4.2 Spread of resistance in bacteria and the environment

Earlier in this module you learned that bacteria are all around us. Some types of bacteria are common to all living beings (humans, animals and plants). Remember from Section 2.1 how fast bacteria replicate?

Consider a few Salmonella bacteria that have infected a chicken. The chicken is treated with antibiotics, and one of the bacteria happens to be resistant to the antibiotic that is given. All the other bacteria will be killed by the antibiotic, but the resistant bacterium will survive, divide, multiply and pass the resistance to all offspring. In addition, bacteria can pass on resistance between each other by other mechanisms called horizontal transfer, which is explained in the module Introducing antibiotic resistance.

Activity 17: Spread of antibiotics in the environment

Study Figure 6 (from Berkner et al., 2014) on the different ways that antibiotics spread in the environment and answer the question that follows. Just as antibiotics can spread in the environment, so can some resistant bacteria.

Figure 6 The pathway of the spread of antibiotics in the environment.

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This figure shows the pathway of the spread of antibiotics in the environment. Starting with the application of antibiotic agents (red dots) in human and veterinary medicine in the upper left corner, the spreading of antibiotic residues in the ecosystem is drawn as a web of exposure pathways.

Figure 6 The pathway of the spread of antibiotics in the environment.

Identify three ways that antibiotics can end up in the groundwater.

Discussion

Three ways that antibiotics can end up in the groundwater are through:

• waste deposits from humans that contain antibiotic-resistant bacteria
• run-off from fields that have been fertilised with manure that carries antibiotic-resistant bacteria, or with sewage sludge from the sewage plant that carries antibiotic-resistant bacteria
• excrement or droppings from animals that carry antibiotic-resistant bacteria.