Dehydrated egg to replace “in natura” egg in the preparation of Löwenstein-Jensen medium for mycobacteria culture

Abstract

 Bacteriological methods are the most important to diagnose pulmonary tuberculosis. The culture medium most used to isolate mycobacteria is Löwenstein-Jensen (LJ), which is a solid medium containing eggs, glycerol and asparagine as carbon and nitrogen source. The eggs used to prepare the medium need a previous cleaning, consisting of brushing with water and soap, and decontamination with 70% alcohol during 30 minutes. This procedure takes time; besides it is not so simple to organize the acquisition of fresch eggs. With the purpose of simplifying the whole procedure of making medium, we propose the replacement of “in natura” by dehydrated eggs. This study compares the performance of conventional LJ and LJ made with dehydrated eggs. Clinical specimens sent to the laboratory for tuberculosis diagnosis were decontaminated by Petroff method and inoculated in tubes of conventional LJ and the test LJ. It was used 200 clinical specimens, 150 were smear positive and 50 smear negative. Among the 150 samples smear positive 123 were positive in traditional LJ and 24 were culture negative, while in the test LJ 121 were positive and 26 were negative. The difference was not significant. Three cultures were contaminated in both media. Comparison of the two media showed a sensibility of 98% and specificity of 100% The conclusion is that the dehydrated egg could be an alternative way to make LJ medium, propitiating a simpler and more practical medium preparation.