Comparison of Three Egg-based Solid Media for Culture of Mycobacteria from Clinical Specimens

Shin, Jeong Hwan; Chang, Chul Hun; Lee, Seon Ho; Kim, Sung Ryul; Son, Han Chul; Kim, Soon Ho

Abstract

BACKGROUND: Single egg-based Ogawa medium is used for mycobacterial culture in nearly all tertiary care or medical school-affiliated hospital in Korea. However, it is expected that some mycobacteria would grow so lately or never in only one media, even if mycobacteria are present sufficiently in the specimen. To estimate the efficiency of inoculation to two or more egg-based media for isolation of mycobacteria, positive culture rates and detection time were compared among three media.
METHODS
193 clinical specimens, which referred to laboratory of Pusan National University Hospital for 2 months, including 123 specimens of patients with mycobacteriosis, were processed and inoculated to Eiken, VITE and KT media. The isolates were identified and classified to Mycobacterium tuberculosis and non-tuberculous mycobacteria (NTM) by AccuProbe method. The positive culture results were analyzed by McNemar test and t-test.
RESULTS
M. tuberculosis and NTM were isolated in 65 (34.0%) and 14 (7.4%) specimens, resulting in positive culture rates of 41.4%. Of the 123 patients' specimens, 63 cases were positive in culture of VITE media, which were significantly higher than 50 cases of Eiken and 45 cases of KT media. In 43 positive-stained specimens, twelve to twenty samples (29.3-48.8%) failed to grow in at least one media. The colonies were visible at 24.9 to 30.7 days after inoculation, and VITE and KT media detected visible colonies 4.5 and 2.5 days more rapidly than Eiken media, respectively.
CONCLUSIONS
Inoculation to two or more egg-based media is useful for increasing culture positivity and early detection of colonies for mycobacterial culture.