Nitrate reductase assay using sodium nitrate for rapid detection of multidrug resistant tuberculosis

We validated the nitrate reductase assay (NRA) for the detection of multidrug-resistant Mycobacterium tuberculosis (MDR-TB) using sodium nitrate (NaNO3) in replacement of potassium nitrate (KNO3) as nitrate source. NaNO3 is cheaper than KNO3 and has no restriction on use which facilitates the implementation of NRA to detect MDR-TB.

Nitrate reductase assay using sodium nitrate for rapid detection of multidrug resistant tuberculosis.

We validated the nitrate reductase assay (NRA) for the detection of multidrug-resistant Mycobacterium tuberculosis (MDR-TB) using sodium nitrate (NaNO3) in replacement of potassium nitrate (KNO3) as nitrate source. NaNO3 is cheaper than KNO3 and has no restriction on use which facilitates the implementation of NRA to detect MDR-TB.

Multicentre laboratory validation of the colorimetric redox indicator (CRI) assay for the rapid detection of extensively drug-resistant (XDR) Mycobacterium tuberculosis.

OBJECTIVES: To perform a multicentre study to evaluate the performance of the colorimetric redox indicator (CRI) assay and to establish the MICs and critical concentrations of rifampicin, isoniazid, ofloxacin, kanamycin and capreomycin. METHODS: The study was carried out in two phases. Phase I determined the MIC of each drug. Phase II established critical concentrations for the five drugs tested by the CRI assay compared with the conventional proportion method. RESULTS: Phase I: a strain was considered resistant by the CRI assay if the MIC was ≥0.5 mg/L for rifampicin, ≥0.25 mg/L for isoniazid, ≥4.0 mg/L for ofloxacin and ≥5.0 mg/L for kanamycin and capreomycin. Sensitivity was 99.1% for isoniazid and 100% for the other drugs and specificity was 97.9% for capreomycin and 100% for the other drugs. Phase II: the critical concentration was 0.5 mg/L for rifampicin, 0.25 mg/L for isoniazid, 2.0 mg/L for ofloxacin and 2.5 mg/L for kanamycin and capreomycin giving an overall accuracy of 98.4%, 96.6%, 96.7%, 98.3% and 90%, respectively. CONCLUSIONS: Results demonstrate that the CRI assay is an accurate method for the rapid detection of XDR Mycobacterium tuberculosis. The CRI assay is faster than the conventional drug susceptibility testing method using solid medium, has the same turnaround time as the BACTEC MGIT 960 system, but is less expensive, and could be an adequate method for low-income countries.

Evaluation of the BD MGIT TBc Identification Test (TBc ID), a rapid chromatographic immunoassay for the detection of Mycobacterium tuberculosis complex from liquid culture.

The BACTEC MGIT 960 system is increasingly used to culture Mycobacterium tuberculosis. We evaluated the performance of the new immunochromatographic assay BD MGIT TBc Identification Test (TBc ID) for the rapid identification of M. tuberculosis complex in clinical samples when performed directly from BACTEC MGIT 960 culture positive for acid-fast bacilli (AFB). Of 92 cultures evaluated, the sensitivity and specificity of the TBc ID test was 98.5% and 100%, respectively compared to sequencing of the 16S rRNA gene. One culture that was TBc ID test negative but that was identified as M. tuberculosis by 16S rRNA sequencing was confirmed to have a mutation in the mpt64 gene. The TBc ID test is an easy and sensitive method for the identification of M. tuberculosis complex in liquid culture medium, does not require a high level of skills, neither any additional specific equipment and gives results in 15 min, which provide a good alternative for the rapid identification of M. tuberculosis complex in liquid medium.

Low Occurrence of Tuberculosis Drug Resistance among Pulmonary Tuberculosis Patients from an Urban Setting, with a Long-Running DOTS Program in Zambia.

