Effectiveness of antibiotics significantly reduced when multiple bugs present

A study shows that higher doses of antibiotics are needed to eliminate abacterial infections of the airways when other microbes are present. It helps explain why people with lung diseases often have respiratory infections despite treatment.

Researchers say that even a low level of one type of microbe in the airways can have a profound effect on the way other microbes respond to antibiotics.

The results show the need to consider the interaction between different species of microbe when treating infections with antibiotics.

People with chronic infections often have co-infection with several pathogens, but the problem is we don't take that into account in deciding how much of a particular antibiotic to treat them. Thomas O&Brien carried out the research for his PhD at the University of Cambridge.

Antibiotics are difficult to cure chronic infections in the human airway. Although these types of infections are associated with a single species, the site is often co-colonized by a number of other microbes.

Treatment options usually focus on targeting the pathogen, and don't take into account the co-habiting species. The treatments fail to resolve the problem. Scientists have had no idea why this is.

To get their results, the team created a simplified model of the human airways, containing artificial sputum, which mimics the real phlegm coughed up during an infection.

They were able to grow a mixture of different microbes in a stable way for weeks at a time. The experiment is novel because usually one pathogen will outgrow the others very quickly. The researchers were able to study infections with multiple species of microbe in the laboratory.

The three microbes that were used in the experiment were thebacteria Pseudomonas aeruginosa and Staphylococcus aureus, and the fungus Candida albicans.

The researchers used an antibiotic called colistin to kill the microbes. The antibiotic didn't work when the other pathogens were present.

We were surprised to find that an antibiotic that we know should clear an infection of Pseudomonas didn't work in our lab model when other bugs were present.

The effect was the same when the mix was treated with fusidic acid and fluconazole.

The researchers found that the higher the dose of the antibiotic, the harder it was to kill the bacteria.

The three species-specific antibiotics were less effective against their target when three pathogens were present together, according to the senior author of the paper.

Antibiotics are usually only tested against the main pathogen in order to determine the lowest effective dose. This study helps explain why the same dose is often not enough to treat an infectious disease. Potential new antibiotics will be tested against a mixture of microbe species with the help of a new model system.

There are infections in the lungs of people with the disease. These infections can persist even after strong antibiotics are used. People with asthma andCOPD are more likely to have chronic infections of the airways.

By looking at the genetic code of the Pseudomonasbacteria in their lab-grown mix, the researchers were able to identify certain genes that give rise to antibiotic resistance. When other pathogens are present, the mutations arise more frequently.

Human patients who have been treated with colistin have had the same genetic changes as the 800 samples of Pseudomonas from around the world.

As soon as you use an antibiotic to treat a bug, it will start to evolve resistance. Since colistin started to be used, that has happened. This is a reminder of the need to find new antibiotics to treat human infections.

More information: Thomas James O'Brien et al, Decreased efficacy of antimicrobial agents in a polymicrobial environment, The ISME Journal (2022). DOI: 10.1038/s41396-022-01218-7 Journal information: ISME Journal Citation: Effectiveness of antibiotics significantly reduced when multiple bugs present (2022, March 19) retrieved 19 March 2022 from https://phys.org/news/2022-03-effectiveness-antibiotics-significantly-multiple-bugs.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.