Cholera vaccine: developmental strategies and problems.

Over a hundred years have elapsed since Vibrio cholerae, the etiological agent for the disease cholera, was discovered by Robert Koch. Ever since then serious efforts have been made to develop prophylactic measures to combat the disease without much success. Seven pandemics have so far been reported and cholera still remains a public health problem in developing countries. Several strategies have been adopted to develop vaccines against the disease and many of these vaccines have undergone field trials. During the last two decades, an enormous amount of information has accumulated regarding the organism V. cholerae, its virulence factors, including cholera toxin, and the molecular basis of its pathogenicity. In recent years, with the advent of recombinant DNA technology and major breakthroughs in molecular biology and immunology, a new dimension has been given to the design of vaccine strains. The second generation live oral vaccines will perhaps soon replace the long-used first generation parenterally administered killed whole cell vaccines which offered protection for not more than three months. All the recombinant vaccines tested so far produced adverse reactions in volunteers, although they provided varying degrees of protection upto about one year of surveillance. Parallel to the trials of live oral vaccines, combination vaccines comprising killed whole cells and purified B subunit of cholera toxin was also tried. These vaccines had minimal side-effects but the efficacy was not upto expectations. From the failure of each vaccine strain, new information had emerged and improved strategies were adopted.(ABSTRACT TRUNCATED AT 250 WORDS)

Simplified method for the detection of DNA hydrolysis by enteric campylobacters.

A simplified medium was developed for the detection of DNase produced by enteric campylobacters. Sensitivity and reproducibility of the test were similar to that of the improved toluidine blue DNA agar method. Logistically, the simplified DNA hydrolysis test was cheaper (5.5 times) than the earlier medium. Based on this study we recommend the routine use of the simplified medium to perform the DNase test for biotyping enteric campylobacters.

Comparison of selective medium supplemented with blood & a charcoal-based blood-free medium for primary isolation of campylobacters from human faeces.

A recently developed charcoal-based, blood-free selective medium-charcoal cefoperazone deoxycholate agar (CCDA) was compared with the conventional Butzler's agar (BA) for primary isolation of enteric campylobacters from human stool specimens. CCDA yielded higher percentage (93.6%) of positive isolations as compared to BA (76.6%). The rate of isolation on CCDA was significantly higher (P less than 0.0001) than on BA. Cost-wise also, the CCDA medium was two times cheaper than BA. In addition to Campylobacter jejuni and C. coli, CCDA permitted the recovery of a recently described catalase-negative campylobacters which did not grow on BA. Based on these results the routine use of CCDA is recommended, particularly in developing countries, as blood is not required for this medium.

Serotypes & biotypes of Campylobacter jejuni & C. coli from diverse sources in Calcutta.

C. jejuni and C. coli isolates from diverse sources in Calcutta were serotyped and biotyped according to the Lior scheme. Of the 55 strains examined, 85.5 per cent reacted with one or another of the 73 antisera available. This included the formation of two new serogroups, LIO 67 and LIO 76. C. coli serogroup LIO 46 biotype II was the most frequently encountered strains (14.5%), followed by C. coli serogroup LIO 29, 55 biotype II (10.5%) and C. jejuni serogroup LIO 54, biotype I (5.5%). Serogroups recovered from animals and birds were also found to be prevalent in strains isolated from clinical sources, confirming the zoonotic implications of the disease.