Case Study Zani ZartashahBiology 21-10-2015

The Evolution of Antibiotic Resistance in Bacteria

1. Did the rifampin-resistant bacteria found in the autopsy evolve within the patient’s lungs or did they result from a brand new infection? Explain the evidence.

The rifampin-resistant bacteria found in the autopsy evolved within the patient’s lung. When the patient was treated with rifampin they initially responded well because the bacteria culture was sensitive to the antibiotic. Soon after when they relapsed, the outcome was not the same. The bacteria culture was not sensitive to the antibiotic like it had been previously and invaded the lungs again in large numbers. When comparing the new bacteria culture to the original it was seen that DNA sequencing was identical except for a single mutation. This single base-pair mutation was known to confer resistance to the antibiotic. Since the bacteria in the patient had been exposed to a new environmental selective agent when rifampin was administered, it gave the mutant strain a major adaptive advantage. This proves that the bacteria had evolved (mutated) through the adaptive advantage of the mutant strain and was not a result of a brand new infection.

2. Most antibiotics are derived from microorganisms that do not occur naturally in the human body. Most infectious bacteria showed no resistance to these antibiotics when they were first used in the 1940’s, because pathogens (disease causing organisms) did not already have antibiotic resistance to them. Why?

These pathogens did not already have antibiotic resistance to them because the antibiotics were not previously introduced before, therefore they could not adapt and mutate. The 1940’s was the Golden Age of antibiotics discovery. They were very effective because bacteria showed no resistance to them. As time has gone by the effectiveness of these antibiotics has decreased. Since bacteria have a rapid reproduction rate, this advantage allows adaptation to occur quickly. The more of the same antibiotics we take, the DNA sequencing of the bacteria’s genes will show a mutation which is known to resist the antibiotic.

3. Bacteria that are sensitive to antibiotics usually out-compete resistant strains in the absence of antibiotics. Account for this observation

Bacteria that are sensitive to antibiotics usually out-compete resistance strains in the absence of antibiotics. This is because many traits that provide antibiotic resistance are harmful to the bacteria and there is a cost for resistance. For example a strain of E. coli bacteria possess a plasmid with a gene that enables it to produce an enzyme. This enzyme gives the bacterium resistance to the antibiotic ampicillin. To maintain the antibiotic resistance, the bacterium must devote cellular resources to producing the enzyme. As a result of these costs of resistance it is a

Case Study Zani ZartashahBiology 21-10-2015disadvantage being an extra thing for the cell to do. Thus, when an antibiotic is not present, natural selection often favours those bacteria that do not carry antibiotic-resistant alleles.

4. Tuberculosis patients are now routinely given two different antibiotics at the same time. Why might this approach be more effective than administering a different antibiotic only after bacteria develop resistance to the first?

Giving the patient two different antibiotics at the same time because is more effective and time efficient. If the bacteria has an antibiotic resistance to one antibiotic it is very unlikely it will have resistance to the other and has another mutation. This method is also more time efficient. It would take longer to have the patient try out two antibiotics at the same time than try one and then become sicker only to then try a different one. Giving the patient two antibiotics instead of one results in faster relief and effectiveness.

5. Suggest some strategies that could help reduce the incidence of antibiotic resistance in your own home, your school and in society at large.

Home:

Use antibiotics only when a doctor prescribes them When a doctor prescribes you antibiotics, take it as directed and the full prescription or

further problems may arise When buying meat, try choosing antibiotic free meats Take care of your body – sleep well, eat well and keep hydrated

School:

Proper hygiene can prevent infections – washing hands Bringing a little bottle of hand sanitizer removes many germs Do not share straws and drinks with other sick people or people in genera.

1 mL saliva = 100 million bacteria

Society:

Becoming more educated in the topic of antibiotic resistance can help reduce the chances of getting sick

Do not use antibiotics to treat viral infections such as a common cold Never share antibiotics and never use leftover prescriptions