Characterization of South African isolates of Salmonella enteritidis by phage typing, numerical analysis of RAPD-PCR banding patterns and plasmid profiles

Eleven of the 33 strains of Salmonella enteritidis (S.E.) included in this study belonged to phage type 34. Six strains belonged to phage type 14, six strains to phage type 4 and four strains to phage type 7. The remaining si x strains belonged to phage types 35, 1, 24var (a variation of phage type 2 4), 9a, Ib and an unknown phage type. The majority of S.E. phage type 34 st rains (eight of the 11) grouped at R-2 greater than or equal to 0.45 into o ne RAPD-PCR cluster with two strains of phage types 4, a strain of phage ty pe 24var and a strain of phage type 9a, indicating that they consist of a g enetically heterogeneous collection of strains. Two of the remaining three phage type 34 strains grouped into two different clusters, well separated f rom the other phage type 34 strains. One strain of phage type 34 was generi cally diverse and did not cluster with any of the strains included in this study. Three of the phage type 14 strains grouped into duster II at R-2 gre ater than or equal to 0.72, suggesting that they are genetically closely re lated. However, the remaining three strains of phage type 14 grouped into t wo separate clusters. Strains of phage types 7, 35. and 1 grouped in one cl uster at R-2 greater than or equal to 0.55. Our results clearly indicated t hat S.E. strains of the same phage type are not always genetically related. On the other hand, strains of a high genetic relatedness classified as dif ferent phage types. No specific plasmid profile could he linked to any of t he phage types. Based on results obtained by LD50 virulence tests, strains containing the 38 MDa plasmid are more virulent compared to strains which d o not contain the plasmid. (C) 2001 Elsevier Science B.V. All rights reserv ed.