Evolution and Antibiotics Resistance

Before the dawn of antibiotics, evolution in bacteria has presented a challenge to society. Scientists have found that gene duplication and amplification (GDA), horizontal gene transfer (HGT) and mutation are significant mechanisms that bacteria utilize in order to become resistant to the presences of antibiotics. This discovery has also given scientist the knowledge to understand why and how bacteria evolve into resistant strands of bacteria. Bacteria can also reduce growth rate or toxicity (fitness costs) when not in the presence of a toxic drug in order to build resistance. These mechanisms for both external and internal situations are very important to the survival of bacteria.

Bacteria, when faced with toxic drugs like antibiotics, use different mechanisms in order to adapt and survive. Mutation and horizontal gene transfer (HGT) degrade the antibiotic and prevent the antibiotic from targeting the intended molecule. Mutation and HGT also have the ability to pump out targeting molecules from toxic drugs. GDA has been shown to facilitate antibiotic resistance by first duplicating and creating an over population of the bacteria, deletion of certain genes, and then amplifying certain genes thus making the bacteria more tolerant to antibiotics. During the studies of GDA, scientists have found that it is very unstable form of mutation. Scientists classify GDA as unstable because they have found it to be a difficult to study in a clinical isolation setting. In GDA gene amplification is very rapid, and often goes undetected. Scientists think that antibiotic treatment failures are the result of the rapid gene amplifications that are found in GDA.

When not faced with the threat of toxic drugs, scientists have identified a way that bacteria can increase antibiotic resistance by reducing fitness costs. Scientists identify fitness costs of bacteria that are building resistance towards toxic drugs by a reduction in growth rate and/or the toxicity of the bacteria. During the reduction of growth and toxicity, mutations occur that compensate for the reductions made in the growth rate and toxicity. These compensating mutation result in bacteria with higher resistance to antibiotics and although the growth rate and toxicity may not return fully, scientists found that growth rate and toxicity returns to about 10 percent below its previous growth and toxicity rates. Through this finding scientists have found that bacteria have been building resistance for centuries because it not only evolves from an external factor such as antibiotics but also an internal factors as well.

Bacteria have been in existence for centuries and throughout time, bacterium has used different mechanisms for different situations in order to evolve, and survive. Bacteria uses a mechanism, GDA, is what it uses when confronted with a toxic drug like antibiotics, while also using natural, unstressed evolution mechanism like mutation during the reduction of fitness