Resistance Evolution

"I just happened to have a discussion about creation v evolution today at work. One said ' in every example of change (evolution) we can observe, there is always a loss or destruction of DNA, not a gain in information.' But we can't really watch evolution changes? He said that when viruses or bugs get resistant to vaccines, that the vaccine killed some strains and the rest just kept living, so really it wasnt evolution but that the remaining viruses lost some DNA, so change occurred but it wasnt forward progressive change but backward less developed change. How do you answer that?"

First of all, every change in the genome that we see is not a loss or destruction of DNA. Some changes are destruction, but large losses in DNA will lead to cell death, and not to evolution. Usually we see small changes in the DNA sequence. Considering the vast amount of changes that happen during every replication, the vast majority will have no effect whatsoever on the organism. However, sometimes a small change can lead to a difference in survival for that organism that allows it to reproduce more offspring and leave its DNA for the next generation in greater quantity (this is Natural Selection).
As for the vaccine- and antibiotic-resistant viruses and bacteria, this is a type of selection, though artificial and caused by us. The DNA (or RNA in some viruses) will change through reproduction and cell division just as it does in our own cells. However, in this case, somewhere along the way one of these changes led to a difference in survival- which is that it is resistant to whatever the antibiotic or vaccine is. What happens in the body is that the doctor will kill off all of the virus or bacteria that is not resistant, which leaves only the resistant copies to reproduce. During this process, only the genes from the resistant strain get passed on, and therefore, only resistant survive in the body. That is how we end up with resistant strains taking over populations, and it is excelerated because we are killing off all the non-resistant competitors.