The purpose of this report was to determine the frequency of colonization and bacteremia with ceftazidime-resistant Klebsiella pneumoniae among pediatric candidates for and recipients of liver (LTx) and/or intestinal (ITx) transplantation. Between January and December 1994, surveillance stool cultures obtained from 51 children on the abdominal transplant service were planted on a selective medium containing 2 microg/ml of ceftazidime. Isolates of K. pneumoniae which grew on the selective medium were screened for extended-spectrum beta-lactamase (ESBL) production by the double-disk synergy test and underwent microdilutional susceptibility testing. Strain relatedness of ceftazidime-resistant K. pneumoniae was analyzed by field inversion gel electrophoresis (FIGE). Sixteen of 51 patients had > or = 1 positive stool cultures for ceftazidime-resistant K. pneumoniae; 9 out of 16 on the first culture obtained 1-23 days (median = 5) after admission. All 9 had been in hospital prior to this admission. Four others were positive on their first culture but were in our hospital for > 1 month at the onset of the study. Three patients became colonized after admission. Colonization with ceftazidime-resistant K. pneumoniae was more frequent among recipients of ITx (including combined LTx-ITx) compared to LTx alone (7/13 vs. 7/32, p<0.05). All of the ceftazidime-resistant isolates recovered from surveillance stool cultures had positive double-disk diffusion tests suggesting the presence of ESBL production as the mechanism of resistance. Ceftazidime resistance was identified in 7/8 episodes of bacteremia due to K. pneumoniae in patients on the abdominal transplant service compared with 0/17 episodes in other children in the Children's Hospital of Pittsburgh during the study. During this same time period, 69/312 clinical isolates of K. pneumoniae evaluated in the hospital laboratory were ceftazidime-resistant; 67/69 came from patients on this service. In none of the 312 isolates was resistance to cefotaxime found in the absence of ceftazidime resistance. Unique clones were identified for 10/19 isolates of ceftazidime-resistant strains of K. pneumoniae analyzed by FIGE. Colonization and bacteremia with ceftazidime-resistant K. pneumoniae were commonly identified among recipients of LTx & ITx at the Children's Hospital of Pittsburgh. The mechanism of resistance appeared to be due to the presence of ESBL production by resistant strains. Although resistant strains were frequently recovered from patients on the abdominal transplant service, recovery of ceftazidime-resistant strains from patients outside of this service was rare even in the intensive care setting.