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Antibiotic resistance is believed to come at a cost to the microorganism's fitness and virulence. An international research team decided to test this assumption, given that patients with cystic fibrosis can become persistently colonized with antibiotic-resistant Pseudomonas aeruginosa.
The researchers created a library of 300,000 transposon-insertion mutants of a well-defined P. aeruginosa strain. They then fed those mutant strains to mice in drinking water (to assess whether the strains can colonize the gut) and made the mice neutropenic (to assess the strains' ability to disseminate). Using high-throughput transposon-insertion-site sequencing, they found that strains with mutations of the oprD gene (which encodes an outer-membrane protein …