AMR in the environment: extended learning
Calculating exposure in practice
Activity: Calculating exposure in practice
Let’s use ESBL-producing E. coli bacteria in water used for bathing as an example.
ESBL-producing E. coli is an Escherichia coli bacterium that produces Extended Spectrum Beta Lactamases (ESBLs), a group of enzymes capable of breaking down a broad spectrum of antibiotics, particularly penicillin and specific cephalosporins. ESBL-producing E. coli are very common in some countries, can be transmitted via water and can lead to difficult to treat urinary tract or other infections.
Imagine swimming in surface water contaminated with ESBL-producing E. coli. For one episode of recreational swimming, people are assumed to ingest some 30–50 ml of water. Supposing that the concentration of ESBL-producing E. coli was 2 CFU/L, what would the ingested dose of ESBL-producing E. coli be per year for someone swimming daily throughout the year?
Answer
The answer is up to 36 ESBL-producing E. coli per year.
Using the equation: D = c × V = 2 ESBL-producing E. coli per litre × 0.05 litre = 0.1 ESBL/day or 36 ESBL-producing E. coli per year if swimming daily throughout the year.
- D = c × V
- D = 2 ESBL-producing E. coli per litre × 0.05 litre
- D = 0.1 ESBL per day or 36 ESBL-producing E. coli per year if swimming daily throughout the year.
where:
- D = dose
- c = concentration of resistant bacterium/ARG in the compartment
- V = volume ingested or inhaled per time unit
Now that you understand the way to calculate the ingested dose, you can apply it to some real-world examples.
Thinking about your own lifestyle, try to estimate the quantity of water that you would ingest through bathing in surface water per year. Does this quantity differ much from the intake of other members of your family, or specific groups in your country? If so, suggest why this might be the case.
Discussion
Personal exposure can vary greatly depending on lifestyle. For example, if members of your family don’t swim at all, their exposure through this route could be negligible; that might be very different for smaller children who engage in water play, or in situations where suitable bathing water is nearby and used regularly. It can be difficult to capture such differences through a generic exposure assessment.
When you’ve tried this activity you should return to Section 3.1 of the course [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] .
