Antibiotics can lead to fatal fungal infection

A new study by the University of Birmingham has revealed that fungal infections kill around the same number of people each year as tuberculosis. They mostly take hold in people who are vulnerable because they have a defective immune system caused by an underlying disease, such as cancer, or a viral infection, such as HIV or Covid.

The study shows that antibiotics can cause immune system defects that increase the risk of dangerous fungal infections. Candida is a fungus that is a common cause of fungal infections in humans. The yeast infection thrush is caused by Candida. But it can also cause a life-threatening bloodstream infection called invasive candidiasis. One of the risk factors for getting invasive candidiasis is antibiotics. When we take antibiotics, we kill off some of our gut bacteria. This can create space for gut fungi (like Candida) to grow. And if your intestines become damaged by chemotherapy or surgery, then the Candida can get out of the gut and cause a bloodstream infection. Yet the most common way people get invasive candidiasis is not from their gut, but from their skin.

Patients in the ICU who are fitted with an intravenous catheter can get invasive candidiasis, especially if they have been treated with antibiotics.

Researchers wanted to find out exactly why antibiotics make fungal infections such as invasive candidiasis more probable. To investigate, they treated mice with a broad-spectrum antibiotic cocktail and then infected them with Candida fungi. They compared them to a control group of mice that we infected with the Candida fungus, but didn't treat with the cocktail of antibiotics. The researchers found that antibiotic treatment made mice sicker when they were infected with the fungus.

In this fungal infection, it is normally the kidneys that become the target of the infection and mice get sick because their kidneys stop working. But that wasn't the case here.

Although antibiotics made the mice sicker, they were controlling the fungal infection in the kidneys just as well as the mice that hadn't received antibiotics. So what was making them sick? It turned out the antibiotics caused a defect in the anti-fungal immune response, specifically in the gut.

Antibiotic-treated mice had much higher levels of fungal infection in the intestines. The consequence of this was gut bacteria then escaped into the blood. The mice now had both a bacterial and a fungal infection to deal with, making them much sicker than the mice that did not have antibiotics.