A new colorimetric method for rapid detection of ethambutol and streptomycin resistance in Mycobacterium tuberculosis: crystal violet decolorization assay (CVDA).

Streptomycin (STR) and ethambutol (EMB) are important drugs used for the treatment of tuberculosis. There is a need for fast, reliable and inexpensive methods for detecting resistance to these drugs. The aim of this study was to evaluate the performance of the crystal violet decolorization assay (CVDA) for the detection of STR and EMB resistance that is important drugs in tuberculosis treatment. In this study, drug susceptibility testing was performed on 140 Mycobacterium tuberculosis isolates provided from nine centers. Three tubes were used for each isolate. One of the tubes had a concentration of 2 mg/L STR and the other 5 mg/L EMB. The third was drug-free control tube. Sensitivity, specificity, positive predictive value (PPD), negative predictive value (NPD) and agreement for STR were found to be 81.8%, 94.6%, 87.8%, 91.5% and 90.57%, respectively. For EMB, sensitivity, specificity, PPD, NPD, and agreement were found to be 76%, 98.23%, 90.47%, 94.87% and 94.2%, respectively. The results were obtained in 11.3 ± 2.7 days (8-21 days). CVDA is rapid, reliable, inexpensive, and easy to perform for rapid detection of STR and EMB resistance, and it could be adapted for drug susceptibility testing.

The value of microscopic-observation drug susceptibility assay in the diagnosis of tuberculosis and detection of multidrug resistance.

Inexpensive, rapid, and reliable tests for detecting the presence and drug susceptibility of Mycobacterium tuberculosis complex (MTBC) are urgently needed to control the transmission of tuberculosis. In this study, we aimed to assess the accuracy and speed of the microscopic-observation drug susceptibility (MODS) assay in the identification of MTBC and detection of multidrug resistance. Sputum samples from patients suspected to have tuberculosis were simultaneously tested with MODS and conventional culture [Löwenstein-Jensen (LJ) culture, BACTEC MGIT™ 960 (MGIT) system], and drug susceptibility testing (MGIT system) methods. A total of 331 sputum samples were analyzed. Sensitivity and specificity of MODS assay for detection of MTBC strains were 96% and 98.8%, respectively. MODS assay detected multidrug resistant MTBC isolates with 92.3% sensitivity and 96.6% specificity. Median time to culture positivity was similar for MGIT (8 days) and MODS culture (8 days), but was significantly longer with LJ culture (20 days) (p < 0.0001 for both comparisons). Median time to availability of the susceptibility results was significantly (p < 0.0001) shorter with MODS assay (8 days) than MGIT system (20 days). In conclusion, MODS is an inexpensive and rapid test with good performance characteristics for direct diagnosis of tuberculosis and detection of multidrug resistance.

[In vitro susceptibility of Enterococcus strains to high level aminoglycosides and heavy metals]. / Enterokok suslarinin yüksek düzeyde aminoglikozidlere ve agir metallere karsi in vitro duyarliliklarinin arastirilmasi.

The widespread use of antimicrobial agents in the hospitals and environmental contamination with heavy metals are increasingly related to resistance progression in microorganisms. The aim of this study was to investigate the resistance of enterococci to high level aminoglycosides and some heavy metals [lead (Pb+2), cadmium (Cd+2), mercury (Hg+2), arsenic (As+5)]. A total of 39 Enterococcus strains, isolated from stool and rectal swabs of hospitalized patients were included to the study. Twenty of the strains were resistant to glycopeptides (11 were resistant to vancomycin + teicoplanin and 9 were resistant to only vancomycin). Disk diffusion method was performed to determine the high level resistance to aminoglycosides (gentamicin 120 microg and streptomycin 300 microg), and agar dilution method was used to detect the sensitivities of the strains against different concentrations (0.005-20 mM) of heavy metals. Since there is no specified minimum inhibitory concentration (MIC) breakpoints for heavy metals, resistance criteria described in previous studies were used. Accordingly, enterococci which exhibited MIC > or = 1 mM for lead and cadmium, MIC > or = 0.1 mM for mercury, and MIC > or = 10 mM for arsenic were accepted as resistant. High level aminoglycoside (HLAG) resistance rates were found as 91% (10/11) for vancomycin (V) + teicoplanin (T) resistant and 42% (8/19) for glycopeptide susceptible strains. While all of the isolates were resistant to lead (100%), arsenic (2.6%) and mercury (2.6%) resistance was detected in one isolate for each metal. No cadmium resistance has been detected. In our study, enterococci have exhibited seven different resistance profiles (10 strains were resistant to V + T + HLAG + Pb; 1 was resistant to V + T + Pb; 1 was resistant to V + As + Pb; 1 was resistant to HLAG + Hg + Pb; 8 were resistant to V + Pb; 7 were resistant to HLAG + Pb; 11 were only resistant to Pb). Resistance to antibiotics (aminoglycosides and/or vancomycin and/or teicoplanin) and heavy metals (lead and arsenic and/or mercury) were detected concurrently in 28 (%71.8) of the strains. It was considered remarkable that all of the isolates were resistant to lead and there was no difference between antibiotic-resistant and-susceptible strains in terms of lead resistance. In conclusion, further investigations are needed to reveal the extreme lead resistance and the relations between antibiotic and heavy metal resistances in clinical enterococcus strains.