4.1.16 Antibiotics Flashcards
Describe the use of antibiotics.
When humans experience a pathogenic bacterial infection they are often prescribed antibiotics by a healthcare professional
Antibiotics are chemical substances that inhibit or kill bacterial cells with little or no harm to human tissue
Many antibiotics are derived from naturally occurring substances that are harmful to prokaryotic cells (structurally or physiologically) but usually do not affect eukaryotic cells
The aim of antibiotic use is to aid the body’s immune system with fighting a bacterial infection
Penicillin is a well-known example; it was the first antibiotic to be discovered in 1928 by Sir Alexander Fleming
Antibiotics are either described as being bactericidal (they kill) or bacteriostatic (they inhibit growth processes), they target prokaryotic features but can affect both pathogenic and mutualistic bacteria living on or in the body
Some antibiotics are derived from fungi while others are synthetic or semi-synthetic
Broad-spectrum antibiotics act on a wide range of bacteria while narrow-spectrum antibiotics act on a very small number of bacteria
Doctors often prescribe broad-spectrum antibiotics (e.g. Amoxicillin) unless a culture has been taken to prove the need for a narrow-spectrum antibiotic
In all species, there exists genetic diversity within populations, and the same applies to disease-causing bacteria
Individual bacterial cells may possess alleles that confer resistance to the effects of the antibiotic
These alleles are generated through random mutation and are not caused by antibiotic use, but antibiotic use exerts selection pressures that can result in an increase in their frequency
Bacteria have a single loop of DNA with only one copy of each gene so when a new allele arises it is immediately displayed in the phenotype
When an antibiotic is present:
Individuals with the allele for antibiotic resistance have a massive selective advantage so they are more likely to survive, reproduce and pass genome (including resistance alleles)
Those without alleles are less likely to die and reproduce
Over several generations, the entire population of bacteria may be antibiotic-resistant
Antibiotic resistance is an important example of natural selection
Some pathogenic bacteria have become resistant to penicillin as they have acquired genes that code for the production of the enzyme β-lactamase (also known as penicillinase), which breaks down penicillin
What are the consequences of antibiotic resistance?
Commonly prescribed antibiotics are becoming less effective for many reasons, the main being:
Overuse of antibiotics and antibiotics being prescribed when not necessary
Large scale use of antibiotics in farming to prevent disease when livestock are kept in close quarters, even when animals are not sick
Patients failing to complete the full course of antibiotics prescribed by doctors
These factors have led to a reduction in the effectiveness of antibiotics, and an increase in the incidence of antibiotic resistance
Bacteria living where there is widespread use of many different antibiotics may have plasmids containing resistance genes for several different antibiotics, giving them multiple resistance and presenting a significant problem for doctors
In addition, resistance may first appear in a non-pathogenic bacterium, but then be passed on to a pathogenic species by horizontal transmission
There is a constant race to find new antibiotics as resistant strains are continuously evolving
How can antibiotic resistance and its impact be reduced?
Ways to prevent the incidence of antibiotic resistance increasing include:
Tighter controls in countries in which antibiotics are sold without a doctor’s prescription
Doctors avoiding the overuse of antibiotics, prescribing them only when needed (patients must only be given antibiotics when absolutely essential) – doctors should test the bacteria first to make sure that they prescribe the correct antibiotic
Antibiotics not being used in non-serious infections that the immune system will ‘clear up’ (patients must not keep unused antibiotics for self-medication of such non-serious infections in the future)
When prescribed a course of antibiotics, the patient finishing the entire course (even if they feel better after a few days) so that all the bacteria are killed, and none are left to mutate to become resistant strains
Antibiotics not being used for viral infections (antibiotics have no effect on viruses anyway, and this just provides an unnecessary chance for bacteria to develop resistance)
The use of ‘wide-spectrum’ antibiotics being reduced and instead those antibiotics that are highly specific to the infection (‘narrow-spectrum’ antibiotics) being used
The type of antibiotics prescribed being changed so that the same antibiotic is not always prescribed for the same infections and diseases (this reduces the chance of a resistant strain developing)
The use of antibiotics being reduced and more tightly controlled in industries such as agriculture – controls are now in place to limit their use in farming, where antibiotics are used to prevent, rather than cure, bacterial infections
The spread of already-resistant strains can be limited by:
Ensuring good hygiene practices such as handwashing and the use of hand sanitisers (this has reduced the rates of resistant strains of bacteria, such as MRSA, in hospitals)
Isolating infected patients to prevent the spread of resistant strains, in particular in surgical wards where MRSA can infect surgical wounds
