Phase III studies in acute bacterial skin and skin-structure infections, providing a safe dosing regimen with low potential for development of myelosuppression. Unlike linezolid, tedizolid does not inhibit monoamine oxidase in vivo, therefore interactions with adrenergic, dopaminergic, and serotonergic drugs are not to be expected. In conclusion, tedizolid is a novel antibiotic with potent activity against Gram-positive microorganisms responsible for skin and soft tissue infections, including strains resistant to vancomycin, linezolid, and daptomycin, thus answers a growing therapeutic need.

Complete genome sequence of Nocardia brasiliensis HUJEG-1

In Mexico, actinomycetoma is mainly caused by Nocardia brasiliensis, which is a soil inhabitant actinobacterium. Here, we report for the first time the draft genome of a strain isolated from a human case that has largely been found in in vitro and experimental models of actinomycetoma, N. brasiliensis HUJEG-1.

Construction of a Nocardia brasiliensis fluorescent plasmid to study Actinomycetoma pathogenicity

Nocardia brasiliensis, is a bacteria that lives as saprophyte in soil and causes a disease called actinomycetoma in both human and animals. Nocardia brasiliensis is an intracellular, facultative bacterium that replicates and survives within host macrophages. The mechanisms involved in the evasion of the microbicidal actions of macrophages remain unclear. The filamentous growth of N. brasiliensis is resistant to unicellular preparations, leading to inaccurate quantification of bacterial numbers by means of colony forming units (CFU). As successful survival studies with green fluorescent protein (GFP)-expressing bacterial strains have been reported, we constructed a recombinant GFP-expressing strain of N. brasiliensis. The virulence of the modified strain is maintained because it induces mycetoma in BALB/c mice. This new strain can be used for bacterial survival assays using cytometry and to elucidate the pathogenicity mechanisms in Actinomycetoma infection.

In vitro activity of ACH-702, a new isothiazoloquinolone, against Nocardia brasiliensis compared with econazole and the carbapenems imipenem and meropenem alone or in combination with clavulanic acid

The in vitro activities of ACH-702 and other antimicrobials against 30 Nocardia brasiliensis isolates were tested. The MIC(50) (MIC for 50% of the strains tested) and MIC(90) values of ACH-702 were 0.125 and 0.5 microg/ml. The same values for econazole were 2 and 4 microg/ml. The MIC(50) and MIC(90) values of imipenem and meropenem were 64 and >64 microg/ml and 2 and 8 microg/ml, respectively; the addition of clavulanic acid to the carbapenems had no effect.