2 How antibiotic resistance spreads

In Week 4, you learned that, in the presence of antibiotics, resistant bacteria have a survival advantage over sensitive bacteria and can quickly dominate a bacterial population. Resistance is an inevitable consequence of using antibiotics. The more that antibiotics are used, the more widespread resistance becomes.

You have also learned that antibiotic resistance spreads in a bacterial population by resistance genes passing from one bacterium to another. In Activity 2, you will discover that antibiotic resistance also spreads when resistant bacteria move from one human or animal host to another.

Activity 2 How does antibiotic resistance spread?

Timing: Allow about 10 minutes

First, watch the video below which shows how antibiotic resistance spreads in different communities.

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Transcript: Video 2 How does antibiotic resistance spread?

INSTRUCTOR:

How does antibiotic resistance spread? Antibiotic resistance is the ability of a bacteria to combat the action of one or more antibiotics. Humans and animals do not become resistant to antibiotic treatments, but bacteria carried by humans and animals can.

In animal farming, animals may be treated with antibiotics, and they can therefore carry antibiotic-resistant bacteria. Vegetables may also be contaminated with antibiotic-resistant bacteria from animal manure used as fertiliser. Finally, antibiotic-resistant bacteria can spread to humans through food and direct contact with animals.

In a community, humans sometimes receive antibiotics prescribed to treat infections. However, bacteria develop resistance to antibiotics as a natural adaptive reaction, and then antibiotic-resistant bacteria can spread from the treated patient to other persons. In health care facilities, humans may receive antibiotics and then carry antibiotic-resistant bacteria. These can spread to other patients via unclean hands or contaminated objects.

Patients who may be carrying antibiotic-resistant bacteria will ultimately be sent home and can spread these resistant bacteria to other persons. Travellers requiring hospital care while visiting a country with a high prevalence of antibiotic resistance may return home with antibiotic-resistant bacteria. Even if not in contact with health care, travellers may carry and import resistant bacteria acquired from food or the environment during travel.

Bacteria have become resistant because antibiotics have been used for the wrong reasons or incorrectly in different settings. Infections with resistant bacteria are difficult to treat.

End transcript: Video 2 How does antibiotic resistance spread?

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Video 2 How does antibiotic resistance spread?

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Now, answer the following questions:

1. In which ways can people be infected by antibiotic-resistant bacteria?

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2. What roles do people moving from one geographical region to another play in spreading antibiotic resistance?

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Answer

1. Antibiotic-resistant bacteria can spread to humans through food and through direct contact with animals or other people (for example, via unclean hands or contaminated objects). Resistance may also develop naturally if a person takes antibiotics to treat a bacterial infection. You will learn more about how infections are spread between people in Week 7.

2. The numbers of people travelling abroad for work or holidays is rising. This increases the likelihood that resistant bacteria, acquired from food or the environment, will be brought home and spread to other people.

Antibiotics eventually end up in the environment. Contaminated soil and waterways become reservoirs of antibiotics and antibiotic-resistant bacteria. This creates selective pressure that encourage the development and spread of resistance and the transfer of antibiotic-resistant bacteria to people and animals (Figure 1).

Figure 1 Main antibiotic routes into the soil and waterways. 1. Uptake of resistant bacteria in the food chain 2. Excreted antibiotics and their metabolites enter the sewage system 3. Water treatment facilities are not completely effective at removing bacteria which then enter waterways 4. Animal waste containing resistant bacteria and unmetabolised antibiotics contaminates soil and water directly and also used to fertilise crops 5. Antibiotics in crop sprays contaminate soil and waterways directly 6. Pharmaceutical waste containing antibiotics may be released directly into the environment.

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Main antibiotic routes into the soil and waterways. 1 Uptake of resistant bacteria in the food chain. 2 Excreted antibiotics and their metabolites enter the sewage system. 3 Water treatment facilities are not completely effective at removing bacteria which then enter waterways. 4 Animal waste, containing resistant bacteria and unmetabolised antibiotics, contaminates soil and water directly and is also used to fertilise crops. 5 Antibiotics in crop sprays contaminate soil and waterways directly. 6 Pharmaceutical waste containing antibiotics may be released directly into the environment.

Figure 1 Main antibiotic routes into the soil and waterways. 1. Uptake of resistant bacteria in the food chain 2. Excreted antibiotics ...

Two interrelated factors contribute to the spread of antibiotic resistance. An increased rate of resistance, which results in higher numbers of antibiotic-resistant bacteria, and a greater number of cases of infectious diseases. Both factors increase the use of antibiotics which, in turn, drives the antibiotic resistance rate.

In the following sections, you will look at the main drivers of antibiotic resistance:

• poor hygiene and infection control
• the overuse of antibiotics
• the misuse of antibiotics.

You will also consider how the lack of new antibiotics and gaps in global infection and resistance data exacerbate the problem.