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

Abstract

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 six strains belonged to phage types 35, 1, 24var (a variation of phage type 24), 9a, 1b and an unknown phage type. The majority of S.E. phage type 34 strains (eight of the 11) grouped at R 2≥0.45 into one RAPD-PCR cluster with two strains of phage types 4, a strain of phage type 24var and a strain of phage type 9a, indicating that they consist of a genetically heterogeneous collection of strains. Two of the remaining three phage type 34 strains grouped into two different clusters, well separated from the other phage type 34 strains. One strain of phage type 34 was genetically diverse and did not cluster with any of the strains included in this study. Three of the phage type 14 strains grouped into cluster II at R 2≥0.72, suggesting that they are genetically closely related. However, the remaining three strains of phage type 14 grouped into two separate clusters. Strains of phage types 7, 35, and 1 grouped in one cluster at R 2≥0.55. Our results clearly indicated that 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 different phage types. No specific plasmid profile could be linked to any of the phage types. Based on results obtained by LD 50 virulence tests, strains containing the 38 MDa plasmid are more virulent compared to strains which do not contain the plasmid.