What is antimicrobial resistance?

Part 2: How do researchers measure antibiotic resistance and where did it come from? These are some of the insights gained at a conference on antimicrobial resistance.

Recent talk about antimicrobial resistance must mean that this is something new, right? That was my assumption when I represented Michigan State University Extension at a recent National Institute of Animal Agriculture (NIAA) conference dedicated to antimicrobial resistance. But actually antimicrobial resistance has been around maybe as long as microbes themselves. In this second part of a four-part series on antimicrobial resistance, we look at the definition of antimicrobial resistance.

Many antibiotics are naturally produced by bacteria or fungi. One notable example is the development of penicillin from a mold that was found to inhibit bacterial growth. There are some bacteria intrinsically resistant to antibiotics. Bacteria initially may acquire resistance through mutations in genes that are then passed on as the organism replicates.

Several presenters at the NIAA conference on antimicrobial resistance cited studies in which genes conferring antimicrobial resistance were found in certain isolated places that had had no human contact. It occurred naturally and not as a result of human intervention.

While intrinsic resistance enables bacterial populations to grow in the presence of an antibiotic, of greater interest to scientists is resistance that is acquired by bacteria. Resistance can spread rapidly through gene acquisition by horizontal gene transfer. This type of development of resistance not only increases the pace of the development of resistance, but also enables bacteria to develop resistance to multiple antimicrobials even without being exposed to them.

Determining where and why resistance develops and spreads is important in order to be able to reduce the level of antimicrobial resistance. Within the food production system, there are many opportunities for spread of resistance. For instance, if we measure resistance genes in yogurt did it come from the milk produced by cows to make yogurt, or some other part of the yogurt manufacturing process?

Likewise, if we measure resistance genes in bacteria from water downstream from a farm, did it come from the farm or some other source that contributes biomaterial to the stream? Research into these and others systems has shown that what may seem to be the most likely source of antimicrobial resistance may not indeed be the case.

Measuring the genes that cause resistance is not the end of research. The development of resistance is a much more difficult question to answer, but critical to the success of reducing resistance.

Because antimicrobial resistance occurs naturally, we will never eliminate it. However, since it also occurs through human actions as well, whether in animal agriculture or medical practice, we need to work to control the growth of antimicrobial resistance. To do that, we have to focus on our mutual interests of improved health.

Related articles:

Antibiotic resistant bacteria issue demands action (Part 1)

Where does antimicrobial resistance come from? (Part 3)

Moving forward with antimicrobial resistance (Part 4)


Phil Durst

Phil Durst
9 articles

Oscoda County Extension Director, NE Michigan Extension Dairy Agent

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