Outbreak of Salmonella enterica serovar Typhimurium phage type DT41 in Danish poultry production

Abstract

Salmonella enterica subspecies enterica serovar Typhimurium (S. Typhimurium) is one of the most prevalent serovars in Europe - where both poultry and poultry related products are common sources of human salmonellosis. Due to efficient control programs, the prevalence of S. Typhimurium in Danish poultry production is very low. Despite this, during the past decades there has been a reoccurring problem with infections with S. Typhimurium phage type DT41 in the Danish poultry production without identifying a clear source. In the end of 2013 and beginning of 2014 an increased isolation of S. Typhimurium DT41 was noted mainly in this production, but also in other samples. To investigate this is in more detail, 47 isolates from egg layers (n=5, 1 flock), broilers (n=33, 13 flocks), broiler breeding flocks and hatches (n=5; 2 flocks and 1 environmental hatchery sample), feed (n=1), poultry slaughter house (n=3, environmental sample and meat) were typed with multi locus variable number of tandem repeat analysis (MLVA) and pulsed-field gel electrophoresis (PFGE) to investigate the epidemiology of the outbreak. Based on PFGE results isolates were divided into four groups (Simpson's index of diversity (DI)=0.24±0.15). Due to the low DI, PFGE was not sufficient to provide information to unravel the outbreak. Based on MLVA typing the DT41 (42/47 isolates) and the RDNC isolates (5/47) were split into nine groups (DI=0.65±0.14). When a maximum divergence at one locus was permitted these could be gathered into four groups. Using this criterion, combined with epidemiological information, a spread of one type from broiler breeders to broilers and further to the poultry slaughter house was plausible. In conclusion, although it could be concluded that a spread within the broiler production pyramid had taken place the source of the sudden increase of S. Typhimurium DT41 remains unclear. To investigate this in more detail, further studies using whole genome sequencing to obtain a higher discriminatory strength and including isolates from a longer period of time and from various sources are in progress.

Use of multiple‐locus variable‐number of tandem repeats analysis (MLVA) to investigate genetic diversity of Salmonella enterica subsp. enterica serovar Typhimurium isolates from human, food, and veterinary sources

“…For all loci, apart from STTR9, there were some strains for which no amplicon was obtained, with the highest number of isolates for STTR10 (Table , Table S1). The discriminatory ability of the different MLVA loci corresponded well with previous investigations (Dimovski et al., ; Löfström, Hintzmann, Sørensen, & Baggesen, ; Wuyts et al., ), showing that STTR5, STTR6, and STTR10 were the loci with highest discriminatory index (DI) whereas a lower DI was observed for STTR3 and STTR9. STTR10 (plasmid borne) has in previous investigations been shown to be absent in many strains, thus being less useful for inclusion in the typing scheme.…”

“…For all loci, apart from STTR9, there were some strains for which no amplicon was obtained, with the highest number of isolates for STTR10 (Table 2, Table S1). The discriminatory ability of the different MLVA loci corresponded well with previous investigations (Dimovski et al, 2014;Löfström, Hintzmann, Sørensen, & Baggesen, 2015;Wuyts et al, 2013), showing that STTR5, STTR6, and STTR10…”

Observations on the distribution and control ofSalmonellain commercial duck hatcheries in the UK

“…In this case, some breeding flocks related to this hatchery were infected with this phage type, but eggs from these flocks were also hatched in hatchery two, where no S. Typhimurium DT41 was isolated (data not shown). S. Typhimurium DT41 is normally associated with wild birds, particularly water fowl (Pennycott et al, 2006) but a spike in the prevalence of this serotype has been observed in broilers and broiler breeders in Denmark in recent years (Löfström et al, 2015). In this study, the tray wash area and waste/processing areas had the largest probability of being contaminated by Salmonella.…”

Prevalence and molecular characterization ofSalmonella entericaisolates throughout an integrated broiler supply chain in China

“…Contamination of chicken or chicken meat may occur throughout the whole production chain and some important risk factors for contamination at each stage of this process have been identified. The risk factors include inadequate cleaning and disinfection of broiler rearing houses, contamination of feed, and chicken production process; these factors can be a significant source of pathogen contamination between carcasses [5]. To our knowledge, S. enterica always exists in the alimentary tract and reproductive system of carrier chickens.…”