Little difference between minimum inhibitory concentrations of Mycobacterium tuberculosis wild-type organisms determined with BACTEC MGIT 960 and Middlebrook 7H10.

The MIC wild-type (WT) distribution for Mycobacterium tuberculosis in BACTEC 960 MGIT is not defined, which may result in poor reproducibility for drug susceptibility testing (DST), as several DST methods with different breakpoints are in use. In a comparison between MGIT and Middlebrook 7H10 medium of seven first- and second-line drugs, including 133 MIC determinations of 15 WT isolates, we found an agreement of 91.7% within ± one MIC dilution step. The results confirm the agreement in MIC testing between 7H10 and MGIT and indicate that breakpoints could be harmonized in order to avoid misclassification.

Wild-type distributions of seven oral second-line drugs against Mycobacterium tuberculosis.

OBJECTIVES: To determine wild-type minimum inhibitory concentration (MIC) distributions for Mycobacterium tuberculosis, as the background data for defining susceptibility breakpoints are limited. METHODS: We determined wild-type MIC distributions of M. tuberculosis using a 96-stick replicator in Middlebrook 7H10 (7H10) medium for ethionamide (ETH), prothionamide, thiacetazone, cycloserine, rifabutin (RFB), clofazimine and linezolid in consecutive susceptible clinical isolates (n = 78). RESULTS: Tentative epidemiological wild-type cut-offs (ECOFF) were determined for all investigated drugs where World Health Organization recommended critical concentrations for 7H10 are lacking, except for ETH. As the ECOFF was closely related to the non-wild-type strains for ETH and thiacetazone, the use of an intermediary (I) category in drug susceptibility testing could increase reproducibility. The cross-resistance between ETH and isoniazid was 21%. Applying 0.5 mg/l as a breakpoint for RFB classified two non-wild type and rpoB mutated isolates as susceptible for RFB and resistant against rifampicin. CONCLUSIONS: We propose that wild-type MIC distributions should be used as a tool to define clinical breakpoints against second-line drugs. This is increasingly important considering the rapid emergence of drug resistance.

Wild-type MIC distributions of four fluoroquinolones active against Mycobacterium tuberculosis in relation to current critical concentrations and available pharmacokinetic and pharmacodynamic data.

OBJECTIVES: To describe wild-type distributions of the MIC of fluoroquinolones for Mycobacterium tuberculosis in relation to current critical concentrations used for drug susceptibility testing and pharmacokinetic/pharmacodynamic (PK/PD) data. METHODS: A 96-stick replicator on Middlebrook 7H10 medium was used to define the MICs of ciprofloxacin, ofloxacin, moxifloxacin and levofloxacin for 90 consecutive clinical strains and 24 drug-resistant strains. The MICs were compared with routine BACTEC 460 susceptibility results and with MIC determinations in the BACTEC MGIT 960 system in a subset of strains using ofloxacin as a class representative. PK/PD data for each drug were reviewed in relation to the wild-type MIC distribution. RESULTS: The wild-type MICs of ciprofloxacin, ofloxacin, moxifloxacin and levofloxacin were distributed from 0.125 to 1, 0.25 to 1, 0.032 to 0.5 and 0.125 to 0.5 mg/L, respectively. The MIC data correlated well with the BACTEC 960 MGIT and BACTEC 460 results. PD indices were the most favourable for levofloxacin, followed by moxifloxacin, ofloxacin and ciprofloxacin. CONCLUSIONS: We propose S (susceptible)

Drug susceptibility testing of Mycobacterium tuberculosis by a nitrate reductase assay applied directly on microscopy-positive sputum samples.

Current methods for drug susceptibility testing of Mycobacterium tuberculosis are either costly or slow. As the prevalence of multidrug-resistant strains increases, the need for fast, reliable, and inexpensive methods that can also be applied in settings with scarce resources is obvious. We evaluated a rapid colorimetric nitrate reductase assay (NRA) for direct drug susceptibility testing of M. tuberculosis directly from clinical sputum samples with positive microscopy results for acid-fast bacilli with more than 10 acid-fast bacilli per high-power field. We have saved valuable time by omitting the preisolation step. The sensitivity (ability to detect true drug resistance) and specificity (ability to detect true drug susceptibility) of the direct NRA, using the direct proportion method as the reference, were 100 and 100%, 93 and 100%, 76 and 100%, and 55 and 99% for rifampin, isoniazid, streptomycin, and ethambutol, respectively, when tested on M. tuberculosis strains present in 121 samples. The results were in most cases available in 14 days. The direct NRA could be used as a rapid, inexpensive, and accurate method to determine rifampin and isoniazid susceptibility directly from sputum. The technique might become a valid alternative to traditional methods, especially in low-income countries.

