A monoclonal antibody (MAb), MO15, was raised against the lipopolysaccharid
e antigen of an epsilon 15-lysogenized serogroup E-1 Salmonella strain. The
O factor 15-specific MAb MO15, together with another serogroup E-specific
MAb, can differentiate among phage lysogenization variants in serogroup E s
almonellae. Their epitope specificities in relation to conventional O-antig
enic structures are discussed.