Inhibition of gene transfer by antiserum and identification of serotypes of sex pili.

Gene transfer by conjugation due to F or R (drug resistance) factors is inhibited by antibody to the sex pili. Serological analysis is able to distinguish between the sex pili determined by closely related sex factors, and the specificity of inhibition of transfer agrees with that previously determined by direct electron microscopical observation of antibody bound to the sex pili (10). Inhibition of transfer can therefore be applied to the identification of wild-type R factors with repressed sex factors that determine too few pili to be examined directly. It can also be used to differentiate the activities of two unrelated sex factors in the same donor bacterium.