Akos Somoskovi

Erm(41)-dependent inducible resistance to azithromycin and clarithromycin in clinical isolates of Mycobacterium abscessus

OBJECTIVESnThe ribosomal methylase Erm(41) confers inducible resistance to macrolides in Mycobacterium abscessus. The aim of this work was to systematically study and compare drug susceptibility to clarithromycin and azithromycin in M. abscessus and Mycobacterium chelonae clinical isolates with a particular focus on inducible drug resistance.nnnMETHODSnClinical isolates of M. abscessus subsp. abscessus (nu200a=u200a21), M. abscessus subsp. bolletii (nu200a=u200a16), M. abscessus subsp. massiliense (nu200a=u200a10) and M. chelonae (nu200a=u200a22) were characterized regarding their erm(41) and rrl genotypes and subjected to drug susceptibility testing (DST) for clarithromycin and azithromycin. Microdilution DST was performed in cation-adjusted Mueller-Hinton broth (pH 7.4) with readings at days 3, 7 and 12 and with pre-incubation at subinhibitory macrolide concentrations for erm(41) induction. In addition, the influence of variations in pH and growth medium on DST results was examined.nnnRESULTSnMICs of azithromycin were consistently higher than those of clarithromycin. In strains with an inducible erm(41) gene, high median MICs of ≥256 mg/L on day 12 were observed for both clarithromycin and azithromycin. Inducible resistance was at least as pronounced for azithromycin as for clarithromycin.nnnCONCLUSIONSnOur findings do not support the suggestion of a preferential use of azithromycin over clarithromycin in order to limit inducible macrolide resistance. Both compounds provoked a comparable resistance phenotype in M. abscessus. Caution is needed when using either azithromycin or clarithromycin for treatment of M. abscessus infections.

A mutation associated with clofazimine and bedaquiline cross-resistance in MDR-TB following bedaquiline treatment

The world-wide increase in the incidence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) poses a major clinical challenge. The treatment outcome of MDR-TB and XDR-TB patients is often poor and unsuccessful in the absence of an optimal number of active drugs [1]. Novel antituberculous compounds are urgently required and only very few, such as bedaquiline, have recently been approved for tuberculosis treatment [2]. In a recent phase 2b clinical trial that was based on a 160 newly diagnosed MDR-TB patients, the addition of bedaquiline to a preferred background regimen for 24 weeks resulted in faster culture conversion and significantly more culture conversion at 120 weeks compared with the control group. However, there were more deaths in the bedaquiline than in the placebo group and half of these patients died due to tuberculosis. So far, it is unclear whether the death of any of these patients may have been associated with diminished susceptibility to bedaquiline [3]. Acquired clofazimine and bedaquiline cross-resistance in a patient due to mutation in the M. tuberculosis Rv0678 gene http://ow.ly/Cnkk7

Diagnostic Implications of Inconsistent Results Obtained with the Xpert MTB/Rif Assay in Detection of Mycobacterium tuberculosis Isolates with an rpoB Mutation Associated with Low-Level Rifampin Resistance

ABSTRACT Xpert-MTB/Rif is one of the most frequently used molecular screening tests for multidrug-resistant tuberculosis worldwide. We report false-negative assay results in the presence of rpoB Leu533Pro, which is associated with low-level phenotypic rifampin resistance. Accurate and timely confirmation of rifampin susceptibility results obtained with Xpert-MTB/Rif is imperative.

Drug susceptibility distributions in slowly growing non-tuberculous mycobacteria using MGIT 960 TB eXiST

In general, uniform clinical antibiotic susceptibility breakpoints (CBPs) for slowly growing nontuberculous mycobacteria (NTM) have not been established. The aim of this study was to determine wild-type drug susceptibility distributions for relevant antibiotics using Bactec MGIT 960 equipped with EpiCenter TB eXiST and to derive epidemiological cut-offs (ECOFFs) from semi quantitative drug susceptibility measurements. One hundred and twenty-six NTM clinical isolates (Mycobacterium avium n=58, Mycobacterium intracellulare n=18, Mycobacterium kansasii n=50) were investigated in this study. Drug susceptibility distributions and MIC90 values were determined for clarithromycin, ethambutol, rifampicin, rifabutin, ofloxacin, moxifloxacin, and amikacin using Bactec MGIT 960/EpiCenter TB eXiST. For most species/drug combinations ECOFFs were determined. For some species/drug combinations ECOFFs were not defined as either the isolates were susceptible to the lowest drug concentration tested or because isolates, in part, had MIC levels exceeding the highest drug concentration tested. This study describes drug susceptibility distributions and MIC90 values of M. avium, M. intracellulare, and M. kansasii that may aid the definition of CBPs when correlating in vitro drug susceptibility with clinical outcomes in future studies.

Integrating the Xpert MTB/RIF Assay into a Diagnostic Workflow for Rapid Detection of Mycobacterium tuberculosis in a Low-Prevalence Area

ABSTRACT The Xpert MTB/RIF assay is a rapid and fully automated real-time PCR assay. The performance of the Xpert MTB/RIF assay as a primary screening test for urgent clinical specimens was evaluated during a 2-year period. The results showed that replacing smear microscopy with the Xpert MTB/RIF assay facilitates laboratory handling and improves the sensitivity and specificity of Mycobacterium tuberculosis detection.

Transmission of multidrug-resistant tuberculosis in a low-incidence setting, Switzerland, 2006 to 2012

The goal of the present study was to examine the transmission dynamics of multidrug-resistant tuberculosis (MDR-TB) in Switzerland. Between 2006 and 2012, a total of 49 MDR-TB cases were reported to the Swiss Federal Office of Public Health, 46 of which were of foreign origin. All 49 initial strains were evaluated by molecular epidemiologic methods at the Swiss National Reference Centre for Mycobacteria. In 43 strains, unique DNA fingerprint patterns were identified. Twelve strains were grouped into six clusters. Data from contact tracing suggest likely in-country transmission in four clusters, mostly among close contacts. In the remaining two clusters, no contact tracing data were available, but the identified genotypes were known to be prevalent in the countries of origin of the patients, suggesting the possibility that the infection was acquired there. While most MDR-TB cases are imported to Switzerland, at least four of the 49 MDR-TB cases were due to transmission within the country. The imported cases, however, did not lead to secondary cases outside the circles of close contacts. The results also indicate that prevention of MDR-TB transmission among immigrants may require closer monitoring.

Novel laboratory diagnostic tests for tuberculosis and their potential role in an integrated and tiered laboratory network

Lack of laboratory capacity in high-burden countries presents a significant barrier in providing diagnosis and treatment to patients infected with HIV/AIDS, tuberculosis (TB), and malaria. Strengthening laboratory services in these settings via implementation of novel diagnostic tests is especially indispensable to battle against TB and MDR/XDR-TB. Novel TB diagnostic assays have to be applicable to field conditions, affordable and accessible to all patients at different levels of the tiered laboratory network. A functional laboratory network should be based on well-developed diagnostic platforms that can provide not only timely and adequate diagnosis but are simple to use, and easy to implement and sustain. The article is overviewing the latest developments of TB laboratory diagnostics such as smear microscopy, rapid growth detection and susceptibility testing and rapid molecular testing with focus on performance and applicability to diagnostic needs at different levels of the diagnostic network.