title: Clinically significant borderline resistance of sequential clinical isolates of Klebsiella pneumoniae.
abstract: Two sequential clinical isolates of Klebsiella pneumoniae (Kpn) were isolated from bronchoalveolar lavage fluid (Kpn#1) and sputum (Kpn#2) of a patient with pneumonia, complicated by anatomical and immunosuppressive problems due to Wegener's granulomatosis. Despite 4 weeks of systemic treatment with ciprofloxacin (CIP) Kpn#2 was isolated thereafter. A fluoroquinolone-resistant mutant (Kpn#1-SEL) was derived from Kpn#1 in vitro by selecting on agar plates supplemented with ofloxacin. Kpn#1, Kpn#1-SEL and Kpn#2 had an identical pattern in PFGE. CIP MICs were 0.25, 2 and 4 mg/l for Kpn#1, Kpn#2 and Kpn#1-SEL, respectively. Kpn ATCC 10031 (CIP MIC 0.002 mg/l) served as control. We analyzed mechanisms of fluoroquinolone resistance by determining antibiotic susceptibility, organic solvent tolerance, accumulation of fluoroquinolones, dominance testing with wild-type topoisomerase genes (gyrA/B, parC/E), sequencing of the quinolone resistance determining regions of gyrA/B, parC/E and marR and Northern blotting of marR and acrAB genes. Compared with Kpn ATCC 10031, elevated MICs to fluoroquinolones and unrelated antibiotics in Kpn#1 was presumably due to a primary efflux pump other than AcrAB and increased the CIP MIC 125-fold. Although Kpn#1 tested sensitive according to NCCLS breakpoints, the elevated CIP MIC of 0.25 mg/l presumably rendered this isolate clinically resistant and lead to therapeutic failure in this case. Further increase of MIC to fluoroquinolones in vivo and in vitro was distinct. Kpn#1-SEL, selected in vitro, acquired a GyrA target mutation, whereas in Kpn#2 no known resistance mechanism could be detected.
authors.affiliation: Institute for Medical Microbiology and Hygiene, University of Regensburg, Regensburg, Germany. wagenlehner@aol.com
authors.forename: F M E
authors.initials: FM
authors.lastname: Wagenlehner
authors.forename: P
authors.initials: P
authors.lastname: Heisig
authors.forename: C
authors.initials: C
authors.lastname: Irtenkauf
authors.forename: F
authors.initials: F
authors.lastname: Notka
authors.forename: J
authors.initials: J
authors.lastname: Decker
authors.forename: N
authors.initials: N
authors.lastname: Lehn
authors.forename: H
authors.initials: H
authors.lastname: Linde
mesh_terms: D015152:Blotting, Northern; D002939:Ciprofloxacin / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D006801:Humans; D007711:Klebsiella pneumoniae / Q000187:drug effects* / Q000235:genetics; D008826:Microbial Sensitivity Tests
chemical_list: D002939:Ciprofloxacin