Identification of strains of Citrobacter genomospecies 10 isolated from well water

Twenty one strains (54%) of Citrobacter genomospecies 10 were identified fr om 39 strains of citrobacteria isolated from well water in the region of No rth Moravia during one year. Two strains of genomospecies 10 isolated from raw milk and milking machines (Urbanova and Pacova, 1997) were added to the collection of 21 strains and so the total of 23 strains were studied. It i s probable that the origin of the strains from milk sources is water, too. The strains were identified using the commercial kit ENTEROtest 16 (Lachema , a.s., Brno) including OXItest and ONPtest supplemented with the following rests: arginine dihydrolase, sodium acetate, melibiose, raffinose, dulcito l, alpha-methyl-D-glucoside. The current database of numerical identificati on system TNW (Czech Collection of Microorganisms, Masaryk University, Brno ) does not contain any reference data for identification of genomospecies 1 0, therefore the result of identification - Citrobacter werkmanii - was inc orrect (Tab. II). Both C. werkmanii and genomospecies 10 are ornithine and indolle negative, malonate positive. The two characteristics useful for the ir differentiation are inability of genomospecies 10 to hydrolyze urea and inability to utilize sodium citrate as a sole carbon source. Some minor dif ferences between the biochemical results reported in Tab. I and those repor ted for the three strains of genomospecies 10 by Brenner et al. (1993) and O'Hara er al. (1995) are as follows: 96% (previously 67%) H2S positive, 4% (previously 0%) esculin positive, 74% (previously 100%) delayed Simmons cit rate positive, 100% (previously 67%,) melibiose and cellobiose positive, 0% (previously 100%) delayed arginine dihydrolase positive. It is probable th at genomospecies 10 is one of the citrobacteria most frequently isolated fr om well water which were previously identified as Citrobacter freundii. Fou r representative strains of this genomospecies were kindly reidentified by O'Hara in CDC Atlanta, U.S.A. These strains have been deposited in our Coll ection as Citrobacter sp. (genomospecies 10): CCM 4513 (= CDC 4562-98, milk ing machine), CCM 4514 (= CDC 4563-98, raw milk), CCM 4515 and CCM 4711 (= CDC 4564-98 and CDC 4565-98, well water).