The Effect of Nutrient Limitation and R-plasmids on the Properties of Escherichia Coli

Abstract

When simple salts media were formulated for the growth of Escherichia coli K12 W3110, with (R+) and without (R-) the R-plasmid RP1, it was found that the growth yield of E. coli R+ was lower than that of R- for magnesium, potassium and phosphate, although the glucose and nitrogen requirements were the same. In addition, E. coli R+ required added ferrous ion at high cell concentrations. RP1 was stable in such media and also during storage on simple salts agar, although it was relatively unstable when stored on nutrient agar. RP1 lowered the minimum inhibitory concentrations in nutrient broth of cetrimide and chlorhexidine, but did not affect that of phenol. In simple salts media, the sensitivity to disinfectants varied with nutrient-depletion. E. coli R+ was more sensitive to chlorhexidine than R-, but magnesium (-Mg) or phosphate (-P)-depleted cells were more resistant than carbon(-C)-depleted ones. E. coli R+ (-C) was also more sensitive to cetrimide than R- (-C), but whereas (-P) increased the sensitivity of both cultures, (-Mg) increased the sensitivity of R- and decreased that of R+. R+ and R- (-C) had the same sensitivity to phenols; (-P) or (-Mg) had the same effect as on cetrimide sensitivity. Although nutrient-depletion and RP1 caused changes in surface charge, these could not be correlated with changes in resistance.