[Comparison of proportion method in Löwenstein-Jensen medium with the BACTEC 460 TB system for antimycobacterial...

This study was conducted to compare BACTEC 460 TB system and the proportion method in commercially available and ready to use antibiotic added Löweinstein-Jensen (LJ) medium for susceptibility testing of first line drugs in Mycobacterium tuberculosis complex isolates. A total 238 M.tuberculosis strains isolated from clinical samples in our laboratory between 2006-2010 period were included in the study. Susceptibility testing for streptomycin, isoniazid, rifampicin and ethambutol in commercially provided LJ medium (Salubris Inc., Istanbul) was performed by the proportion method as recommended by the manufacturer, and the results were compared with the results of BACTEC 460 TB (Becton Dickinson, USA) system. Resistance rates of M.tuberculosis strains against streptomycin, isoniasid, rifampicin and ethambutol obtained by BACTEC 460 TB system were 19.7%, 42%, 40.8% and 18%, respectively. Those rates were 22.7%, 38.7%, 37% and 15.5%, respectively, by antibiotic added LJ proportion method. There was no statistically significant difference between the two methods in terms of resistance rates (p> 0.05). The rates of consistency between proportion method in LJ medium and BACTEC 460 TB system for streptomycin, isoniasid, rifampicin and ethambutol susceptibility were found as 85.3%, 92.4%, 95.4% and 92.4%, respectively. When comparing the reporting time (interval between beginning of the process to reporting of the results) of the methods, minimal, maximal and average reporting spans for BACTEC 460 TB system were 5, 12 and 8.08 ± 2.65 days, and 15, 42 and 23.89 ± 6.02 days for the proportion method in LJ medium, respectively, being statistically significant (p= 0.001). It was determined that the sensitivity test results of major antimycobacterial drugs in commercial LJ medium were compatible with the BACTEC 460 TB system. Nonetheless, the rate of incompatible results was higher for STR than the other drugs. Although there has been some disadvantages such as longer reporting time, need for experience in manual processing and visual evaluation, standardized LJ media approved for quality can be used for susceptibility testing of M.tuberculosis in the laboratories which do not have eligible conditions for the establishment of automated systems.