Question

Thanks!!

1 pts D Question 2 Explain how the bacterium is attenuated in the Vivotif vaccine and why this attenuation prevents the the bacteria in the vaccine from causing typhoid fever. (Note: You will find the answer in the product insert for the drug under "Clinical Pharmacology." Be specific and thorough in your response.) HTML Editor? ? , Paragraph o words

Answer 1

The S. typhi vivotif an oral vaccine, derived by chemical mutagenesis, is deficient in activity of the gal E gene product, which restricts its ability to produce complete lipopolysaccharides. In addition,vivotif have several nutritional auxotrophies, that are approximately half the growth rate of the parent strain Ty2, does not produce H2S, and lacks the Vi antigen .Vivotif grown in the presence of low concentrations of galactose, is immunogenic, suggesting that the uptake of galactose by vivotif enables production of lipopolysaccharide, leading to immunogenicity. It has been presumed that an oversupply of galactose results in accumulation of toxic metabolites within the bacterial cells leading to bacterial lysis. Attenuation and safety of Ty21a has been presumed to be due to the combination of gal E mutation and the lack of Vi antigen. However, an analogous mutant (Vi negative, gal E deletion mutant) of S. typhi prepared by recombinant DNA techniques has been shown to be virulent. In addition, galactose induced lysis of vivotif is inhibited in vitro in the presence of glucose. Therefore, the combination of gal E and Vi mutations does not account for the safety of Ty21a or for the failure to recover vaccine organisms from people ingesting the usual dose. Vivotif is attenuated by an incompletely understood mechanism.