[Antibody induced phase variation in Pseudomonas aeruginosa (author's transl)].

To extend the flagella specific H antigenic schema of P. aeruginosa (ANSORG, 1978), investigations are carried out to reveal phase variation in this species as in Salmonella or Arizona. With conventional methods, i.e. examination of single colonies after plating the cultures on standard nutrient agar or the phase reversal techniques of Craigie (1931) and Gard (1938) by adding homologous anti-OH-serum of different amounts in semisolid agar medium, no change of the flagellar antigens of various P. aeruginosa strains is observed using the indirect fluorescent antibody technique. When subcultivated in pure homologous anti-OH-serum, however, the cells express stepwise a second H phase, which is different from the original flagellar antigens. In control experiments with serum from non-immunized rabbits the original flagellar antigens remain constant. The phase variation affects only the H antigen, is reversible by cultivation on soft agar medium and is characterized by the nonspecific type-overlapping antigen u. After absorption of immunserum prepared with cells cultivated in homologous anti-OH-serum by cells cultivated on soft agar medium, an antiserum specific for factor u is obtained. Since fresh isolates do not react with anti-u-serum, the diphasic nature of P. aeruginosa is probably of minor significance for H typing in practice.