What can reduce the effectiveness of antibiotics against bacteria? Scientists from the University of Cambridge decided to look into this question, the ISME journal writes. With the help of innovative technology, the specialists grew a mixture of different microbes during one week. It was not easy to do, because usually one pathogen stops growing before the others and spoils the experience. The researchers used what they called polymicrobial infections, which included the bacteria Pseudomonas aeruginosa and Staphylococcus aureus, as well as the fungal infection Candida albicans, which is the combination usually present in the airways of people with cystic fibrosis. Scientists then added an antibiotic called colistin, which is effective in killing Pseudomonas bacillus. But if other pathogens were present along with Pseudomonas, the antibiotic did not work. The same effect was observed when the samples were treated with fusidic acid (an antibiotic to treat Staphylococcus aureus) and fluconazole (an antifungal drug designed to kill Candida albicans). As it turned out, a lot more antibiotics are needed to effectively kill bacteria in polymicrobial infections, as their effectiveness decreases if there is more than one pathogen. According to the scientists, the findings will make it possible to test the effectiveness of new drugs against a mixture of different infections and microbes.