ABSTRACT
OBJECTIVE: To evaluate the performance of blood agar for the susceptibility testing of 50 Mycobacterium tuberculosis clinical isolates against isoniazid (INH), rifampicin (RMP), streptomycin (SM) and ethambutol (EMB). DESIGN: The activity of the drugs was determined by the proportion method on blood agar instead of Middlebrook 7H10 agar according to Clinical Laboratory Standard Institute recommendations. The final concentrations of INH, RMP, SM and EMB were 0.2 microg/ml, 1 microg/ ml, 2 microg/ml and 5 microg/ml, respectively. RESULTS: The results were compared with the radiometric proportion method as the reference, and the agreements were determined as 100% for INH and RMP, 92% for SM and 96% for EMB. The specificity, sensitivity, positive predictive value and negative predictive value were 90.4% and 97.5%, 100% and 90%, 66.6% and 90% and 100% and 97.5% for SM and EMB, respectively, while these values were 100% for INH and RMP. The results of susceptibility testing were obtained on the 14th day of incubation. CONCLUSION: According to this preliminary study, our results suggest that blood agar can be used as an alternative medium for the susceptibility testing of M. tuberculosis strains against INH, RMP, SM and EMB in resource-limited countries. However, further studies are needed before implementating the method in diagnostic laboratories.
Subject(s)
Agar , Antitubercular Agents/pharmacology , Culture Media , Drug Resistance, Multiple, Bacterial , Mycobacterium tuberculosis/drug effects , Tuberculosis, Multidrug-Resistant/diagnosis , Blood , Ethambutol/pharmacology , Humans , In Vitro Techniques , Isoniazid/pharmacology , Microbial Sensitivity Tests , Mycobacterium tuberculosis/growth & development , Mycobacterium tuberculosis/isolation & purification , Rifampin/pharmacology , Tuberculosis, Multidrug-Resistant/microbiologyABSTRACT
Vancomycin-resistant enterococci (VRE) are a serious challenge for physicians because of the limited treatment options for infections caused by this organism. Prevention of VRE transmission in hospitals requires early detection of infected or colonized patients. Therefore rapid and correct detection of vancomycin resistance is essential. In this study, we use the resazurin microplate method (RMM), which is a modification of the NCCLS and BSAC broth microdilution methods to rapidly determine the susceptibilities of clinical enterococci isolates to vancomycin. The alteration in the RMM was relevant to the final bacterial count. In this method, inoculum that was 10-fold higher than standard methods was used. A total of 80 enterococci, including 11 VRE isolates and 6 vancomycin intermediate isolates, were screened with this modified colorimetric broth microdilution method. After 4 h of incubation 30 microl of 0.01% resazurin solution were added to each well and the plates were reincubated for color change for 5-10 min. The MICs were obtained at the 4th h. The results were in exact agreement with the NCCLS and the BSAC microdilution methods. Absolute and essential agreements were 100% and there were no minor, major or very major errors. In conclusion, this modified colorimetric broth microdilution method can be used as a reliable, easy, cheap and rapid method for early detection of VRE. Moreover, this method has the potential of being used to test the susceptibilities of different bacteria to other antibiotics.
