CHARACTERIZATION OF SALMONELLA-DUBLIN AND SALMONELLA-TYPHIMURIUM (COPENHAGEN) ISOLATES FROM CATTLE

Eight Salmonella typhimurium (Copenhagen) and eight Salmonella dublin isolates from cattle were compared by their antibiotic resistance patt erns, by their production of colicin, aerobactin, haemolysin and capsu le, by their possession of transmissible R plasmids and the spvC gene, and by their ability to invade and replicate within cultured epitheli al cells. The two groups differed in their antibiotic resistance profi les, with more of the host-adapted S. dublin isolates resistant to tet racycline than were the non-host-adapted S. typhimurium (Copenhagen) g roup, but more of the S. typhimurium (Copenhagen) isolates resistant t o the other antibiotics tested. None of the isolates produced colicin, but all produced aerobactin. One isolate in each group was encapsulat ed All of the S. typhimurium (Copenhagen) and S. dublin isolates conta ined plasmids, and all of them contained the spvC-homologous sequences . Four of the S. typhimurium (Copenhagen) isolates were able to transf er an R plasmid to a recipient organism by conjugation. One of the fiv e S. dublin isolates, which showed resistance to some of the antibioti cs tested, was able to transfer an R plasmid by conjugation. Both grou ps of isolates invaded cultured epithelial cells to a similar degree a fter 1 h, but the S. dublin isolates reached significantly higher leve ls within the cells than did S. typhimurium (Copenhagen) after 9 h. Th is ability may, in part, explain the association of S. dublin with mor e severe forms of salmonellosis and prolonged carrier states. Further study of the intracellular growth of these isolates seems warranted.