Antigenic changes in Pseudomonas aeruginosa in vivo and after lysogenization in vitro.

Pseudomonas aeruginosa cultures not conforming in antigenic structure to established serogroups were isolated from infants and from infants and from 23 O antigen type strains lysogenized with 22 different phages in vitro. The derivatives, characterized by smooth colonial form and heat stability, retained at least part of the antigens of the parent strains and became agglutinable in certain heterologous sera. All derivatives showed immunoelectrophoretic patterns identical with those of the parent strains. Antigenic analysis showed the presence of factors in the derivatives identical with (italicized figures), bilaterally related to (non-bracketed figures) or unilaterally related to (bracketed figures) O antigens of LANYI's schema: (i) changes in vivo, 01 leads to 01, (O8); O11a, 11b leads to O11a, 11c; (ii) changes in vitro, O1 leads to O1, (O8); O4a, 4b leads to O4a,4b,O1,O8,(O10a), O11; O4a,4b leads to O4a,4b,O1,O8,O10a,O11; O4a,4c leads to O4a,4c,O1,(O8),(O10a),(O11). The antigenic changes were accompanied usually by a loss of sensitivity to several typing phages and the lytic spectrum of phages released from the derivatives had become narrower. The findings suggest that multiple agglutinability of P. aeruginosa frequently encountered in nature is associated with phage action.