3.2 Consequences of resistance

Discussion

Treatment of infectious diseases caused by bacteria

Antibiotics are the ‘magic bullets’ that can attack bacterial infections without killing the patients. That does not mean that the antibiotic treatment is completely harmless to the patients: antibiotics disrupt the normal bacterial flora as they not only kill the pathogenic organism, they also kill the normal flora (good bacteria). So antibiotics must be used carefully, only where appropriate, and should not be prescribed indiscriminately. For example, for a mild sore throat with no signs of fever, the infection is likely to be caused by a virus. Warm saline gargles may be effective at relieving symptoms, while antibiotics may have no effect at all. Similarly, in animals, small wounds can be managed with proper wound dressings and care without the need to prescribe antibiotics.

You have also learned that there are different classes of antibiotics that work in different ways. So if a bacterium becomes resistant to one kind of antibiotic, there might be another type of antibiotic with a different mechanism of action that is still effective against that bacterial infection. However, what happens if the bacteria become resistant to that one as well, and then to the next one and the next one? This is already happening with some bacteria, which we call multi-drug-resistant bacteria. If a strain of bacteria becomes resistant to the last class of antibiotics that is available to treat it, we have no way to treat the infections that it causes. Methicillin-resistant Staphylococcus aureus (MRSA) is an example of such a multi-drug-resistant bacterium.

Surgery

Without effective antibiotics, surgery will become riskier because there will be no way to treat bacterial infections that might happen as a complication of surgery. To prevent the risk of infection, surgery should be performed in aseptic conditions. However, there is still a possibility that bacteria on patients’ skin may enter the body during the course of surgery. In Section 2.1 you saw that under the right conditions, bacteria can replicate very quickly. Without antibiotics to treat the infection, the risk of complications from the surgery is high.

Crop production

Bacteria and fungi cause significant plant disease and production losses worldwide. We need antibiotics to treat crop diseases caused by bacterial pathogens to preserve food security and livelihoods. Intensive agriculture often involves monocultures of crops in which pathogens can spread easily. In a plot of land where plants are widely spaced, plant diseases cannot spread as easily. The reality is that we are growing our crops in conditions that favour spread of pathogens, so we need to be able to continue to treat the diseases they cause.

Meat production

Antimicrobials are used to treat infections in food-producing animals. Just like humans, food-producing animals can be infected with bacterial pathogens. Because of the pressure placed by human population growth on agricultural systems, food-producing animals are often housed very close together in what’s referred to as intensive farming systems. When animals are housed close together, bacterial infections occur more frequently and spread more readily. Improving biosecurity in intensive farming systems can reduce the incidence of bacterial diseases but many of these farming systems may still require antimicrobials to control disease at some point so that animals do not suffer, and farms remain economically viable.

A good example is the use of antimicrobials to treat mastitis in high-producing dairy systems. In these systems, dairy cows are kept together in a large herd (possibly at high density), and milked at least twice daily using machines that attach to the cows’ teats. Milking with shared machinery and close proximity with other members of the herd can lead to infection of the mammary glands – mastitis, which is painful and reduces milk quality and safety.

There are many ways to reduce and control the incidence of mastitis on a dairy farm, such as making sure milking equipment is cleaned properly and that cows’ teats are cleaned before and after milking. Despite this, most high-producing commercial farms still need to treat mastitic cows with antimicrobials when necessary. If these antimicrobials become ineffective, treatment of cows with mastitis will also be less effective. This will likely lead to more euthanasia of infected cows and will impact the quality, quantity and expense of milk production.