DIFFERENTIATION OF KLUYVERA-CRYOCRESCENS FROM KLUYVERA-ASCORBATA BY IRGASAN SUSCEPTIBILITY TESTING

From the faeces of a diarrhoeic patient, we isolated a strain of Kluyvera ascorbata on cefsulodin-irgasan-novobiocin (CIN) agar, a highly selective medium used for Yersinia enterocolitica. Since no selective media have been described for Kluyvera spp., we tested 5 strains each of K. ascorbata and K. cryocrescens for their ability to grow on CIN agar. K. ascorbata exhibited an inhibition on CIN of less than 10% CFU compared to blood agar, whereas K. cryocrescens did not grow at all even with inocula as high as 105 CFU per plate. This phenomenon correlated very well with MIC values to irgasan, which were > 128 mg/l for K. ascorbata and .ltoreq. 0.25 mg/l for K. cryocrescens. No significant differences between the two species were observed for the other two antibiotics contained in CIN. This phenotypic character has been used to differentiate 18 strains belonging to either species on the basis of a simple disk test: with disks containing 5, 25 or 125 .mu.g irgasan, K. ascorbata never showed zones of inhibition, whereas K. cryocrescens produced zones of .gtoreq. 15%, .gtoreq. 21.5 and .gtoreq. 25.0 mm in diameter, respectively.