A Klebsiella oxytoca isolate which can produce significant levels of an exopolysaccharide using whey as a growth substrate has been reported. The plasmid profile of this isolate was shown to be different from that of the non-exopolysaccharide-producing K. oxytoca ATCC 43863. Irreversible curing of the single plasmid in the K. oxytoca isolate was achieved using 30 μg acriflavin/ml. The ability to produce the exopolysaccharide was lost with the curing of the plasmid (parent strain produced a medium viscosity of 1260 cP at 1 s−1 compared to 1.6 cP at 200 s−1 produced by the cured strain). However, the ability to metabolize lactose was not significantly affected by curing, and both the parent and the cured strain produced similar levels of viable cells (∼109 cfu/ml) after 62 h growth on lactose-rich medium. The exopolysaccharide-producing ability of the isolate was stable for at least 139 generations.