Epidemiology and Infection

Phage type conversion in Salmonella enterica serotype Enteritidis caused by the introduction of a resistance plasmid of incompatibility group X (IncX)

D. J. BROWN a1c1, D. L. BAGGESEN a2, D. J. PLATT a3 and J. E. OLSEN a1
a1 Department of Veterinary Microbiology, The Royal Veterinary and Agricultural University, 4 Stigbjlen, DK 1870 Frederiksberg C., Denmark
a2 Danish Veterinary Laboratory, 27 Bülowsvej, DK-1790, Copenhagen V, Denmark
a3 University Department of Bacteriology, Royal Infirmary, Castle Street, Glasgow G4 0SF, Scotland


The plasmid pOG670, a 54 kb, conjugative plasmid that specifies resistance to ampicillin and kanamycin and belonging to the incompatibility group X (IncX), was transferred into 10 isolates of Salmonella enterica serotype Enteritidis belonging to 10 different phage types (PT1, 2, 3, 4, 8, 9, 9b, 10, 11 and 13). Acquisition of the plasmid by these strains did not result in the loss of any resident plasmids but resulted in phage type conversion in 8 of the 10 strains (PT1, 2, 4, 8, 9, 9b, 10 and 11). The observed changes in phage type were found to result from the loss of sensitivity to 3 of the 10 typing phages used (phages 3, 5 and 7). Where the conversion resulted in a change to a defined phage type, both the new and original PTs belonged to the same, previously described, evolutionary lines. Enteritidis PTs 1, 4 and 8, commonly associated with poultry world-wide, were converted to PTs 21, 6 and 13a respectively. The results indicate a different route for phage type conversion Enteritidis from others reported in the literature and, although IncX plasmids are not normally present in PT8 or PT13a, may suggest a possible mechanism/link connecting these phage types.

(Accepted September 9 1998)

c1 Author for correspondence.