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Three smooth strains of urinary Escherichia coli were grown in a chemostat under carbon-limited (C-lim) and magnesium-limited (Mg-lim) conditions over a range of dilution rates (D). Strain LP1674 was resistant to human serum under C-lim but became sensitive when grown under Mg-lim, the degree of sensitivity increasing as D increased. The transition to serum sensitivity was accompanied by loss of ability to produce extractable K1 antigen and a reduction in the amount of a 46k envelope polypeptide. C-lim cells of strain LP729 exhibited a delayed sensitive response to serum, the degree of lag in serum killing becoming less pronounced with increasing values of D; Mg-lim cells were more sensitive with little or no lag in serum killing. The degree of lag appeared to be directly related to the amount of the O side-chain sugar mannose associated with the lipopolysaccharide. C-lim and Mg-lim cultures of E. coli strain LP1395 were resistant to serum except when growing at near maximal rates. Although C-lim cultures contained more acidic polysaccharide than Mg-lim cells, transition to serum sensitivity did not appear to be related to exopolysaccharide production. Rapidly growing cells of strain LP1395 did, however, have lower lipopolysaccharide 0 side-chain sugar:core-sugar ratios than more slowly growing cells. With all three strains, changes in dilution rate and in the nature of the limiting nutrient were accompanied by changes in envelope protein composition. This study demonstrates that many cell-surface changes occur in response to alterations in the growth environment and some of these may be correlated with changes in sensitivity to serum.

Effect of the growth environment on cell-envelope components of Escherichia coli in relation to sensitivity to human serum