This question involves the elements called plasmids that we have learned about in this chapter.
Question A: There are several possibilities that can explain why some students were sick and others not. The simplest and easiest possibility is that the student that became sick had not been vaccinated against diphtheria with the DTaP vaccine. It is also possible that the vaccination may have failed in these students. From a genetic perspective, the strain of diphtheria in the sick student may have mutated from that in the healthy students thereby eluding the protection offered by the vaccine. Another possibility is that the organisms in the healthy students had not undergone transduction to obtain the plasmid that carries the genes for the production of diphtheria toxin. Recall that to produce the toxin diphtheria organisms must obtain the genes for the toxin. These are passed to the pathogen by transduction of the bacteria by bacterial viruses in the process known as transduction.
Question B: The first thing to do would be to determine if the students that became ill were vaccinated. If they were, then there is the potential that a new and different strain of Corynebacterium diphtheriae is present and that could potentially be a public health hazard. The second problem is that the vaccine that these student were given was ineffective. If all of them were given the same vaccine that lot of vaccine would have to be tested for effectiveness.
There are ways in which DNA can be manipulated to inhibit the growth of organisms. This question involves those methods and also mutations that can occur in bacteria.
Question A: Ultraviolet light will cause the formation of thymine dimers. These dimers prevent the replication of DNA and as such will inhibit the growth of bacteria. Using this light prevents the growth of organisms that may have found their way into the hood thereby keeping it sterile.
Question B: Bacteria have mechanisms that can excise thymine dimers. These methods are commonly seen in many bacteria. Therefore, the use of the UV light may not completely protect against bacterial growth indefinitely.
Question C: The illness of the previous technician could be the result of poor aseptic technique in which he contaminated himself with a potentially pathogenic organism.