Isolation of a temperate bacteriophage encoding the type III effector protein SopE from an epidemic Salmonella typhimurium strain

Abstract

Salmonella typhimurium employs the specialized type III secretion system encoded in pathogenicity island 1 (SPI1) to translocate effector proteins into host cells and to modulate host cell signal transduction. The SPI1 type III system and the effector proteins are conserved among all salmonellae and are thought to be acquired by horizontal gene transfer. The genetic mechanisms mediating this horizontal transfer are unknown. Here, we describe that SopE, a SPI1-dependent translocated effector protein, is present in relatively few S. typhimurium isolates. We have isolated a temperate phage that encodes SopE. Phage morphology and DNA hybridization, as well as partial sequence information, suggest that this phage (SopE⌽) is a new member of the P2 family of bacteriophages. By lysogenic conversion this phage can horizontally transfer genes between different S. typhimurium strains. Strikingly, most of the isolates harboring SopE⌽ belong to the small group of epidemic strains of S. typhimurium that have been responsible for a large percentage of human and animal salmonellosis and have persisted for a long period of time. Our data suggest that horizontal transfer of type III dependent effector proteins by lysogenic infection with bacteriophages (lysogenic conversion) may provide an efficient mechanism for fine-tuning the interaction of Salmonella spp. with their hosts.

Salmonella Typhi: from a Human Pathogen to a Vaccine Vector

“…In addition, SPI-7 has a viaB operon which encodes the gene responsible for the synthesis and transport of the virulence antigen Vi (28,29). Studies have shown that Vi antigen may be important in the survival of the bacterium within macrophages though this may not be in cellular invasion of the macrophage or the intestinal wall (14,30).…”

Emergence of Salmonella epidemics: The problems related to Salmonella enterica serotyp Enteritidis and multiple antibiotic resistance in other major serotypes

“…Recent studies have shown that acquired PAI are major contributors to the virulence nature of many pathogenic bacteria [60,63], including Salmonella where they are referred to as Salmonella Pathogenicity Islands (SPI). These chromosomally encoded regions typically contain large clusters of virulence genes and have the potential to increase the virulence of a micro-organism or even to transform a benign organism into a pathogen [100]. Until now, 12 SPI have been described.…”

Bacteriophage P2

“…83 The P2-related Salmonella phage sopEf encodes, at this same location, the type III effector SopE, a virulence factor injected into eukaryotic cells via the Salmonella enterica type III secretion system. 84 Orf30 lies between genes S and V. It is nonessential, and transcribed constitutively from its own promoter at a low level. 49 Homologues of the predicted orf30 gene product are found in many E. coli genomes, but its function remains unknown.…”