Colistin-Resistant Acinetobacter baumannii Clinical Strains with Deficient Biofilm Formation

In two pairs of clinical colistin-susceptible/colistin-resistant (Cst(s)/Cst(r)) Acinetobacter baumannii strains, the Cst(r) strains showed significantly decreased biofilm formation in static and dynamic assays (P < 0.001) and lower relative fitness (P < 0.05) compared with those of the Cst(s) counterparts. The whole-genome sequencing comparison of strain pairs identified a mutation converting a stop codon to lysine (*241K) in LpsB (involved in lipopolysaccharide LPS synthesis) in one Cst(r) strain and a frameshift mutation in CarO and the loss of a 47,969-bp element containing multiple genes associated with biofilm production in the other.