We set out to determine the levels of Mycobacterium tuberculosis resistance to first- and second-line TB drugs in an urban population in Zambia. Sputum samples were collected consecutively from all smear-positive, new and previously treated patients, from four diagnostic centres in Ndola between January and July 2006. Drug susceptibility testing was performed using the proportion method against four first- and two second-line TB drugs. Results. Among 156 new cases, any resistance was observed to be 7.7%, monoresistance to isoniazid and rifampicin was 4.5% and 1.3%, respectively. Of 31 retreatment cases, any resistance was observed to be 16.1%, monoresistance to isoniazid and rifampicin was 3.3% for each drug, and one case of resistance to both isoniazid and rifampicin (multidrug resistance) was detected. No resistance to kanamycin or ofloxacin was detected. Conclusion. Although not representative of the country, these results show low levels of drug resistance in a community with a long-standing DOTS experience. Resource constrained countries may reduce TB drug resistance by implementing community-based strategies that enhance treatment completion.

High level of cross-resistance between kanamycin, amikacin, and capreomycin among Mycobacterium tuberculosis isolates from Georgia and a close relation with mutations in the rrs gene.

The aminoglycosides kanamycin and amikacin and the macrocyclic peptide capreomycin are key drugs for the treatment of multidrug-resistant tuberculosis (MDR-TB). The increasing rates of resistance to these drugs and the possible cross-resistance between them are concerns for MDR-TB therapy. Mutations in the 16S rRNA gene (rrs) have been associated with resistance to each of the drugs, and mutations of the tlyA gene, which encodes a putative rRNA methyltransferase, are thought to confer capreomycin resistance in Mycobacterium tuberculosis bacteria. Studies of possible cross-resistance have shown variable results. In this study, the MICs of these drugs for 145 clinical isolates from Georgia and the sequences of the rrs and tlyA genes of the isolates were determined. Of 78 kanamycin-resistant strains, 9 (11.5%) were susceptible to amikacin and 16 (20.5%) were susceptible to capreomycin. Four strains were resistant to capreomycin but were susceptible to the other drugs, whereas all amikacin-resistant isolates were resistant to kanamycin. Sequencing revealed six types of mutations in the rrs gene (A514C, C517T, A1401G, C1402T, C1443G, T1521C) but no mutations in the tlyA gene. The A514C, C517T, C1443G, and T1521C mutations showed no association with resistance to any of the drugs. The A1401G and C1402T mutations were observed in 65 kanamycin-resistant isolates and the 4 capreomycin-resistant isolates, respectively, whereas none of the susceptible isolates showed either of those mutations. The four mutants with the C1402T mutations showed high levels of resistance to capreomycin but no resistance to kanamycin and amikacin. Detection of the A1401G mutation appeared to be 100% specific for the detection of resistance to kanamycin and amikacin, while the sensitivities reached 85.9% and 94.2%, respectively.

Thin layer agar compared to BACTEC MGIT 960 for early detection of Mycobacterium tuberculosis.

We compared the sensitivity and time to detection of growth of Mycobacterium tuberculosis in the thin layer agar (TLA) compared to BACTEC MGIT960. The average time for growth of M. tuberculosis in TLA and BACTEC MGIT960 was 10.6 and 9.6 days, respectively. The sensitivity of detection of M. tuberculosis was 97.3% on TLA and 97% on BACTEC MGIT960 for smear positive samples. TLA showed comparable results to BACTEC MGIT960 and could be an alternative method for low-income countries.

Fine-needle aspiration, an efficient sampling technique for bacteriological diagnosis of nonulcerative Buruli ulcer.

