The results highlight the need to consider interactions between different bacterial species when treating infections with antibiotics – and adjust dosage accordingly.
Mr. Thomas O’Brien, who conducted the research chapter for his PhD in the Department of Biochemistry at the University of Cambridge.
O’Brien added: “Our results may help explain why in these people antibiotics are not working as well as they should be.
Chronic bacterial infections such as those in the human respiratory tract are difficult to cure with the use of antibiotics.
Although these types of infections are often associated with a single pathogenic species, the site of infection is often colonized by several other bacteria, most of which are not usually pathogenic in their own right.
Treatment options often revolve around targeting the pathogen and are of little concern to cohabiting species. However, these treatments often do not resolve the infection.
In the study, the team developed a simplified model of the human respiratory tract, containing artificial sputum (‘sputum’) designed to chemically resemble real sputum coughed up during an infection, full of bacteria.
The model allowed them to grow a mixture of different microorganisms, including pathogens, consistently for weeks at a time.
This is novel, because usually one pathogen will outgrow others and ruin the experiment. It allows researchers to replicate and study infections with multiple species of bacteria, known as ‘multimicrobial infections’, in the laboratory.
The three bacteria used in the experiment were the bacteria Pseudomonas aeruginosa and Staphylococcus aureus, and the fungus Candida albicans, a combination commonly found in the airways of people with cystic fibrosis.
The researchers treated this mixture of bacteria with an antibiotic called colistin, which is very effective at killing Pseudomonas aeruginosa. But when other pathogens show up alongside Pseudomonas aeruginosa, antibiotics don’t work.
Wendy Figueroa-Chavez at the University’s Department of Biochemistry, said: “We were surprised to find that an antibiotic that we knew could effectively clear Pseudomonas infection was inactive in tissue. picture of our lab in the presence of other bugs.”
The same effect occurred when the microbial mixture was treated with fusidic acid – an antibiotic that specifically targets Staphylococcus aureus and with fluconazole – an antibiotic that specifically targets Candida albicans.