Revisiting susceptibility testing in MDR-TB by a standardized quantitative phenotypic assessment in a European multicentre study.

OBJECTIVES: Treatment outcome of MDR-TB is critically dependent on the proper use of second-line drugs as per the result of in vitro drug susceptibility testing (DST). We aimed to establish a standardized DST procedure based on quantitative determination of drug resistance and compared the results with those of genotypes associated with drug resistance. METHODS: The protocol, based on MGIT 960 and the TB eXiST software, was evaluated in nine European reference laboratories. Resistance detection at a screening drug concentration was followed by determination of resistance levels and estimation of the resistance proportion. Mutations in 14 gene regions were investigated using established techniques. RESULTS: A total of 139 Mycobacterium tuberculosis isolates from patients with MDR-TB and resistance beyond MDR-TB were tested for 13 antituberculous drugs: isoniazid, rifampicin, rifabutin, ethambutol, pyrazinamide, streptomycin, para-aminosalicylic acid, ethionamide, amikacin, capreomycin, ofloxacin, moxifloxacin and linezolid. Concordance between phenotypic and genotypic resistance was >80%, except for ethambutol. Time to results was short (median 10 days). High-level resistance, which precludes the therapeutic use of an antituberculous drug, was observed in 49% of the isolates. The finding of a low or intermediate resistance level in 16% and 35% of the isolates, respectively, may help in designing an efficient personalized regimen for the treatment of MDR-TB patients. CONCLUSIONS: The automated DST procedure permits accurate and rapid quantitative resistance profiling of first- and second-line antituberculous drugs. Prospective validation is warranted to determine the impact on patient care.

Evaluation of a biphasic media assay for pyrazinamide drug susceptibility testing of Mycobacterium tuberculosis.

OBJECTIVES: Pyrazinamide is a key first-line tuberculosis drug. Reliable drug susceptibility testing (DST) data are of clinical importance, but in vitro testing is challenging since the activity of pyrazinamide is pH sensitive. The BACTEC MGIT 960 is considered the principal reference technique, but Wayne's test is an alternative, although it may be difficult to interpret. A further alternative is the use of a biphasic media assay (BMA). The objective of this work was to evaluate the BMA against the MGIT method and with screening of pncA gene mutations. METHODS: Twenty strains were inoculated in tubes containing 2 mL of Löwenstein-Jensen (LJ) medium and 2 mL of semi-solid Kirchner medium with a critical concentration of 66 mg/L pyrazinamide at a pH of 5.2 or 5.5, incubated for 2 weeks and visually read. The results obtained were compared with MGIT 960 and DNA sequencing. RESULTS: Results were obtained in duplicate for 19 strains. One strain failed to grow on two occasions and only one result was available. Reproducibility was 95%. Eleven of the 19 strains were susceptible to pyrazinamide, whereas 7 were resistant. One strain was susceptible initially and pyrazinamide resistant on repeat testing. At pH 5.5, two strains reported as susceptible at pH 5.2 gave resistant results. CONCLUSIONS: The BMA might serve as a reliable low-cost DST alternative for pyrazinamide, particularly in laboratories using locally made solid media for DST. Its major drawback is the time to result. A reliable and affordable test method for the detection of pyrazinamide resistance is needed, especially in settings where multidrug-resistant tuberculosis is increasing. Proficiency testing should be routinely introduced wherever pyrazinamide DST is performed.

Rifampicin-resistant and rifabutin-susceptible Mycobacterium tuberculosis strains: a breakpoint artefact?