Invasive punch or incisional skin biopsy specimens are currently employed for the bacteriological confirmation of the clinical diagnosis of Buruli ulcer (BU), a cutaneous infectious disease caused by Mycobacterium ulcerans. The efficacy of fine-needle aspirates (FNA) using fine-gauge needles (23G by 25 mm) for the laboratory confirmation of BU was compared with that of skin tissue fragments obtained in parallel by excision or punch biopsy. In three BU treatment centers in Benin, both types of diagnostic material were obtained from 33 clinically suspected cases of BU and subjected to the same laboratory analyses: i.e., direct smear examination, IS2404 PCR, and in vitro culture. Twenty-three patients, demonstrating 17 ulcerative and 6 nonulcerative lesions, were positive by at least two tests and were therefore confirmed to have active BU. A total of 68 aspirates and 68 parallel tissue specimens were available from these confirmed patients. When comparing the sensitivities of the three confirmation tests between FNA and tissue specimens, the latter yielded more positive results, but only for PCR was this significant. When only nonulcerative BU lesions were considered, however, the sensitivities of the confirmation tests using FNA and tissue specimens were not significantly different. Our results show that the minimally invasive FNA technique offers enough sensitivity to be used for the diagnosis of BU in nonulcerative lesions.

Rapid detection of Mycobacterium tuberculosis resistance to second-line drugs by use of the manual mycobacterium growth indicator tube system.

The objective of this study was to evaluate the manual mycobacterium growth indicator tube (MGIT) system for the testing of Mycobacterium tuberculosis susceptibility to second-line drugs compared to the proportion method. One hundred eighty-eight M. tuberculosis isolates were tested for susceptibility to ofloxacin, kanamycin, ethionamide, and capreomycin by the manual MGIT, and results were compared to those obtained with the proportion method on 7H11 agar, considered a reference method. Results for ofloxacin and capreomycin were excellent, with 100% accuracy, and a result of 99.4% accuracy was achieved for kanamycin. For ethionamide, accuracy was lower, with a result of 86.7% compared to that of the proportion method. We proposed the following critical concentrations for the drugs: for ofloxacin, 2.0 microg/ml; for kanamycin, 2.5 microg/ml; for ethionamide, 5 microg/ml; and for capreomycin, 2.5 microg/ml. The time required to obtain results was an average of 8 days by the manual MGIT and 3 weeks by the reference method. Our results show that the manual MGIT is an accurate method for the rapid susceptibility testing of M. tuberculosis to second-line drugs. There is no need for a machine when using the manual MGIT, and results can be read with a simple UV lamp or with a semiquantitative reader, which considerably reduces the cost of the method.

First cultivation and characterization of Mycobacterium ulcerans from the environment.

BACKGROUND: Mycobacterium ulcerans disease, or Buruli ulcer (BU), is an indolent, necrotizing infection of skin, subcutaneous tissue and, occasionally, bones. It is the third most common human mycobacteriosis worldwide, after tuberculosis and leprosy. There is evidence that M. ulcerans is an environmental pathogen transmitted to humans from aquatic niches; however, well-characterized pure cultures of M. ulcerans from the environment have never been reported. Here we present details of the isolation and characterization of an M. ulcerans strain (00-1441) obtained from an aquatic Hemiptera (common name Water Strider, Gerris sp.) from Benin. METHODOLOGY/PRINCIPAL FINDINGS: One culture from a homogenate of a Gerris sp. in BACTEC became positive for IS2404, an insertion sequence with more than 200 copies in M. ulcerans. A pure culture of M. ulcerans 00-1441 was obtained on Löwenstein-Jensen medium after inoculation of BACTEC culture in mouse footpads followed by two other mouse footpad passages. The phenotypic characteristics of 00-1441 were identical to those of African M. ulcerans, including production of mycolactone A/B. The nucleotide sequence of the 5' end of 16S rRNA gene of 00-1441 was 100% identical to M. ulcerans and M. marinum, and the sequence of the 3' end was identical to that of the African type except for a single nucleotide substitution at position 1317. This mutation in M. ulcerans was recently discovered in BU patients living in the same geographic area. Various genotyping methods confirmed that strain 00-1441 has a profile identical to that of the predominant African type. Strain 00-1441 produced severe progressive infection and disease in mouse footpads with involvement of bone. CONCLUSION: Strain 00-1441 represents the first genetically and phenotypically identified strain of M. ulcerans isolated in pure culture from the environment. This isolation supports the concept that the agent of BU is a human pathogen with an environmental niche.

