A pathogenic bacterium was obtained from the hepatopancreas of diseased Procambarus clarkii.The isolated strain was determined by physiological and biochemical analysis,16S rRNA sequencing and phylogenetic analysis.Then the sensitivity of the strain to 20 kinds of antibiotics and synergistic effects of antibiotics combined with natural compounds were determined by the agar diffusion method and checkerboard assay.The results showed that physiological and biochemical characters of the isolate were similar to that of Morganella morganii,and 16S rRNA sequence determination and phylogenetic analysis showed that the isolate sequence shared over 99% similarity to that of M. morganii.Taken together,the strain was identified as an M. morganii strain.The susceptibility study showed that the strain was sensitive to enrofloxacin,florfenicol,neomycin and other 4 kinds of antibiotics,and moderate sensitive to kanamycin,resistant to doxycycline,streptomycin,tetracycline and other 9 kinds of antibiotics.Moreover,the synergistic susceptibility showed that doxycycline combined with dihydrocapsaicin had synergistic effect.Taken together,the results demonstrated that the strain isolated from the hepatopancreas of diseased P. clarkii is a resistant M. organii.Florfenicol,enrofloxacin,neomycin and doxycycline combined with dihydrocapsaicin can be chosen as candidates for treatment of M. morgani infections.