Intraspecies differentiation of strains of Mycobacterium tuberculosis obtained from Czechoslovakian, Mongolian and South Indian patients

Twenty nine strains of M. tuberculosis from Czechoslovakia, 46 from Mongolia and 50 from South India were tested for virulence in the guineapig, sensitivity to thiophen-2-carboxylic acid hydrazide (TCH) and phage type. Most of the Czechoslovakian and Mongolian strains (93 and 80% respectively) were highly virulent in the guineapig while only 36 per cent of the South Indian strains showed high virulence. Similarly very high proportions of Czechoslovakian (97%) and Mongolian strains (85%) were resistant to TCH as against only 22 per cent of South Indian strains. The phage type I was observed in none of the Czechoslovakian strains, 4 per cent of Mongolian strains and in 68 per cent of South Indian strains. Thus, the Czechoslovakian and Mongolian strains, in general, resembled the classical M. tuberculosis, while the South Indian strains were generally of low virulence, susceptible to TCH and of phage type I. Evidence accumulated over the last two decades has shown that there exist within the species Mycobacterium tuberculosis, some variants and types on a subspecies level. The most prominent of these, the South Indian variant of M. tuberculosis, is distinguished by a number of characteristic features viz., lower virulence in the guineapig, enhanced susceptibility to hydrogen peroxide and thiopen-2-carboxylic acid hydrazide (TCH), natural resistance to thioacetazone and p-amino salicylic acid, clustering into an intermediate phage type I and characteristic composition of cell wall lipids1-5. Howeve

Increased detection by restaining of acid-fast bacilli in sputum samples transported in cetylpyridinium chloride solution

SETTING: Seventeen health facilities in a Tuberculosis Unit, and the Tuberculosis Research Centre (TRC), Chennai, India. AIM: Evaluation of restaining by the auramine-phenol method for detection of acid-fast bacilli (AFB) in direct smears of samples transported in cetylpyridinium chloride (CPC) solution. METHODS: Among patients attending the above health facilities, 730 samples were collected in CPC and transported to the TRC. Two direct smears were prepared from each sample, one stained by the usual auraminephenol method (primary staining) and the other stained again by the same method (restaining) for examination by fluorescence microscopy. All the samples were processed for culture of Mycobacterium tuberculosis. RESULTS: A significantly higher proportion (49.6%) of samples were positive by restaining compared to primary staining (32.5%, P � 0.0001). Of 362 samples positive by restaining, 38.7% were negative by primary staining. The yield of different grades of smears was significantly higher with restaining than with primary staining (P � 0.0001). More smear-negative culturepositive smears were observed with the primary than with the restaining method (178/400 [44.5%] vs. 78/ 400 [19.5%], P � 0.001). CONCLUSION: The rate of detection of AFB in direct smears made from sputum samples transported i