We studied 247 strains of Proteus mirabilis collected during the 6 months from November 2003 to April 2004 from 12 clinical laboratories in the Kinki region of Japan for the production of extended-spectrum beta-lactamase (ESBL). Eighteen strains (7.3%) showed MICs for cefpodoxime of > or = 2 microg/mL and 13 strains (5.2%) were positive for the double-disk synergy test. Susceptibility depended on genotype. MICs for cefepime, cefozopran, and cefpirome were high (> or = 8 microg/mL), and that for ceftazidime was low (0.12-0.5 microg/mL). Meropenem showed the lowest MIC (< or = 0.03-0.25 microg/mL) of the calbapenems, while other calbapenems showed somewhat higher values (0.5-2 microg/mL). The MIC of tazobactam/piperacillin was also relatively low (< or = 0.25-1 microg/mL). Analysis of the ESBL genotype by the polymerase chain reaction showed that 12 of 13 strains were CTX-M2 types. CTX-M9 was detected in a single laboratory. The clinical background showed 5 strains in urine samples. Twelve of 13 strains were detected in patients with minimal devices use. No symptoms were found in most cases of established syndrome. Analysis of PCR fingerprint profiles of random amplified polymorphic DNA patterns showed that 6 of 7 strains from hospital 1 showed the same pattern, and 5 of 5 strains from hospital 13 showed the same pattern, suggesting the nosocomial spread of P. mirabilis in each hospital.