Detecção do Fator Corda: utilização de diferentes metodologias com e sem coloração para uma rápida identificação presuntiva do complexo Mycobacterium tuberculosis

Abstract

The quick differentiation between M. tuberculosis and Nontuberculous Mycobacteria is essential for the adequate treatment of patients, mainly those that are coinfected with the Human Immunodeficiency Virus or patients with basal respiratory diseases, such as: cystic fibrosis and previous pulmonary sequels. The identification by basic and molecular methods can be used; however, such a use requires primarypresumptive identification to know which protocol should be followed. Hence, the purpose of this study was to evaluate different methodologies, with and without coloration, in the Cord Factor detection, to enable a quick presumptive identification of Mycobacterium tuberculosis Complex. Sputum smears were colored by the Ziehl- Neelsen method after processing and centrifugation, being then evaluated for presence of Cord Factor. Two smears from colonies isolated from LowensteinJensen medium were colored on slides by the Ziehl-Neelsen method and Auramine O, and viewed in the microscope at white and fluorescent light, respectively; and a smear was viewed directly in the microscope under uncolored inverted light, for the Cord Factor detection. For the species identification, basic biochemical tests were utilized as golden standard. Two observers developed all methodologies in a blindedmanner. Out of the 21 sputum smears, 10 (47.6%) were detected as having the Cord Factor, corresponding so to 100% of sensitivity and specificity. Out of the 101 cultures of mycobacteria colored by the Zielh-Neelsen technique, 88 (87.1%) were detected as having the Cord Factor; which corresponds to a sensitivity of 100%; specificity of 81.3%; positive predictive value of 96.6%; negative predictive value of100%; accuracy of 97.0% and Kappa = 0.88 (very good concordance - CI95%). By the Auramine coloration, 89 (88.1%) out of 101 smears exhibited the Cord Factor, corresponding so to a sensitivity of 100%; specificity of 75.0%; positive predictive value of 95.5%; negative predictive value of 100%; accuracy of 96.0% and Kappa = 0.83 (very good concordance - CI95%). Without coloration, by direct viewing, andusing the microscope under inverted light, 90 (89.1%) out of 101 smears have shown the Cord Factor, corresponding so to a sensitivity of 100%; specificity of 68.8%; positive predictive value of 95.5%; negative predictive value of 100%; accuracy of 95% and Kappa = 0.79 (good concordance - CI95%). The specificity achieved 100% when associated to observation of colonies characteristics within the culture medium. There was a high results agreement between both observers. The Cord Factor detection for presumptive identification of mycobacterium tuberculosis complex hasan excellent accuracy, as in case of direct coloration of sputum, as in case of positive colonies colored by Ziehl-Neelsen and Auramine methodologies, or even without any coloration, if viewed in the microscope at white, fluorescent, or inverted light, respectively; e could be utilized to guide the definitive identification methodologies in mycobacteria laboratories. The uncolored methodology is quicker, but depends on effective technical training. It is important to highlight that there are no works described in the literature, comparing Cord Factor detection methodologies; however, it is necessary that other laboratories develop their own experiences, in order to enable new researches and comparisons.