Genetic changes in pathogens

The time it takes for a species to reproduce determines how long it takes for inherited changes to affect a species’ gene pool.

A shorter generation time results in faster inherited changes, as the time frame between successive generations is reduced.

In the bacteria Escherichia coli (E. coli), a generation time of only 20 minutes can result in a significant change in its gene pool in a short time frame.

Viruses also have a rapid reproduction rate, varying depending on the type of virus and the host cell they infect. Rapid replication contributes to a high mutation rate, which can result in increased genetic variation within viral populations.

Use this page to revise the following concepts within genetic changes in pathogens:

Bacterial resistance

Bacterial resistance is a natural process in which bacteria evolve to survive and grow in the presence of drugs designed to kill them, increasing the risk of disease spread and severe illness.

The diagram below gives an overview of how antibiotic resistance can occur.

A diagram explaining how antibiotic resistance occurs. In Stage 1 there are groups of bacteria, and a few of them have resistance to antibiotics. In Stage 2 antibiotics kill most germs and pathogens, but some survive. In Stage 3, these surviving bacteria are now antibiotic resistant and can develop freely. Finally, in Stage 4, this resistance is transferred to other bacteria, resulting in increasing antibiotic resistance

Antibiotic resistance is naturally occurring in bacterial populations, however human activity, such as the misuse and overuse of antibiotics, accelerates the emergence and spread of bacterial resistance.

To prevent antibiotic resistance, people should implement personal hygiene strategies to limit the spread of bacterial diseases. Additionally, the over-prescription of antibiotics should be avoided, though when prescribed, a complete course of treatment should be followed.

Antigenic shift and Antigenic drift in viruses

Antigenic shift is a process where two or more different strains of a virus combine to create a new subtype of virus. Often, this new viral strain will have a unique combination of surface antigens, different from the original strains. Antigenic shift occurs when a host cell is infected by more than one strain of similar viruses at the same time, and their genetic material is spontaneously combined.

This is often the mechanism responsible for a virus from an animal population gaining the ability to infect humans.

Antigenic shift is rare but sudden and results in significant genetic alteration that can lead to new viral strains quickly. Flu pandemics are a notable example of antigenic shift, as is the emergence of COVID-19 in early 2020.

Antigenic drift is a viral process where small gene mutations cause changes in viral antigens due to random copying errors during replication, to create a new strain of virus. Although a slower process than antigenic shift, the rapid generation rates of virus means this can still regularly create new variants of a virus that may be unknown to a previously exposed immune system.

This diagram illustrates the difference between the two mechanisms by which viruses evolve to change their surface proteins.

An image demonstrating the processes of antigenic shift and drift. Antigenic shift involves Virus A and Virus B combining in a host cell, and intermixing RNA. This produces Virus C. In antigenic drift Virus A accumulates mutations over time, leading to Virus B.