Protection by live Mycobacterium habana vaccine against Mycobacterium tuberculosis H37Rv challenge in mice.

BACKGROUND & OBJECTIVES: In recent years the efficacy of BCG vaccine against tuberculosis has been questioned and there is no alternative vaccine available. Several strategies are being applied to get a satisfactory vaccine. Two approaches are generally considered: the subunit vaccines and the whole cell vaccines. The objective of this investigation was to evaluate an avirulent mycobacteria, Mycobacterium habana, as a whole cell vaccine to protect mice from infection of M. tuberculosis H37Rv. METHODS: AKR and immunocompromised SJL/J mice were immunized with live M. habana vaccine. These mice were challenged with M. tuberculosis H37Rv eight weeks later along with unimmunized control mice. Protection by M. habana vaccine was measured through several parameters, which included survival of challenged mice, dissemination of challenge strain and histopathology of lung tissues. RESULTS: M. habana vaccinated animals were healthier than the unvaccinated mice after challenge with M. tuberculosis and survived with significant increase in mean survival time. The viable count of challenge strain was at least 100-fold less in vaccinated mice than the control mice. The lung tissues in unvaccinated mice showed marked bronchopneumonia with clusters of acid fast bacilli, whereas vaccinated mice showed small areas of damage and evidence of protection subsequently. INTERPRETATION & CONCLUSION: It may be concluded from the evidence presented here that mice vaccinated with M. habana were protected from challenge with M. tuberculosis in both normal and immunocompromised states.

Diagnosis of tuberculous meningitis by detection of antigen and antibodies in CSF and sera.

OBJECTIVE: To evaluate diagnostic potential of three immunological tests, namely, detection of H37Rv antigen of M. Tuberculosis in CSF, detection of antibodies (IgG) against H37Rv in CSF and detection of antibodies (IgG) against H37Rv in serum for diagnosis of tuberculous meningitis in children. SUBJECTS: 50 children diagnosed as patients of tuberculous meningitis were included as cases and 48 children with CNS diseases of nontubercular etiology [pyogenic meningitis (n = 31), encephalitis (n = 10), seizure disorder of unknown etiology (n = 5), brain tumor (n = 2)] served as controls. METHODS: H37Rv antigen of M. tuberculosis was detected in CSF by Dot ELISA, and antibodies (IgG) against H37Rv in CSF and serum were detected by Plate ELISA. RESULTS: Detection of H37Rv antigen in CSF was the most sensitive (90%) and specific (95.83%) with positive and negative predictive values of 95.74% and 90.19%, respectively, followed by detection of antibodies in CSF (sensitivity-74%, specificity-89.58%, positive predictive value-88.10%, negative predictive value-76.78%). Detection of antibodies in serum had low sensitivity (50%), specificity (91.67%), positive predictive value (86.21%) and negative predictive value (63.76%). CONCLUSIONS: Detection of antigen in CSF is a rapid, sensitive and specific test for diagnosis of tuberculous meningitis in children. Detection of antibody in CSF may be useful in some cases but needs further evaluation. Detection of antibody in serum does not appear to be useful for diagnosis of tuberculous meningitis.

Genetics of cholera toxin.

Cholera is caused by the toxin secreted by Vibrio cholerae 01. Cholera toxin (CT) is a protein consisting of A and B subunits. The former contributes to intracellular toxicity whereas the B subunit is required for binding of CT to eukaryotic cell surface receptor. The structural genes encoding A and B subunits are designated as ctxA and ctxB respectively. These genes are located on the chromosome forming an operon in which ctxA precedes ctxB. The ctxAB have been cloned and sequenced. Classical strains contain two full copies of unlinked ctxAB. Most el tors have single copy. However, in some strains there are two copies which are arranged in tandem. The tandem duplication and amplification of ctxAB is controlled by a transposable element like DNA sequence called RS1. A number of genes have been identified which regulate the expression of ctx operon. V. cholerae seems to elaborate more than one toxin which are different from the one encoded by ctxAB genes.