Over the past several years doctors have determined that  penicillin
was not killing the bacteria that cause the ear infection in children.
Why is this an example of evolution? What is the selecting agent in
this case? Explain what happened to the DNA of the bacteria.

Hi! Thanks for the interesting question.

Please take note that the information provided here is being debated
upon by opposing views regarding these issues. I will provide small
snippets from the articles I will cite but I highly recommend that you
read them in their entirety to get a more comprehensive understanding.

Our first link from the University of Wisconsin-Madison provides an
explanation to the evolution of bacteria in terms of its resistance to
penicillin including its genetic interactions.

a. Inherent (Natural) Resistance – “Bacteria may be inherently
resistant to an antibiotic.”

b. Acquired Resistance – “Bacteria can develop resistance to
antibiotics, e.g. bacterial populations previously-sensitive to
antibiotics become resistant. This type of resistance results from
changes in the bacterial genome.”

The types of resistance can be traced to vertical evolution and
horizontal evolution.

1. Vertical Evolution – “strictly a matter of Darwinian evolution
driven by principles of natural selection: a spontaneous mutation in
the bacterial chromosome imparts resistance to a member of the
bacterial population. In the selective environment of the antibiotic,
the wild type (non mutants) are killed and the resistant mutant is
allowed to grow and flourish.”

2. Horizontal Evolution – “the acquisition of genes for resistance
from another organism. For example, a streptomycete has a gene for
resistance to streptomycin (its own antibiotic), but somehow that gene
escapes and gets into E. coli or Shigella.”

Interaction in the DNA of the bacteria are seen as:

“Bacteria are able to exchange genes in nature by three processes:
conjugation, transduction and transformation. Conjugation involves
cell-to-cell contact as DNA crosses a sex pilus from donor to
recipient. During transduction, a virus transfers the genes between
mating bacteria. In transformation, DNA is acquired directly from the
environment, having been released from another cell.”

In order to get a better understanding please read the whole article.

“Bacterial Resistance to Antibiotics”
http://www.bact.wisc.edu/microtextbook/ControlGrowth/resistance.html 

On the other side of the spectrum, the Creation theorist contend the
following:

“Resistance does not come about by haphazard mutations developing
genetic material to code for one or another means of resistance, but
from genetic material that has always existed in the bacteria's gene
pool ever since its Divine creation.”

“These independently moving portions of DNA cannot be considered new
genetic material, because they do not add anything new to the genetic
capacity of the organism, and may actually be harmful. Similar things
take place in human DNA and there are many heartbreaking examples of
deleterious effects in children related to these kinds of mutations,
some of which Dr. Anita Millen showed in her presentation at our
September 1992 meeting, such as Fragile X Syndrome, Cri du Chat
Syndrome, and the various trisomies, e.g., Downs Syndrome.”

“What must not be overlooked, is not whether an organism can become
resistant to an antibiotic, but whether an organism can develop new
genetic material, independent of human intervention, that will give it
new capabilities that will raise it to the status of a "higher" life
form. This is what has never been demonstrated but must be if
evolution is to be proven true.”

“Does Emergence of Antibiotic-Resistant Bacteria Prove Evolution?”
By Jon A. Covey, BA, MT(ASCP)
http://www.creationinthecrossfire.com/Articles/AntibioticResistance.html

“Some antibiotic resistance was already present in the bacterial
population, as shown by specimens frozen before the development of
antibiotics. So natural selection only selected from pre-existing
variation. But nothing new was produced. Similarly,
myxomatosis-resistant rabbits were already present in the population.
When myxomatosis was introduced to Australia, non-resistant rabbits
were selected against. But this processes caused the loss of
information from the bacteria and rabbit population due to the loss of
genetic diversity.”

“Has evolution really been observed?”
http://www.answersingenesis.org/docs/508.asp 

The next articles are additional resources that may be of help to you
as regards to this discussion.

“BACTERIAL ANTIBIOTIC RESISTANCE—PROOF OF EVOLUTION?”
by Bert Thompson, Ph.D.
http://www.apologeticspress.org/rr/rr1994/r&r9408b.htm 

“The Evolution of Resistance to Penicillin”
Susan Streble 
http://webpub.allegheny.edu/employee/r/rmumme/FS101/ResearchPapers/SusanStreble.html

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Regards,  
Easterangel-ga
Google Answers Researcher

very interesting article(s). I  have learned a lot from  the
information that you have provided me with. Thank you.

It is an example of evolution because the bacterium is evolving to be
better able to survive in a changing environment.
The selection agent is the penicillin.
Several possibilities exist that might explain the change, not
necessarily involving any change in DNA.
First, a pre-existing variant within the population may have had a
greater tolerance of penicillin, and survived to replicate where
others did not - the definition of "selection".
It is "possible" that a new mutation occurred in a gene whose protein
product is required for the toxicity of penicillin to work.  This
would then have been selected.
It is also possible - indeed perhaps likely - that a resistence gene
was introduced into the population via horizontal gene transfer on a
plasmid.  This is the basis for the upsurge in multi-resistantt staph.
aureus in hospitals.