Cross-resistance patterns among clinical isolates of Klebsiella pneumoniae with decreased susceptibility to cefuroxime

The frequency of decreased susceptibility to cefuroxime and quinolones and the correlation between these drug resistance traits was investigated in clinical isolates of Klebsiella pneumoniae from two Danish counties. Eighty-three randomly selected clinical isolates of K. pneumoniae with decreased susceptibility to cefuroxime were examined for cross-resistance patterns and the production of beta-lactamases. The frequency of resistance to cefuroxime and ciprofloxacin has increased from <5% in 1990 to 15% and 7% in 1998, respectively. Two of the 83 isolates were multiply resistant and seemed to produce extended-spectrum beta-lactamases. However, cross-resistance to ciprofloxacin and other classes of drug in 68% of the remaining isolates indicates that other resistance mechanisms, such as penetration barriers, had probably been selected in these Danish isolates. The susceptibility to ciprofloxacin decreased successively with decreasing susceptibility to cefuroxime for K. pneumoniae. This did not occur in cefuroxime-resistant Escherichia coli.