Antibiotics are a very important part of current medical treatment, but science is discovering the overuse can have unintended consequences that can impact gut health.
Antibiotics have saved millions of lives by reducing or removing pathogenic bacteria. However, we are now learning that overuse of antibiotics can have the unintended consequence of also reducing or removing resident bacteria that are important for gut health, as well as increasing the abundance of antibacterial resistance genes.
Antibiotic effects on the gut microbiome
Antibiotics come in many different forms. Some can target a wide range of bacteria (broad-spectrum) while others will target only a few types of bacteria (narrow-spectrum). Broad-spectrum antibiotics are the most commonly prescribed because often the microorganism causing an infection is unknown. Use of broad-spectrum antibiotics have been observed to have several impacts on gut health, including:
- reducing microbial diversity in the gut1–5
- reducing protective species such as Bifidobacterium spp.1,2,6
- promoting the colonisation of opportunistic pathogens such as Clostridium difficile that can cause antibiotic-associated diarrhea7–9
In infants and young children, antibiotic use has also been linked to an increased risk of asthma and weight gain1,10.
In a healthy gut microbiome, the resident microorganisms help protect against invasion by opportunistic pathogens through a process called colonisation resistance. This involves different methods to inhibit pathogens, such as:
- producing anti-microbial compounds
- outcompeting pathogens for space in the gut
- maintaining the mucus layer so pathogens cannot reach intestinal cells
- training the immune system to respond to pathogens11,12
When the resident gut microorganisms are reduced during antibiotic use, these protective functions may stop occurring and provide an opportunity for pathogenic bacteria to colonise.
Recovery of the gut microbiome
After an antibiotic course, recovery of the gut microbiome can take some time. In general, after short-term antibiotic use (between five and ten days), studies have observed it can take at least one to two months for most bacterial groups to recover to pre-antibiotic levels2,3,13–16. However, these studies have also shown that even after two to four years, some bacterial groups do not recover completely and antibacterial resistance genes can also persist at increased levels for at least one to two years following antibiotic use13,14,16,17. Therefore, even a short course of antibiotics can have long-term effects on the gut microbiome.
Improving gut health after antibiotics
There is increasing clinical evidence that taking probiotics during and after antibiotic use can decrease the risk of invasion by opportunistic pathogens and development of antibiotic-associated diarrhea18–20. However, further research is still needed in this area and it is likely that different strains of probiotics have different levels of efficacy.
Although it is likely probiotics can protect against the invasion of opportunistic pathogens, a recent small study observed that probiotics may also inhibit the return of the native gut microbiota21. The study found it took longer for the native gut microbiota to return in individuals who consumed probiotics for 28 days following antibiotic use compared to individuals who did not take probiotics. Therefore, it appears there are both positive and negative factors to consider when deciding to take probiotics to help the gut microbiome recover from antibiotics.
A good general strategy to improve gut health is to make sure you feed your gut microbiome foods that will allow your beneficial resident microbiota to grow back. This means eating a wide variety of foods that are high in fibre and plant polyphenols such as fruits, vegetables, legumes, nuts and whole grains22.
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Intestinal microbiome is related to lifetime antibiotic use in Finnish pre-school children.
Nature communications, 7, 10410 (2016). Doi: 10.1038/ncomms10410
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Determining the long-term effect of antibiotic administration on the human normal intestinal microbiota using culture and pyrosequencing methods.
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Short-term effect of antibiotics on human gut microbiota.
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The initial state of the human gut microbiome determines its reshaping by antibiotics.
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Short-term antibiotic treatment has differing long-term impacts on the human throat and gut microbiome.
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