OBJECTIVES: It has long been assumed that some rifampicin-resistant Mycobacterium tuberculosis strains are susceptible to, and thus treatable with, rifabutin. However, clinical breakpoints for susceptibility testing of rifabutin as well as the evidence for a clinical effect of rifabutin in rifampicin-resistant strains remains poorly defined. The objective of this study was to re-evaluate the breakpoint for rifabutin in relation to its MIC wild-type distribution and the presence of mutations in rpoB. METHODS: The MIC in 7H10 Middlebrook medium was determined for clinical isolates of M. tuberculosis (n = 95), where a majority were multidrug resistant. Additionally, all strains were screened for rpoB mutations by sequencing and the GenoType MTBDRplus assay. RESULTS: Rifampicin resistance was confirmed by genotypical and/or phenotypical tests in 73 isolates (76.8%). Nineteen isolates, defined as rifampicin resistant and rifabutin susceptible according to the present breakpoint, exhibited significantly higher MICs of rifabutin (0.064-0.5 mg/L) than rifabutin-susceptible isolates without any detectable mutations in rpoB (P < 0.001). These 19 isolates were clearly resistant to rifampicin (MIC 2-256 mg/L) and all but one had mutations in rpoB, with 9 (47.4%) specifically in Asp516Val. CONCLUSIONS: Our results indicate that rifampicin-resistant but rifabutin-susceptible isolates according to the present breakpoints harbour rpoB mutations and have a rifabutin MIC significantly higher than strains without any detectable mutations in rpoB. So far there are no clinical, pharmacological or microbiological data to confirm that such isolates can be treated with rifabutin and we suggest a revision of the current breakpoints.

Reevaluation of the critical concentration for drug susceptibility testing of Mycobacterium tuberculosis against pyrazinamide using wild-type MIC distributions and pncA gene sequencing.

Pyrazinamide (PZA) is a potent first-line agent for the treatment of tuberculosis (TB) with activity also against a significant part of drug-resistant Mycobacterium tuberculosis strains. Since PZA is active only at acid pH, testing for susceptibility to PZA is difficult and insufficiently reproducible. The recommended critical concentration for PZA susceptibility (MIC, 100 mg/liter) used in the Bactec systems (460 and MGIT 960) has not been critically evaluated against wild-type MIC distributions in clinical isolates of Mycobacterium tuberculosis. Using the Bactec MGIT 960 system, we determined the PZA MICs for 46 clinical M. tuberculosis isolates and compared the results to pncA sequencing and previously obtained Bactec 460 data. For consecutive clinical isolates (n = 15), the epidemiological wild-type cutoff (ECOFF) for PZA was 64 mg/liter (MIC distribution range, ≤ 8 to 64 mg/liter), and no pncA gene mutations were detected. In strains resistant in both Bactec systems (n = 18), the PZA MICs ranged from 256 to ≥ 1,024 mg/liter. The discordances between pncA sequencing, susceptibility results in Bactec 460, and MIC determinations in Bactec MGIT 960 were mainly observed in strains with MICs close to or at the ECOFF. We conclude that in general, wild-type and resistant strains were clearly separated and correlated to pncA mutations, although some isolates with MICs close to the ECOFF cause reproducibility problems within and between methods. To solve this issue, we suggest that isolates with MICs of ≤ 64 mg/liter be classified susceptible, that an intermediary category be introduced at 128 mg/liter, and that strains with MICs of >128 mg/liter be classified resistant.

Rates and mechanisms of resistance development in Mycobacterium tuberculosis to a novel diarylquinoline ATP synthase inhibitor.

