Antibiotic Resistance Why Evolution is Important Now

What are Antibiotics? Chemicals that either kill or inhibit the growth of bacteria Naturally produced by bacteria and fungi Erythromycin – produced by bacteria Streptomyces erythraeus Penicillin – produced by fungi Penicillium Can be also artificially produced in the laboratory Sulfanilamide, Cipro – completely synthetic Ampicillin, Amoxycillin – natural products with chemical modification.

How Antibiotics Work Prevent proper formation of the bacterial cell wall Cell wall normally prevents cell from bursting when excess water enters the cell – if cell wall is damaged, cell bursts and dies Examples are penicillin, ampicillin, amoxycillin, vancomycin Disrupt protein synthesis or cell metabolism -Bind to ribosomes - disrupt process in various ways Examples are tetracycline, erythromycin, streptomycin, kanamycin -Block synthesis of needed metabolic chemicals – e.g. folic acid Example is sulfanilamide Interfere with DNA synthesis Block replication of the bacterial chromosome Example is Cipro

What Is Antibiotic Resistance? Antibiotic Resistance is when bacteria possess the ability to deactivate the action of antibiotics.

What are the Mechanisms of Antibiotic Resistance? Bacteria possess structures that prevent antibiotic from entering the cell (modify cell wall). Bacteria can pump antibiotic back out of the cell through their plasma membrane. Bacteria can destroy the antibiotic once inside the cell. Bacteria can bind other substances to the antibiotic once inside the cell in order to inactivate its action.

How is Antibiotic Resistance Acquired? MOST BACTERIA DO NOT NATURALLY POSSESS RESISTANCE TO ANTIBIOTICS!! (Other than their own that they produce – for example - Streptomycetes are resistant to Streptomycin)

Antibiotic Resistance is Acquired Through: Natural mutation Exchange of genes through: Conjugation Transduction Transformation

Conjugation Bacteria connect to each other using a thread-like structure called a pilus. A section of DNA – often a circular piece of DNA called a plasmid is transferred from one bacterium to the other. Illustrations from Doc Kaiser’s Microbiology Home Page http://student.ccbc.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/

Transduction A virus can take up a piece of DNA from its bacterial host and insert it into its own viral genome. It then takes over the bacterial cell host and replicates many copies of the virus. The bacterial cell is ruptured and the replicated viruses erupt from the infected cell. When one of the viruses infects a new cell, it inserts the original bacterial DNA into the new cell, where the stolen piece becomes integrated into the new cell's DNA. Illustrations from Doc Kaiser’s Microbiology Home Page http://student.ccbc.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/

Transformation DNA from dead bacteria is taken in and incorporated into the genome of living bacteria Illustrations from Doc Kaiser’s Microbiology Home Page http://student.ccbc.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/

So What’s the Big Deal if One or Two Bacteria Have Antibiotic Resistance? If the antibiotic resistance offers a competitive advantage to the bacteria, other bacteria will die off, and the resistant bacteria will thrive. Within that particular environment, rapid resistant bacterial reproduction would lead to the development of a resistant strain that could cause harm to humans and other living things.