Clinically significant borderline resistance of sequential clinical isolates of Klebsiella pneumoniae.
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.
Wagenlehner
F M E
FM
Institute for Medical Microbiology and Hygiene, University of Regensburg, Regensburg, Germany. wagenlehner@aol.com
Heisig
P
P
Irtenkauf
C
C
Notka
F
F
Decker
J
J
Lehn
N
N
Linde
H
H
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
D002939:Ciprofloxacin