R207910 (also known as TMC207) is an investigational drug currently in clinical studies for the treatment of multidrug-resistant (MDR) tuberculosis. It has a high degree of antimycobacterial activity and is equally effective against drug-susceptible and MDR Mycobacterium tuberculosis isolates. In the present study, we characterized the development of resistance to R207910 in vitro. Ninety-seven independent R207910-resistant mutants were selected from seven different clinical isolates of M. tuberculosis (three drug-susceptible and four MDR isolates) at 10x, 30x, and 100x the MIC. At a concentration of 0.3 mg/liter (10x the MIC), the mutation rates ranged from 4.7 x 10(-7) to 8.9 x 10(-9) mutations per cell per division, and at 1.0 mg/liter (30x the MIC) the mutation rate ranged from 3.9 x 10(-8) to 2.4 x 10(-9). No resistant mutants were obtained at 3 mg/liter (100x the MIC). The level of resistance ranged from 0.12 to 3.84 mg/liter for the mutants identified; these concentrations represent 4- to 128-fold increases in the MICs. For 53 of the resistant mutants, the atpE gene, which encodes a transmembrane and oligomeric C subunit of the ATP synthase and which was previously shown to be involved in resistance, was sequenced. For 15/53 mutants, five different point mutations resulting in five different amino acid substitutions were identified in the atpE gene. For 38/53 mutants, no atpE mutations were found and sequencing of the complete F0 ATP synthase operon (atpB, atpE, and atpF genes) and the F1 ATP synthase operon (atpH, atpA, atpG, atpD, and atpC genes) from three mutants revealed no mutations, indicating other, alternative resistance mechanisms. Competition assays showed no measurable reduction in the fitness of the mutants compared to that of the isogenic wild types.

Wild-type MIC distributions for aminoglycoside and cyclic polypeptide antibiotics used for treatment of Mycobacterium tuberculosis infections.

The aminoglycosides and cyclic polypeptides are essential drugs in the treatment of multidrug-resistant tuberculosis, underscoring the need for accurate and reproducible drug susceptibility testing (DST). The epidemiological cutoff value (ECOFF) separating wild-type susceptible strains from non-wild-type strains is an important but rarely used tool for indicating susceptibility breakpoints against Mycobacterium tuberculosis. In this study, we established wild-type MIC distributions on Middlebrook 7H10 medium for amikacin, kanamycin, streptomycin, capreomycin, and viomycin using 90 consecutive clinical isolates and 21 resistant strains. Overall, the MIC variation between and within runs did not exceed +/-1 MIC dilution step, and validation of MIC values in Bactec 960 MGIT demonstrated good agreement. Tentative ECOFFs defining the wild type were established for all investigated drugs, including amikacin and viomycin, which currently lack susceptibility breakpoints for 7H10. Five out of seven amikacin- and kanamycin-resistant isolates were classified as susceptible to capreomycin according to the current critical concentration (10 mg/liter) but were non-wild type according to the ECOFF (4 mg/liter), suggesting that the critical concentration may be too high. All amikacin- and kanamycin-resistant isolates were clearly below the ECOFF for viomycin, and two of them were below the ECOFF for streptomycin, indicating that these two drugs may be considered for treatment of amikacin-resistant strains. Pharmacodynamic indices (peak serum concentration [Cmax]/MIC) were more favorable for amikacin and viomycin compared to kanamycin and capreomycin. In conclusion, our data emphasize the importance of establishing wild-type MIC distributions for improving the quality of drug susceptibility testing against Mycobacterium tuberculosis.

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)

The added value of a European Union tuberculosis reference laboratory network--analysis of the national reference laboratory activities.

National reference laboratories (NRL) and other laboratories are the cornerstones of well-functioning tuberculosis programmes and surveillance activities. However, the scope and activity of NRL services for mycobacterial identification and drug susceptibility testing (DST) has not been examined in detail across the European Union (EU), nor has the added value of cooperation and networking at the European level been explored with regard to strengthening laboratory services. Therefore, the European Centre for Disease Prevention and Control (ECDC) has commissioned a survey to explore these issues and to identify areas of work that could bring added value by supporting networking activities of tuberculosis (TB) reference laboratories in the EU. Structured questionnaires were sent to TB reference laboratory experts in the EU and European Economic Area (EEA) countries, and in three additional countries selected on the basis of their networking activities with EU projects and other initiatives (Switzerland, Croatia and Israel). The compiled results describe the activities and structure of 32 NRLs (29 countries replied, a response rate of 91%). The analysis of the survey led to the following recommendations for strengthening TB laboratory services: (1) implementing of the published European standards for TB laboratory services with respect to infrastructure, national reference functions, biosafety, human resources, quality assurance, operational research (including evaluation of new medical diagnostics), accuracy and speed, appropriately trained staff; (2) ensuring that laboratories only perform activities for which they have demonstrated proficiency; (3) implement validated and standardised second-line drug susceptibility testing (DST), including drugs used to define extensively drug-resistant tuberculosis (XDR TB); (4) aiming to identify Mycobacterium tuberculosis complex (MTBC) and rifampicin (RIF) resistance in over 90% of cultures and cases from smear-positive sputum directly within one to two working days. To realise some of the above recommendations and to strengthen links of TB surveillance and microbiology activities in the EU, a list of suggested generic areas of activities for an EU network of reference laboratories is presented. Such a network would build on and link to existing networks and initiatives at the European and global level.

