Agglutination with O antisera of salmonella exposed to antibiotics.

Five strains of Salmonella were grown on agar containing subinhibitory concentrations of ampicillin, gentamicin, tetracycline, or chloramphenicol, and on drug-free agar (control). Antigens were prepared by heating bacteria suspensions in saline solution at 100 C or by suspension in alcohol. Antigens were tested for agglutinability with somatic O antisera and fluorescent antibody staining. The alcohol-treated antigens prepared from organisms grown in the presence of antibiotics other than ampicillin had lower agglutination titers than did the control grown on drug-free agar. Heat-treated control antigens had lower agglutination titers than did the alcohol-treated control antigens. The agglutinability of heat-treated antigens prepared from organisms that had been exposed to antibiotics was preserved or enhanced. The agglutinated filaments produced a flocculent sediment, in contrast to the granular sediment of the controls. No significant morphologic abnormality in cell-wall structures of antibiotic-exposed cells could be detected by either electron microscopy or the fluorescent antibody staining.