Background: In order to provide a guideline for empirical treatment of urinary tract infections, we studied a change in causative organisms and antimicrobial susceptibility in our region of an island.

Methods: We reviewed the results of antimicrobial susceptibility and the hospital charts of 3,064 patients with a significant bacteriuria (more than 10⁵ colony forming unit/mL in urine cultures); the patients had been admitted to or seen at the out-patient clinic of Cheju University Hospital during the period from January 2002 to December 2005.

Results: The most common pathogens were Escherichia coli (44.9%), Klebsiella spp. (8.1%), and Pseudomonas spp. (7.0%). In E. coli, the mean percent resistance to ampicillin, trimethoprim-sulfamethoxazole, and ciprofloxacin during the 4-year period was 69.0%, 32.5%, and 24.7%, respectively.

Conclusion: An increasing resistance of common urinary pathogens to known empirical agents such as ampicillin, trimethoprim-sulfamethoxazole, and ciprofloxacin caused a need for a more updated guideline in our region of an island. (Korean J Clin Microbiol 2007;10:19-24)