In vitro evaluation of AZD2563, a new oxazolidinone, tested against unusual gram-positive species

The in vitro antimicrobial activity of linezolid against unconventional pathogens

Linezolid is an oxazolidinone antibiotic that is mainly permitted to treat Gram-positive bacterial infections. Recent studies have shown that linezolid also has antibacterial effects on several other bacteria outside the package insert, including Mycobacterium tuberculosis, non-tuberculous mycobacteria (NTM), Nocardia, Corynebacterium, and anaerobes, etc. Interestingly, linezolid also has an in vitro inhibitory effect on fungi. This review focuses on the in vitro antibacterial activity of linezolid against microorganisms outside its antibacterial spectrum. We mainly listed the number of the tested strains, the minimum inhibitory concentration (MIC) range, MIC50, and MIC90 of linezolid against those pathogens outside the package insert. The results showed that among these tested pathogens, linezolid displayed strong inhibitory effects against M. tuberculosis, Nocardia, and Corynebacterium, with an MIC range of ≤2 μg/mL. As for NTM, linezolid exhibited moderate to potent inhibitory effects against the strains of different species with an MIC range of 0.06-128 μg/mL. Moreover, linezolid was reported to have a species-dependent inhibitory effect on anaerobes at a concentration range of 0.003-16 μg/mL. Furthermore, linezolid could enhance azoles and amphotericin B's antifungal activity on Candida synergistically. It is hoped that this analysis can provide data for expanding the application of linezolid, make the off-label drug use have more compelling evidence, and provide clues for the development of new drugs.

The crucial role of catheters in micrococcal bloodstream infections in cancer patients

Micrococcus bacteria are frequently isolated from blood cultures and could represent a cause of infections associated with medical devices, particularly in immunocompromised patients; however, there is a lack of information on the management of micrococcal bacteremia. We report what is, to our knowledge, the largest series of cases of micrococcal bacteremia ever studied and the great impact of catheter removal on its outcome.

Minimal inhibitory concentrations of linezolid against clinical isolates of coryneform bacteria

In order to evaluate the efficacy of linezolid for treating severe infections with coryneform bacteria, the activity of linezolid was tested in vitro against 425 clinically relevant isolates of coryneform bacteria and compared with the activity of penicillin and erythromycin. The minimal inhibitory concentration of linezolid did not exceed 2 microg/ml for any of the isolates tested, indicating that this agent has very good activity against coryneform bacteria. These results suggest linezolid is a possible alternative antimicrobial agent for the treatment of severe infections caused by coryneform bacteria.

Listeria monocytogenes infection in patients with cancer

Listeriosis (LT) is an important infection in immunocompromised patients, but no large series of LT in cancer patients have been recently described. We reviewed the records of 34 cancer patients with LT at our institution (1990-2001). Twenty patients (59%) had an underlying hematologic malignancy. In 11 patients, LT complicated bone marrow transplantation. Lymphocytopenia was observed in 62% of the patients. Twenty-six patients (76%) received prior corticosteroids. Bacteremia was the most common presentation of LT (74%) followed by meningoencephalitis (21%). The most common treatment of LT was ampicillin with or without gentamicin (68%). The median duration of treatment was 26 days (range, 8-74 days). The rate of response to antimicrobial therapy was 79%. No relapses were identified. LT contributed to death in 9 (75%) of the 12 patients who died. Meningoencephalitis had the worst prognosis (3 of 6 cases were fatal). Treatment of central nervous system LT continues to have a high failure rate.

Synthesis and antibacterial activity of oxazolidinone containing sulphonyl group

A series of oxazolidinone derivatives carrying sulphonyl group was synthesized and their antibacterial activity was evaluated in vitro. Many of such compounds demonstrated potent antibacterial activity. The activity of a novel compound (YC-20) was 2-4-fold more potent than that of linezolid.

Novel agents for the treatment of resistant Gram-positive infections

Bacteria have proved themselves able to develop resistance to every antibiotic used clinically. Traditional agents used for treatment of serious infections caused by Gram-positive species have recently been supplemented with the introduction of linezolid, quinupristin-dalfopristin, several new quinolones and telithromycin. However, resistance to many of these agents has already been reported and, although each currently retains activity against the vast majority of clinical isolates of its target species, their long-term efficacy is uncertain. We must look to develop other compounds to replace and hopefully improve upon existing anti-Gram-positive agents. Daptomycin (a lipopeptide), oritavancin and dalbavancin (both second-generation glycopeptides) and ramoplanin (a glycolipodepsipeptide) are among the agents in advanced stages of development and, at present, many seem likely to proceed to licensing. In addition, it is encouraging that many agents active against novel bacterial targets have been discovered and are in earlier stages of development. In the next two decades, we should be optimistic that a regular flow of new anti-Gram-positive agents will enable us to offset the constant spectre of bacterial resistance.

Determination of disk diffusion and MIC quality control parameters for AZD2563, a novel long-acting oxazolidinone

AZD2563 is a new, long-acting oxazolidinone that possesses potent antimicrobial activity against Gram-positive organisms. This report summarizes the results of broth microdilution MIC and disk diffusion quality control (QC) investigations for AZD2563. All tests or methods (M2-A7 and M7-A5) and QC study designs (M23-A2) were those published by the National Committee for Clinical Laboratory Standards. QC strains tested against AZD2563 included: Staphylococcus aureus ATCC 25923 and ATCC 29213, Enterococcus faecalis ATCC 29212 and Streptococcus pneumoniae ATCC 49619. In the eight-center QC trial, 320 and 480 results were generated for MIC and disk diffusion tests, respectively. The selected 7-mm ranges for the two disk diffusion QC organisms contained > or = 98.5% of reported results. Proposed 3 or 4 log(2) dilution MIC ranges contained all reported participant results. AZD2563 disk diffusion zone diameters were generally 2-3 mm smaller than the corresponding linezolid zone diameters. In conclusion, QC ranges for AZD2563 MIC and disk diffusion methods were established and appear acceptable in preparation for the clinical trials use.

Detection of oxazolidinone-resistant Enterococcus faecalis and Enterococcus faecium strains by real-time PCR and PCR-restriction fragment length polymorphism analysis

A real-time PCR assay identified linezolid-resistant Enterococcus faecalis and Enterococcus faecium isolates with a G2576U rRNA mutation. PCR-restriction fragment length polymorphism analysis of ribosomal DNA amplicons with NheI also detected this mutation. Both assays detected isolates heterozygous at this position. Recognition of isolates with what is presently the most frequent oxazolidinone resistance mutation may aid surveillance and individual case management.