Novel Mechanism for Fluoroquinolone Resistance in Acinetobacter baumannii

An EZ::TN<R6Kγori/KAN-2>Tnp transposon insertion in an open reading frame of unknown function (ncr) in Acinetobacter baumannii resulted in an 8-fold increase in ciprofloxacin resistance (Cip(r)). Transposon insertions in an ncr mutant that reduced Cip(r) back to wild type mapped to three genes encoding subunits of the RecCBD exonuclease. The ncr mutation increased transcription of the recCBD genes, and overexpression of the recCBD genes in a wild-type background resulted in a 4-fold increase in Cip(r).