Farnia P, Mohammadi F, Zarifi Z, Tabatabee D J, Ganavi J, Ghazisaeedi K, Farnia P K, Gheydi M, Bahadori M, Masjedi M R, Velayati A A
National Research Institute of Tuberculosis and Lung Disease (NRITLD), Shaheed Beheshti University of Medical Sciences and Health Services, Daradad, Tehran 19556, Iran.
J Clin Microbiol. 2002 Feb;40(2):508-11. doi: 10.1128/JCM.40.2.508-511.2002.
In order to try to improve the results of direct smear microscopy, we used the mucus-digesting quality of chitin in tuberculosis (TB) laboratories. For this purpose, a total of 430 sputum specimens were processed by the N-acetyl-L-cysteine concentration, sodium hypochlorite (NaOCl) liquefaction, chitin sedimentation, and direct microscopy methods. Then, the smear sensitivity for acid-fast bacillus detection by chitin-treated sputum was compared with the sensitivity of smears prepared by other methods. Our results showed that the chitin solution took less time to completely homogenize the mucoid sputum than did the N-acetyl-L-cysteine and NaOCl methods. The N-acetyl-L-cysteine concentration method demonstrated sensitivity and specificity levels of 83 and 97%, respectively. In comparison, the sensitivity of chitin sedimentation was 80%, with a specificity of 96.7%. The NaOCl liquefaction method showed a sensitivity of 78%, with a specificity of 96%. Finally, the sensitivity of direct microscopy was lower than those of the other tested methods and was only 46%, with a specificity of 90%. The chitin and NaOCl liquefaction methods are both easy to perform, and they do not require additional equipment (centrifuges). Also, our results demonstrated that the chitin method is less time-consuming than the NaOCl method, since only 30 min of incubation is required to bring complete sedimentation of bacilli in chitin-treated sputum whereas the NaOCl method needs 10 to 12 h to give the same results in the same sputum specimens. Therefore, the chitin liquefaction and sedimentation method may provide better results in TB laboratories of developing countries than the N-acetyl-L-cysteine concentration, NaOCl overnight sedimentation, and direct smear microscopy methods.
为了尝试提高直接涂片显微镜检查的结果，我们在结核病（TB）实验室利用了几丁质的黏液消化特性。为此，共采用N-乙酰-L-半胱氨酸浓缩法、次氯酸钠（NaOCl）液化法、几丁质沉淀法和直接显微镜检查法对430份痰标本进行处理。然后，将经几丁质处理的痰涂片检测抗酸杆菌的敏感性与其他方法制备的涂片敏感性进行比较。我们的结果表明，与N-乙酰-L-半胱氨酸和NaOCl方法相比，几丁质溶液使黏液样痰完全均质化所需时间更短。N-乙酰-L-半胱氨酸浓缩法的敏感性和特异性水平分别为83%和97%。相比之下，几丁质沉淀法的敏感性为80%，特异性为96.7%。NaOCl液化法的敏感性为78%，特异性为96%。最后，直接显微镜检查法的敏感性低于其他测试方法，仅为46%，特异性为90%。几丁质和NaOCl液化法操作都很简便，且不需要额外设备（离心机）。此外，我们的结果表明，几丁质法比NaOCl法耗时更少，因为经几丁质处理的痰中，只需30分钟孵育就能使杆菌完全沉淀，而同样的痰标本采用NaOCl法需要10至12小时才能得到相同结果。因此，在发展中国家的结核病实验室中，几丁质液化和沉淀法可能比N-乙酰-L-半胱氨酸浓缩法、NaOCl过夜沉淀法和直接涂片显微镜检查法能提供更好的结果。
