Characterization of bacteriophages used in the Salmonella enterica serovar Enteritidis phage-typing scheme

1 National University of Ireland Galway, Galway, Republic of Ireland 2 National Salmonella Reference Laboratory, Galway, Republic of Ireland Correspondence N. De Lappe nialldinsrl{at}netscape.net Received January 2, 2008 Accepted September 15, 2008 The 16 Salmonella enterica serovar Enteritidis ( S . Enteritidis) typing phages (SETPs) used in the Laboratory of Enteric Pathogens (Health Protection Agency, London, UK) phage-typing scheme have not previously been characterized in detail. We have examined the adsorption properties of the phages with respect to a number of S. enterica serovars and defined phage morphology with electron microscopy. PFGE was used to estimate overall genome size and banding patterns generated by electrophoresis following restriction endonuclease digestion of the genome with Hin dIII were compared. PCR amplification and sequencing of selected genes was performed. The 16 phages comprise three morphotypes, Podoviridae (SETP1, 8, 10, 14, 15 and 16), Siphoviridae (SETP3, 5, 7, 11, 12 and 13) and Myoviridae (SETP2, 4, 6 and 9). All Podoviridae and Siphoviridae , but not Myoviridae, adsorbed to the O12 lipopolysaccharide antigen of Salmonella serogroups B (4,12) and D 1 (9,12). The genome sizes for the Podoviridae and Siphoviridae (PFGE-A) were approximately 42 kb. The genome size for Myoviridae SETP2, 4 and 9 was 36.5 kb, and for myovirus SETP6 was 27 kb. Hin dIII digestion of phage DNA produced 9 distinct patterns of 8 to 11 bands. Relationships between phages based on digest patterns were consistent with those defined by morphology. The Podoviridae had homologues of several P22 genes while the Siphoviridae had homologues of several genes present in the sequenced siphovirus SETP3 (EF177456 ). This study represents an initial step in characterizing the molecular basis that underlies the widely used S . Enteritidis typing scheme. Abbreviations: LEP, Laboratory of Enteric Pathogens; PT, phage type; SETP, Salmonella enterica serovar Enteritidis typing phage. The GenBank/EMBL/DDBJ accession numbers for the gene sequences of the Salmonella phages are EF151167–EF151189 and EF212157–EF21277. Tables of primers, phage typing and induction data, and sequence data are available as supplementary material with the online version of this paper.