FIGURE 1.

The evolutionary pathway of colistin resistance in Acinetobacter baumannii 17978 in solid agar and liquid medium. (A) Four colonies of A. baumannii ATCC 17978 were inoculated in a solid agar plate containing 10 mg/L colistin and serially passaged for 15 days. Then, one colony was continuously cultured with 10 mg/L colistin on agar plates for 45 days. Another colony was streaked on 50 mg/L colistin plates for a 15 days serial passage. Then, the bacteria were streaked onto 100 and 200 mg/L colistin plates for 15 days. The strains were stored at -80°C every 15 days. The final strains were sent for whole genome sequencing. The mutations were detected by breseq, which mapped the sequenced reads onto the reference genome. The mutation sites in the final strain were identified by PCR and Sanger sequencing. The mutations related to colistin resistance or fitness are labeled above the strain. (B) One lineage of A. baumannii 17978 was inoculated in Mueller Broth (MH) medium with increasing concentrations of colistin for 12 days. The final strains were sent for whole genome sequencing. The mutations were detected by breseq, which mapped the sequenced reads onto the reference genome. The mutations related to colistin resistance or fitness are labeled above the strain.