Abstract
This study identifies a strain of Salmonella enterica subspecies enterica serovar Enteritidis that harbors a highly unusual virulence plasmid. During the characterisation of a group of S. Enteritidis isolates, 10 isolates recovered from Canadian duck production facilities, of which seven were phage type 9b and three were closely related atypical phage types, failed detection by a PCR targeting the prot6e gene, a marker located on the virulence plasmid often employed for identification of this serovar. Comparison to prot6e+ isolates by several standard genetic typing tools, further revealed their distinctive genomic makeup. Both short read and long read whole genome sequencing were completed on six of these isolates. In addition to loss of the prot6e gene, the virulence plasmid of each isolate was found to be exceptionally large (86.5 Kb) due to a 28 Kb insertion of S. Typhimurium plasmid sequence that encodes multiple genes of the incF operon. Interrogation of the chromosome sequence data of these isolates using a SNP-based typing tool and MLST both indicated their close genetic relatedness. One additional isolate carrying this plasmid was identified in an in-house collection of S. Enteritidis isolates. Finally, the identification of this unusual plasmid sequence in additional isolates submitted to public repositories of Salmonella sequence data was explored. All these analyses indicated that a very distinctive but rarely reported strain of S. Enteritidis was widely distributed across North America and the United Kingdom with one additional report involving a case from Brazil. With increased use of genetic methods for Salmonella identification, the loss of the prot6e sequence may confound correct identification of this serovar while also potentially altering the mode of transmission to humans given the gene’s role in facilitating propagation of this bacterium in eggs. Accordingly, this strain may present certain challenges with respect to public health investigations. Our studies also suggest this strain is often associated with duck hosts thereby providing a possible mechanism by which this strain has spread over an extensive geographical area.
Highlights
In most countries, including developed nations such as Canada, the United States and those of Europe, Salmonella Enteritidis is recognized as the major Salmonella serotype contributing to human gastroenteritis
Multiple-Locus Variable-Number Tandem-Repeat Analysis (MLVA) subtyping generated 15 types that clustered into two major groups on the Unweighted Pair Group Method with Arithmetic Mean (UPGMA) dendrogram
Cluster 1 (n = 53) included the most common MLVA types 6-8-410-10-1-2 (n = 31) and 6-6-4-11-10-2-2 (n = 9), and seven closely related types represented by 13 isolates
Summary
In most countries, including developed nations such as Canada, the United States and those of Europe, Salmonella Enteritidis is recognized as the major Salmonella serotype contributing to human gastroenteritis. Environmental testing for Salmonella in poultry production facilities is one tool employed in efforts to limit contamination of food by these organisms. To this end traditional culture methods for Salmonella detection are being augmented by more rapid, sensitive and specific molecular genetic based methods
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