Should the 'bleach microscopy method' be recommended for improved case detection of tuberculosis? Literature review and key person analysis.

SETTING: It has been proposed that the sensitivity of direct sputum smear microscopy can be improved if sputum is liquefied with sodium hypochlorite (NaOCl or household bleach), and concentrated by centrifugation before acid-fast staining. OBJECTIVE: To summarise the results of the studies of the bleach method for improved sensitivity of sputum microscopy and to describe the opinions and knowledge of key persons in National Tuberculosis Control Programmes (NTPs) about this method. DESIGN: We searched Medline, EMBASE and Web of Science for studies comparing the bleach method to direct sputum smear microscopy in low- or middle-income countries. Each study was assessed regarding methodology and field applicability. We also sent out questionnaires concerning the bleach method to key persons in NTPs in 85 countries. RESULTS: In 15 of the 19 studies identified there was a statistically significant improvement in the proportion of positive tests or sensitivity ranging from 7-253%. The majority (73%) of the key persons had heard of the bleach method. Forty-four per cent thought it could improve case detection in their countries, while 49% did not know; 93% of them would promote the bleach method; the most common reasons for doing so would be recommendations from the WHO or the IUATLD, or favourable studies performed in their own country. The bleach method was used routinely in only three countries. CONCLUSION: There is enough evidence to recommend the evaluation and introduction of the bleach method in most settings where mycobacterial culture is not performed routinely.

Evaluation of the BacT/ALERT 3D system for recovery and drug susceptibility testing of Mycobacterium tuberculosis.

We evaluated the BacT/ALERT 3D system for recovery and drug susceptibility testing (DST) of Mycobacterium tuberculosis (MTB). Of 2659 clinical specimens, MTB was detected in 92 using BacT/ALERT, compared to 94 using Löwenstein-Jensen culture. Detection time was 25% shorter with BacT/ALERT. Sensitivities were 92%, 96%, 78% and 100% for resistance to rifampicin, isoniazid, streptomycin and ethambutol, respectively, while specificity was 100% for all antibiotics, when BacT/ALERT was compared with the BACTEC 460 method on 50 MTB isolates. The BacT/ALERT system is fully automated and creates no radioactive waste. It seems to be a valid alternative for primary isolation, but further evaluation is needed regarding DST.

Rapid and inexpensive drug susceptibility testing of Mycobacterium tuberculosis with a nitrate reductase assay.

Multidrug-resistant tuberculosis is an increasing public health concern in many parts of the world, especially in low-income countries, where most cases occur. Traditional drug susceptibility testing is either time-consuming, such as the proportion method on solid media, or expensive, such as the BACTEC 460 system. We have evaluated a new nitrate reductase assay (NRA) that depends on the ability of Mycobacterium tuberculosis to reduce nitrate to nitrite. The reduction can be detected using specific reagents, which produce a color change. We tested a panel of 57 M. tuberculosis strains with various resistance patterns. The bacteria were inoculated on Löwenstein-Jensen medium, either without drugs or with rifampin, isoniazid, streptomycin, or ethambutol and with potassium nitrate (KNO(3)) incorporated. After incubation for 7, 10, or 14 days, the reagents were added and nitrate reduction, indicating growth, could be detected by a color change. Sensitivities to and specificities for drugs as determined by the NRA method compared to those determined by the BACTEC 460 method were 100 and 100% for rifampin, 97 and 96% for isoniazid, 95 and 83% for streptomycin, and 75 and 98% for ethambutol, respectively. The results were in the majority of the cases available in 7 days. The evaluated method is rapid and inexpensive and could correctly identify most resistant and sensitive M. tuberculosis strains. It has the potential to become an interesting alternative to existing methods, such as the proportion and BACTEC methods, particularly in resource-poor settings.

Improved sputum microscopy for a more sensitive diagnosis of pulmonary tuberculosis.

Diagnosis of tuberculosis in low-income countries is hindered by the low sensitivity of direct sputum smear microscopy. We compared an improved method based on liquefaction of sputum with NaOCl followed by centrifugation with standard direct smear in a central hospital and at peripheral health centres in Honduras. Specificity was high and sensitivity significantly better with the NaOCl method. Moreover, this technique is safe, inexpensive and easy to perform. We recommend its implementation to enable rapid, sensitive laboratory diagnosis of pulmonary tuberculosis, especially in resource-poor settings where culture is not possible.