Comparison of three methods for decontamination of faeces for isolation of Mycobacterium tuberculosis

Sputum and faeces were obtained from 276 patients on admission to a study of drug resistance in Hong Kong. Acid-fast bacilli were detected microscopically in 103 (37%) sputum specimens and 135 (49%) yielded Mycobacterium tuberculosis on culture. Three methods were used to decontaminate faeces prior to dilution and culture in selective liquid Kirchner medium. A total of 61 faecal specimens were positive for M. tuberculosis on culture and, of these, pretreatment with sodium hydroxide yielded 60 (98%), Portaels modification of Wolinsky and Rynearsons's method 28 (46%) and the combined use of benzalkonium chloride and 1-hexdecylpyridinium chloride yielded 32 (52%). It is recommended that faeces should be treated with sodium hydroxide followed by dilution and culture in selective media, although it may be necessary to formulate new selective media for mycobacterial species other than M. tuberculosis.