Antimicrobial susceptibility testing of Mycobacterium tuberculosis (EUCAST document E.DEF 8.1)--report of the Subcommittee on Antimicrobial Susceptibility Testing of Mycobacterium tuberculosis of the European Committee for Antimicrobial Susceptibility Testing (EUCAST) of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID).

This review describes the methods available for drug susceptibility testing of Mycobacterium tuberculosis. The methods have been developed over several decades and are restricted to specialised centres in most European countries, as they are technically demanding, require appropriate isolation facilities and can be difficult to interpret. The absolute concentration, resistance ratio and proportion methods can all give accurate results, provided that they are carefully quality-controlled and standardised. Automated rapid culture and molecular methods have been evaluated at large reference centres and in multicentre collaborations, and perform well for testing susceptibility to most first- and second-line anti-tuberculosis drugs. Accuracy is more important than rapid testing, and this is most reliably achieved if drug susceptibility tests are done in a small number of well-equipped, experienced laboratories that participate and perform well in an international drug susceptibility testing quality assessment scheme. The WHO Supranational Laboratory Quality Control Network offers a global scheme that assesses the ability of participating laboratories to identify isoniazid, rifampicin, ethambutol and streptomycin resistance. Second-line drug resistance testing is currently being standardised, and such testing should only be performed at the national reference laboratories in western and central European countries because of the relatively small number of cases and the concomitant difficulty of maintaining testing proficiency in multiple centres performing small numbers of tests. There is a need to expand international external quality assessment to include second-line drug susceptibility testing.

Rhodococcus and Mycobacterium Tuberculosis: masquerade or mixed infection.

Rhodocci have a morphology similar to that of Mycobacterium tuberculosis (TB), and are indistinguishable from normal diphtheroid flora. Symptoms include fever, productive/non-productive cough and pleuritic chest pain. Rhodococcal infections, being resistant to routine anti-tuberculosis medications, may be misdiagnosed as drug-resistant TB, thus prompting treatment for TB with rifampicin-containing regimens that promote the emergence of resistance. We present here a sputum smear AFB-positive case who, although clinically cured, remains unresolved despite a series of technological investigations as to the cause of infection being purely rhodococci or mixed infection with M. tuberculosis.

Molecular Epidemiology of Mycobacterium Tuberculosis Strains in the North-West and West of Iran.

BACKGROUND: Identifying Mycobacterium tuberculosis (MTB) transmission type is a key step in the control of this disease. AIM: This study aimed to determine the path and transmission type of MTB and the insertion sequence IS6110 band number and verify their relationship to demographic and clinical risk factors. SUBJECTS AND METHODS: In this cross-sectional study, 64 MTB patients from three border provinces of Iran were selected after full clinical history and physical evaluation design. The drug susceptibility testing was carried out using the standard proportion technique on sputum samples. Isolates tested with restriction fragment length polymorphism technique used IS6110. RESULTS: Recent transmission of disease was 33/50 (66%) based on clustering rate. The IS6110 band number had a significant relationship with drug resistance detected in proportion method tested by univariate linear regression (P < 0.01). Furthermore, the IS6110 band number had association with Bacillus Calmette-Guérin vaccination history (P = 0.02), sex (P < 0.01), and purified protein derivative (PPD) reaction size (P < 0.01) tested by multiple analysis. The risk of recent transmission inferred from the clustering rate was significantly higher in patients from Western provinces compared to those from the North-West province (P = 0.048). However, age (P = 0.39), gender (P = 0.16), vaccination history (P = 0.57), drug susceptibility, and PPD (P < 0.6) were independent of clustering. The largest cluster of up to six subjects was found in the Western provinces. CONCLUSION: Recent MTB transmission was much more common in the West compared to the North-West of Iran. Large MTB clusters with strong epidemiological links may be reflective of a disease outbreak. Correlation noted between the IS6110 band number and vaccination history; PPD size and female gender necessitates further studies.

