[Comparison and evaluation of Lowenstein-Jensen medium and 2% Ogawa medium for the diagnosis of tuberculosis]

Accurate diagnosis of tuberculosis is based on the detection of the bacilli in the clinical specimen. The growth of mycobacteria in laboratory media is regarded as the gold standard for diagnosis and use of two different cultivation media, one of them being a liquid one, is recommended. In this study, the diagnostic values of egg-based Lowenstein-Jensen (LJ) medium used extensively all over the world and Ogawa (2%) medium were compared. A total of 7912 pulmonary and extrapulmonary clinical samples which belonged to 3311 patients with suspected tuberculosis, were enrolled in the National Tuberculosis Reference Laboratory in Refik Saydam National Public Health Agency during 2.5 years (January 2006- June 2008). The samples were processed by modified Petroff method (4% NaOH) for homogenization-decontamination-concentration on the same day and inoculated on two Ogawa and two LJ media. The cultures were incubated at 35-37°C for eight weeks and were controlled on the third day of incubation in terms of contamination. If no contamination were detected, the cultures were incubated for a total of eight weeks with regular weekly controls. The colonies detected in culture media were identified by biochemical tests, including paranitrobenzoic acid (PNB), niacin accumulation and nitrate reduction tests. Those identified as Mycobacterium tuberculosis complex were reported as positive. The rates of contamination was 3.1% for Ogawa medium and 4% for LJ medium. Culture results were found positive for 248 patients (7.5%). While 210 of these were positive by both of the media, 20 (8.1%) patients were detected positive only by LJ and 18 (7.3%) only by Ogawa medium. The sensitivity of LJ medium was 92.7% (230/248) and of Ogawa medium was 91.9% (228/248). When LJ medium was taken as the reference method, the sensitivity, specificity, positive and negative predictive values of Ogawa medium were 91.3%, 99.4%, 92.1% and 99.4%, respectively. It was concluded that, when low price and low contamination rates were taken into consideration, Ogawa medium, used together with a liquid medium + LJ medium, would increase the yield of mycobacteria from single samples (cerebrospinal fluid, biopsy, pus, etc.) sent to the laboratories.