Agitation during incubation reduces the time required for a lysine microbiological growth assay using an Escherichia coli auxotrophic mutant

Microbiological assays involving Escherichia coil lysine auxotrophs must be optimized to facilitate routine use. Our objectives in this study were to characterize growth of an auxotrophic E. coli lysine mutant(American Type C ulture Collection strain #23812) and examine the effect of agitation on E. coli mutant growth. A defined minimal salts basal medium was used and suppl emented with various lysine concentrations. The E. coli lysine auxotroph re sponded to increasing lysine concentration with increasing optical density. When maximum optical density (MOD) was determined for the auxotroph, a lin ear increase was obtained as lysine concentrations were increased (R-2 +/- 0.96) for both agitation and static cultures. Growth rates were not signifi cantly (p > 0.05) affected by lysine concentrations, cultural conditions or their combined effect. However, growth with agitation significantly (p < 0 .05) reduced the assay time by shortening the lag phase and causing station ary phase to occur earlier. The Values of R-2 (greater than or equal to 0.9 6) relatively remained constant over the range while the bacterial populati on were in the stationary phase. In conclusion, the lysine growth assay usi ng the E, coli lysine auxotroph can be made more rapid by agitating the cul ture during incubation.