Nosocomial Legionnaires' disease following renal transplantation.

A cluster of five cases of Legionnaires' disease in renal transplant patients is described. They were treated with erythromycin and rifampicin, and all five survived. Two of them had rejected their grafts prior to their Legionella pneumonia; two rejected their transplants after reduction of immunosuppressive therapy to combat the infection. L pneumophila was present in the water distribution system of the hospital. Eradication measures included flushing the water pipes to the transplantation ward with hot and hyperchlorinated water, raising the warm water temperature to 60 degrees C, and installing ultraviolet (UV) irradiation units on the warm and cold water pipes to the ward. These measures were successful in that no new cases of legionellosis occurred after wards. L pneumophila could subsequently not be demonstrated by culture in plastic shower hoses supplied with UV-irradiated water. L pneumophila could be demonstrated by direct fluorescent antibody technique, but nonspecific reactions cannot be excluded. A higher prevalence of elevated L pneumophila antibody titers was observed in patients nursed for more than four weeks in the hospital than in patients with a shorter hospital stay, in hospital staff members, or in the general population. It seems that, with appropriate control measures, transplantation activities need not be discontinued in the presence of a minor cluster of Legionnaires' disease in renal transplant patients.

Drug-resistant Mycobacterium tuberculosis and atypical mycobacteria isolated from patients with suspected pulmonary tuberculosis in Honduras.

BACKGROUND: Tuberculosis is a major health problem in Central America. In Honduras, with an incidence rate of 81/100,000, it is an increasingly common cause of morbidity and hospitalization. This study was conducted to examine drug-resistant tuberculosis and prevalence of infection with atypical mycobacteria in Honduran patients with suspected pulmonary tuberculosis. METHODS: Pulmonary specimens from 235 Honduran patients with suspected tuberculosis were examined by acid-fast smears and culture. The 95 mycobacterial strains isolated were identified to species level and drug susceptibility tests were carried out. Resistant Mycobacterium tuberculosis strains were tested for susceptibility to six additional drugs. Their possible relationship was studied by DNA restriction fragment length polymorphism. RESULTS: Drug-resistant strains were found in 13 of 85 culture-verified tuberculosis patients, including 10 with isolates of multidrug-resistant bacteria. Seven of the patients with multidrug-resistant tuberculosis had smear-positive disease. Nine of them had a history of specific therapy. Two patients with drug-resistant disease were shown to be infected by identical strains. Only one of 11 HIV-positive patients had drug-resistant tuberculosis. Most resistant strains were susceptible to ciprofloxacin, amikacin, kanamycin, and pyrazinamide. Atypical mycobacteria were isolated from 10 patients with suspected tuberculosis. Seven of them were receiving antituberculosis chemotherapy and five had smear-positive samples. CONCLUSIONS: These results illustrate the importance of mycobacterial culture and subsequent species identification and in vitro susceptibility testing for identification of patients with drug-susceptible or drug-resistant tuberculosis and those infected or colonized with other mycobacteria.

Multiple serovars of Mycobacterium avium complex in patients with AIDS.

