Whole genome sequencing provides an unambiguous link between Salmonella Dublin outbreak strain and a historical isolate.

Salmonella enterica subsp. enterica serovar Dublin is an uncommon cause of human salmonellosis; however, a relatively high proportion of cases are associated with invasive disease. The serotype is associated with cattle. A geographically diffuse outbreak of S. Dublin involving nine patients occurred in Ireland in 2013. The source of infection was not identified. Typing of outbreak associated isolates by pulsed-field gel electrophoresis (PFGE) was of limited value because PFGE has limited discriminatory power for S. Dublin. Whole genome sequencing (WGS) showed conclusively that the isolates were closely related to each other, to an apparently unrelated isolate from 2011 and distinct from other isolates that were not readily distinguishable by PFGE.

Application of multiple locus variable number of tandem repeat analysis (MLVA), phage typing and antimicrobial susceptibility testing to subtype Salmonella enterica serovar Typhimurium isolated from pig farms, pork slaughterhouses and meat producing plants in Ireland.

Salmonella enterica subsp. enterica serovar Typhimurium is a common zoonotic pathogen encountered in Irish pigs and the pork industry and its characterisation using highly discriminatory typing methods is necessary for epidemiological studies, outbreak investigation and control. Multiple locus variable number of tandem repeat analysis (MLVA), phage typing and antimicrobial susceptibility testing were applied to characterise 301 S. typhimurium isolates of porcine origin isolated from farms, slaughterhouses and pork meat producing plants in Ireland over a four-year period. 154 MLVA patterns were obtained compared to 19 phage types and 38 AMR patterns, and MLVA was particularly useful for discriminating isolates of the same phage type, e.g. DT104 and DT104b, or isolates that were Untypable or in the category of "react with phage but does not conform to a recognised phage type" (RDNC) by the phage typing method. Cluster analysis of MLVA profiles using a minimum spanning tree (MST) demonstrated two major clusters (I and II), which showed to have a clear association with phage types, cluster I associated to phage types DT104, U302 and DT120 and cluster II associated to DT193 and U288. The results of this present study showed that MLVA is highly discriminatory and permitted the identification of identical profiles among isolates obtained at different points of the pork food chain. The same MLVA profile was observed in some cases among isolates with different phage types. While this can be explained by the fact that some phage types are closely related, it also indicates that combining phage typing and MLVA enhances strain typing of S. typhimurium.

First report of extended-spectrum-beta-lactamase-producing Salmonella enterica serovar Kentucky isolated from poultry in Ireland.

Therapy of invasive human salmonellosis is complicated by increasing antimicrobial resistance. Food animals are the principal source of infection with nontyphoid Salmonella. We report the emergence of broad-spectrum-cephalosporin resistance in Salmonella enterica serovar Kentucky in poultry in Ireland.

Antimicrobial resistance and phage types of human and non-human Salmonella enterica isolates in Ireland, 1998-2003.

Between 1998 and 2003, 5,161 isolates (3,182 human) of Salmonella enterica were received by the National Salmonella Reference Laboratory of Ireland. Serotyping, antimicrobial susceptibility testing and phage typing were performed by standard methods. The number of isolates of S. enterica serovar Typhimurium decreased from 579 (80%) in 1998 to 208 (19%) in 2003, while S. enterica serovar Enteritidis increased from 59 (8%) in 1998 to 219 (20%) in 2003. Definitive (DT) phage types 104 and DT104b accounted for a declining proportion of all Salmonella Typhimurium isolates (from n = 523 [90%] in 1998 to 126 [60%] in 2003). Numbers of Salmonella Enteritidis phage type 4 declined from 50 (85%) in 1998 to 59 (27%) in 2003. Twenty-eight isolates of typhoidal Salmonella were received with a history of recent travel in 17 cases. Resistance to multiple (four or more) antimicrobial agents was related to serotype and, where applicable, phage type, and was common in Salmonella Typhimurium. Salmonella Typhimurium predominated among isolates from cattle and pigs (n = 213 [58%]), while Salmonella Livingstone (n = 327) and S. Kentucky (n = 227) were predominant in isolates from poultry (total n = 554 [43%]). This paper discusses trends, and their implications, in Irish salmonella isolates since the establishment of the Reference Laboratory.