Download Antibiotic Resistance of Bacteria: An Example of Evolution in Action

Antibiotic Resistance of Bacteria: An Example of Evolution in Action?
by Georgia Purdom, Ph.D.
July 10, 2007
Semi-technical
The extraordinary ability of certain bacteria to develop resistance to antibiotics—which are otherwise
useful in speeding recovery from some illnesses—has been a hot topic on the minds of doctors, hospital
staff, reporters, and the general public for several years. It is also heralded as a textbook example of
evolution in action.
These bacteria are being studied by evolutionary scientists with the hope that they will reveal secrets as to
how molecules-to-man evolution could have happened.
But are bacteria really evolving?
Antibiotic-Resistant Bacteria
Antibiotics are natural substances secreted by bacteria and fungi to kill other bacteria that are competing
for limited nutrients. (The antibiotics used to treat people today are typically derivatives of these natural
products.) Scientists are dismayed to discover that some bacteria have become resistant to antibiotics
through various alterations, or mutations, in their DNA.
Hospitals have become a breeding ground for antibiotic resistant bacteria. These bacteria proliferate in an
environment filled with sick people who have poor immune systems and where antibiotics have eliminated
competing bacteria that are not resistant.
Bacteria that are resistant to modern antibiotics have even been found in the frozen bodies of people who
died long before those antibiotics were discovered or synthesized.1
History of Antibiotic Resistance
Antibiotics were first discovered through a providential experiment by Alexander Fleming in 1928. His
work eventually led to the large-scale production of penicillin from the mold Penicillium notatum in the
1940s. As early as the late 1940s resistant strains of bacteria began to appear. 2Currently, it is estimated
that more than 70% of the bacteria that cause hospital-acquired infections are resistant to at least one of
the antibiotics used to treat them.3
Antibiotic resistance continues to expand for a multitude of reasons, including over-prescription of
antibiotics by physicians, non-completion of prescribed antibiotic treatments by patients, use of antibiotics
in animals as growth enhancers (primarily by the food industry), increased international travel, and poor
hospital hygiene.2
How Do Bacteria Become Resistant?
Bacteria can gain resistance through two primary ways:
1. By mutation, and
2. By using a built-in design feature to swap DNA (called horizontal gene transfer)—bacteria share
resistance genes.
An antibiotic kills a bacterial cell by simply disrupting a critical function. This is achieved in the cell in
much the same way that a saboteur can cause a massive jetliner to crash by simply cutting the hydraulic
lines.
Antibiotic resistance of bacteria only leads to a loss of functional systems. Evolution requires a gain of
functional systems for bacteria to evolve into man.
The antibiotic binds to a protein so that the protein cannot function properly. The normal protein is usually
involved in copying the DNA, making proteins, or making the bacterial cell wall—all important functions for
the bacteria to grow and reproduce.
If the bacteria have a mutation in the DNA which codes for one of those proteins, the antibiotic cannot
bind to the altered protein; and the mutant bacteria survive. In the presence of antibiotics, the process of
natural selection will occur, favoring the survival and reproduction of the mutant bacteria. (The mutant
bacteria are better able to survive in the presence of the antibiotic and will continue to cause illness in the
patient.)
Although the mutant bacteria can survive well in the hospital environment, the change has come at a cost.
The altered protein is less efficient in performing its normal function, making the bacteria less fit in an
environment without antibiotics. Typically, the non-mutant bacteria are better able to compete for
resources and reproduce faster than the mutant form.
Let’s look at a famous example to help clarify this. During the anthrax scare shortly after the September
11, 2001, attacks in the U.S., Ciprofloxacin (Cipro) was given to potential victims. Cipro belongs to a
family of antibiotics known as quinolones, which bind to a bacterial protein called gyrase, decreasing the
ability of the bacteria to reproduce. This allows the body’s natural immune defenses to overtake the
infectious bacteria as they are reproducing at a slower rate. Quinolone-resistant bacteria have mutations
in the genes encoding the gyrase protein. The mutant bacteria survive because the Cipro cannot bind to
the altered gyrase.
This comes at a cost as quinolone-resistant bacteria reproduce more slowly.4, 5, 6 Resistance to this family
of antibiotics is becoming a major problem with one type of bacteria which causes food poisoning. This
bacteria increased its resistance to quinolones 10-fold in just five years.7
Bacteria can also become antibiotic resistant by gaining mutated DNA from other bacteria. Unlike you and
me, bacteria can swap DNA. But this still is not an example of evolution in action. No new DNA is
generated (a requirement for molecules-to-man evolution), it is just moved around. It’s like taking money
from your left pocket and putting it into your right pocket—it doesn’t make you wealthier. This mechanism
of exchanging DNA is necessary for bacteria to survive in extreme or rapidly changing environments like a
hospital (or like those found shortly after the Flood).8
What Does It Really Prove?
The mechanisms of mutation and natural selection aid bacteria populations in becoming resistant to
antibiotics. However, mutation and natural selection also result in bacteria with defective proteins that
have lost their normal functions.
Evolution requires a gain of functional systems for bacteria to evolve into man—functioning arms,
eyeballs, and a brain, to name a few.
Mutation and natural selection, thought to be the driving forces of evolution, only lead to a loss of
functional systems. Therefore, antibiotic resistance of bacteria is not an example of evolution in action but
rather variation within a bacterial kind. It is also a testimony to the wonderful design God gave bacteria,
master adapters and survivors in a sin-cursed world.