Mycobacterium avium complex (MAC) was isolated and serotyped from 127 samples from 43 HIV-infected patients with disseminated disease in Sweden. Thirteen different serovars were observed. Serovar 6 was the most common, followed by 4, 9 and 11. Serovar 8 was rare. In 22 of the patients the same serovar was found in blood and at other sites. Clinical symptoms and outcome were compared in patients with different serovars. Analysis of patient records revealed no association between clinical picture and any specific serovar. The median survival time after MAC infection was 7 months. Somewhat shorter survival was observed in patients with serovar 4 than in those with serovar 6.

Improved detection of Mycobacterium avium complex with the Bactec radiometric system.

A reconsideration of the laboratory methods used for primary isolation of mycobacteria other than Mycobacterium tuberculosis is needed due to the increasingly recognized importance of such mycobacterial infections in immunocompromised patients. One example of this is the severe opportunistic infections caused by Mycobacterium avium complex among AIDS patients. In this study, the Bactec radiometric system was compared to conventional culture on solid medium for the detection of M. avium complex in 3,612 selected clinical specimens, mainly of extrapulmonary origin. Of a total number of 63 M. avium complex isolates, the Bactec system detected 58 (92%), compared to 37 (59%) for conventional culture. A much more rapid detection was attained with radiometric technique than with conventional culture. The mean detection time for the cultures positive with both methods was 7.1 and 28.3 days, respectively. The Bactec radiometric system achieves a rapid and significantly more sensitive detection and seems to be an excellent complement to conventional culture in the laboratory diagnosis of infections with the M. avium complex.

Synergistic antimycobacterial activity between ethambutol and the beta-lactam drug cefepime.

The activity of cefepime alone and in combination with ethambutol was assessed, using the BACTEC radiometric system, on 33 mycobacterial strains, 14 Mycobacterium avium complex (MAC), 6 isolates of M. malmoense, and 13 multidrug-resistant (MDR) isolates of M. tuberculosis. All tested mycobacteria were resistant to 8 mg/l cefepime. However, at a concentration of 32 mg/l cefepime was active on 7/13 (54%) MDR isolates of M. tuberculosis and 2/6 (33%) M. malmoense strains. All MAC strains were also resistant to this concentration. Synergistic antimycobacterial effects were seen for the combination of cefepime and ethambutol against all isolates of MAC and M. malmoense and on 4/13 (31%) MDR M. tuberculosis isolates. Moreover, this drug combination rendered 17/24 (71%) initially resistant mycobacterial strains susceptible. These promising results suggest that the antimycobacterial activity of combinations of beta-lactam drugs and ethambutol should be studied further.

A biphasic system for primary isolation of mycobacteria compared to solid medium and broth culture.

A biphasic culture system, the MB Check, was compared with conventional culture on Löwenstein-Jensen egg (LJ) solid medium and with Bactec broth culture for primary isolation of mycobacteria from clinical samples. A total of 104 mycobacterial isolates was detected from 985 samples examined by the three methods. The most sensitive primary isolation was with LJ culture and MB Check; these methods detected 93% and 87% of all positive cultures, respectively. MB Check allowed a somewhat more rapid detection than LJ culture. The presence of atypical mycobacteria was demonstrated most rapidly with the Bactec system.

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.

In vitro activity of thiacetazone on mycobacterial species belonging to the Mycobacterium tuberculosis complex.

Thiacetazone, despite frequent side-effects, may still be considered for the treatment of new tuberculosis cases when there is a shortage of drugs and for the management of multidrug-resistant tuberculosis. Fifty-four strains of M. tuberculosis complex were characterised based on the minimum inhibitory concentration (MIC) of thiacetazone and the growth pattern in the presence of different concentrations of the drug. The results showed that the MIC of thiacetazone to type II M. africanum strains was significantly higher than for other strains in the study (P < 0.01). Thiacetazone showed a paradoxical effect on 63% of strains where lower concentrations exhibited a better inhibiting activity than higher concentrations.