Effect of selected plasmids on the serum sensitivity of Salmonella typhimurium strains with defined lipopolysaccharide core defects

A set of transductants derived from a smooth Salmonella typhimurium strain were tested for their sensitivity to human serum. The transductants used were distinguishable by the length of the core of oligosaccharide portion of their lipopolysaccharide. The smooth SL3770 strain is the most resistant and each rougher member of the set is more sensitive than the preceding one. These transductants were used to determine the effect of plasmids R1, RN3, Rs‐a and Rtsl on serum sensitivity. R1 and RN3 did not confer any change in serum resistance, while Rs‐a increased resistance and Rtsl decreased serum resistance.