Primary culture of Mycobacterium ulcerans from human tissue specimens after storage in semisolid transport medium.

Tissue specimens collected from patients with clinically suspected Buruli ulcer treated in two Buruli ulcer treatment centers in Benin between 1998 and 2004 were placed in semisolid transport medium and transported at ambient temperature for microbiological analysis at the Institute of Tropical Medicine in Antwerp, Belgium. The impact of the delay before microbiological analysis on primary culture of Mycobacterium ulcerans was investigated. The length of storage in semisolid transport medium varied from 6 days to 26 weeks. Of the 1,273 tissue fragments positive for M. ulcerans DNA by an IS2404-specific PCR, 576 (45.2%) yielded positive culture results. The sensitivity of direct smear examination was 64.6% (822/1,273 tissue fragments). The median time required to obtain a positive culture result was 11 weeks. Positive cultures were obtained even from samples kept for more than 2 months at ambient temperatures. Moreover, there was no reduction in the viability of M. ulcerans, as detected by culture, when specimens remained in semisolid transport medium for long periods of time (up to 26 weeks). We can conclude that the method with semisolid transport medium is very robust for clinical specimens from patients with Buruli ulcer that, due to circumstances, cannot be analyzed in a timely manner. This transport medium is thus very useful for the confirmation of a diagnosis of Buruli ulcer with specimens collected in the field.

Application of the hsp65 PRA method for the rapid identification of mycobacteria isolated from clinical samples in Belgium.

Biochemical identification of mycobacteria is slow and many times fail to produce correct results. We compared PCR-restriction fragment length polymorphism analysis (PRA) of hsp65 and biochemical methods for the identification of mycobacteria from human samples in Belgium. PRA was found useful in the identification of mycobacteria and simple to implement as a quick method in the laboratory.

Endogenous reactivation and true treatment failure as causes of recurrent tuberculosis in a high incidence setting with a low HIV infection.

OBJECTIVE: To determine the relative frequencies of reinfection vs. reactivation or treatment failure in patients from a high tuberculosis incidence setting with a low prevalence of HIV infection. METHOD: We performed DNA fingerprinting on serial isolates from one and multiple TB episodes from 97 retreatment patients; 35 patients had been previously cured, whereas 62 had not. RESULTS: DNA fingerprinting patterns of recurrence Mycobacterium tuberculosis isolates of 5 of the 35 previously cured patients did not match with those of the corresponding initial isolates, indicating reinfection. We did not document reinfection during treatment. Isolates from each of the remaining 30 previously cured patients had identical DNA fingerprinting results, indicating reactivation. DNA fingerprinting patterns of isolates from the 62 patients with persistently positive sputum smears were identical, suggesting treatment failure. CONCLUSION: These findings suggest that reinfection is not a common cause of relapse and treatment failure in this rural predominantly HIV-free population despite the high incidence of TB.

Preliminary observations on Mycobacterium spp. in dairy cattle in Ecuador.

This study evaluated bovine tuberculosis in Mejia canton, a major dairy cattle production region in Ecuador. Randomly selected cattle (1,012 from 59 farms) classified according to herd size were tested by the single tuberculin test (STT). Sixty days later, positive reactors were tested again by the comparative tuberculin test (CTT). In addition, tissue samples from two STT-CTT-positive reactors detected on a farm were obtained in a local slaughterhouse and analyzed bacteriologically. A total of 4.24% of the cattle were positive in the STT and 3.85% were positive in the CTT, with the highest number (7.95%) in large herds versus 3.4% in medium herds and 0.3% in small herds. Mycobacterium bovis was isolated from mesenteric lymph nodes and lungs of one animal. A 16S ribosomal RNA-based polymerase chain reaction confirmed culture results and differentiated mycobacteria other than M. tuberculosis. This study confirms the zoonotic importance of tuberculosis in Ecuadorian dairy cattle with herd size likely to be a crucial parameter in the prevalence of the disease. The implementation of a national control program is necessary and should be based on the detection of positive cattle by STT in combination with CTT.