A strain of Escherichia coli (MG/32) was recovered from the blood of a patient who had received ceftazidime for eight weeks. The isolate was resistant to ceftazidime but susceptible to other third-generation cephalosporins. Alterations in outer membrane proteins were implicated in this selective ceftazidime resistance.As ceftazidime susceptibility was regained, the quantity of outer membrane proteins of 37,000 and 39,000 molecular weight increased. Although the isolate possessed a TEM-1 β-lactamase, this enzyme was not involved in the selective resistance to ceftazidime; it did not disappear on reacquisition of ceftazidime susceptibility and did not hydrolyze the drug. Potassium c1avulanate enhanced the activity of ceftazidime against E. coli strain MG/32, but this enhancement was due to a direct effect on outer membrane proteins and not to β-Iactamase inhibition.
Bibliographical noteFunding Information:
Received for publication 8 September 1986, and in revised form 17 November 1986. This work was supported in part by a grant from the Health Future Foundation, Omaha, Nebraska. We thank Dr. Mary Gilchrist (Children's Hospital Medical Center, Cincinnati) for allowing us to analyze strain MG/32, Dr. Richard V. Goering for performing plasmid analyses, and Ellen S. Moland for technical assistance. Please address reprint requests to Dr. Johan S. Bakken, Department of Medical Microbiology, Creighton University School of Medicine, 2500 California Street, Omaha, Nebraska 68178. * Present address: Department of Microbiology, Repatriation Hospital, Hobart, Australia 7001.