Bacteria can acquire antibiotic resistance through mutations in their DNA. These mutations can then spread rapidly through bacterial populations by binary fission and conjugation. There are certain measures that can be implemented to reduce to spread of antibiotic-resistant bacteria, however, they all come with their own issues.
Resistance
There are two types of resistance: primary and secondary. Primary resistance is when a bacteria is naturally resistant to an antibiotic. Secondary resistance is resistance that is acquired: these bacteria were originally susceptible to the antibiotic but now these antibiotics are ineffective.
Secondary resistance
Bacteria develop antibiotic resistance through three main biochemical mechanisms:
1.
A decrease in uptake or an increase in expulsion of the antibiotic.
2.
Production of enzymes that can modify or inactivate the antibiotic.
3.
Development of a new biochemical pathway that means that pathway that was targeted by the antibiotic is now redundant.
Bacteria are prone to errors during DNA replication at a rate of 1 in 106 base pairs. These gene mutations produce different alleles of a gene and a change in a single gene is enough to allow resistance.
Example
Resistance to sulfonamide antibiotics is controlled by a single gene that encodes a synthase enzyme.
Horizontal gene transfer
Vertical gene transfer is when a bacterium replicates its own DNA and passes the copies to its daughter cells. However, bacteria are able to pass DNA, either as a plasmid or part of their nucleoid, to another cell in a process called conjugation. This is a type of horizontal gene transfer. This is how antibiotic resistance can spread quickly through a population of bacterial species and accounts for the increase in multiple-antibiotic-resistant bacteria.
A.
Plasmid conjugation
B.
Conjugation by transfer of a copy of part of the chromosome
1.
Plasmid
2.
Conjugation tube
3.
Copy of plasmid DNA
4.
Remainder of DNA of the new plasmid
5.
New plasmid
6.
Copy of part of nucleoid DNA
7.
Nucleoid DNA
8.
Double-stranded DNA assembled and inserted into new chromosome
9.
Conjugation tube closes
i.
A conjugation tube is formed between the two bacteria.
ii.
A copy of plasmid DNA or nucleoid DNA is passed through the conjugation tube.
iii.
The remainder of DNA of the new plasmid is formed and the plasmid is assembled or the double-stranded DNA is assembled and inserted into the circular chromosome.
iv.
The conjugation tube is closed.
Measures to reduce antibiotic use
To control the spread of antibiotic resistance there are certain measures that should be implemented.
Measure
Explanation
Problems
Preventing farmers from adding antibiotics to animal feeds
When antibiotics are added to animals feeds, they are often used at subclinical concentrations. This doesn't kill the bacteria and instead creates a selection pressure that favours antibiotic resistance.
Agricultural groups would strongly oppose this rule as it may reduce profits and the quality of their products.
Restricting antibiotic prescriptions administered by doctors
This would reduce the selection pressure favouring bacteria with resistance.
Many patients may be unwilling to accept no prescription. This puts pressure on doctors.
Patients must complete their full course of antibiotics
Some people do not complete the full course of antibiotics because they start to feel better. This means not all of the bacteria will be destroyed and a selection pressure favouring resistant bacteria will be created.
This measure relies on people following this advice. It is unlikely that everyone will.
Create new antibiotics
This involves making new antibiotics faster than bacteria can acquire resistance to them.
Development of antibiotics takes many years and drug trials are a large component of that. Often the development is unsuccessful and can be very expensive. Many pharmaceutical companies will not want to invest money in antibiotic production as it is very risky and probably won't make any profits.
Hospitals
In the UK, infections from multi-drug resistant bacteria are mainly in hospitals or community care home settings. There are measures that can be taken to reduce the spread of these infections.
Measure
Explanation
Problems
Isolated infected individuals
This reduces the risk of transmission between infected and vulnerable patients.
Many hospitals have bed shortages and therefore isolation rooms are not available.
Hand-washing by staff and visitors
Effective hand-washing with soap removes bacteria from the skin so it cannot be transmitted by contact. This is a cheap and easy way to reduce disease spread.
Hospitals may struggle to enforce this rule as thousands of people enter every day.
Staff wearing personal protective equipment (PPE)
Staff should wear gloves and aprons when handling a patient and then dispose of them immediately after.
This may reduce the time a member of staff spends with a patient because they need to remove and dispose of equipment. In an emergency, there might not be enough time to put on PPE. During pandemics/epidemics there may be a shortage of PPE and this could lead to it becoming expensive.
Screening patients when they arrive for "superbug" infections
This allows infected individuals to be isolated so the infection does not spread further.
This costs money and could be time-consuming.
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Evolution by natural selection
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Antibiotic resistance: causes and prevention
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FAQs - Frequently Asked Questions
What is horizontal gene transfer?
Horizontal gene transfer is when bacteria are able to pass DNA, either as a plasmid or part of their nucleoid, to another cell.
What is secondary resistance?
Secondary resistance is resistance that is acquired, these bacteria were originally susceptible to the antibiotic but now these antibiotics are ineffective.
What is primary resistance?
Primary resistance is when a bacteria is naturally resistant to an antibiotic.
