Relationship between Salmonella infection, shedding and serology in fattening pigs in low–moderate prevalence areas

Abstract

Salmonella is a major foodborne pathogen causing important zoonosis worldwide. Pigs asymptomatically infected in mesenteric lymph nodes (MLN) can be intermittent shedders of the pathogen through faeces, being considered a major source of human infections. European baseline studies of fattening pig salmonellosis are based on Salmonella detection in MLN. This work studies the relationship between Salmonella infection in MLN and intestinal content (IC) shedding at slaughter and the relationship between the presence of the pathogen and the serologic status at farm level. Mean Salmonella prevalence in the selected pigs (vertically integrated production system of Navarra, Spain) was 7.2% in MLN, 8.4% in IC and 9.6% in serum samples. In this low-moderate prevalence context, poor concordance was found between MLN infection and shedding at slaughter and between bacteriology and serology. In fact, most of shedders were found uninfected in MLN (83%) or carrying different Salmonella strains in MLN and in IC (90%). The most prevalent Salmonellae were Typhimurium resistant to ACSSuT ± Nx or ASSuT antibiotic families, more frequently found invading the MLN (70%) than in IC (33.9%). Multivariable analysis revealed that risk factors associated with the presence of Salmonella in MLN or in IC were different, mainly related either to good hygiene practices or to water and feed control, respectively. Overall, in this prevalence context, detection of Salmonella in MLN is an unreliable predictor of faecal shedding at abattoir, indicating that subclinical infections in fattening pigs MLN could have limited relevance in the IC shedding.

Salmonella Infection in Mesenteric Lymph Nodes of Breeding Sows

“…The research was performed in Navarra, a region in Northern Spain with moderate-low prevalence of Salmonella in fattening pigs (San Román et al, 2018). In this context, a total of 65,308 breeding sows kept on 763 farms were registered in 2014 (INTIA, personal communication).…”

“…In some EU countries, serological diagnosis is considered an alternative in Salmonella control programs in fattening pigs (Mousing et al, 1997;Merle et al, 2011;Meroc et al, 2012). Nevertheless, no correlation was observed between serology and the presence of Salmonella in MLN or fecal samples of these animals (San Román et al, 2018).…”

Salmonella persisters promote the spread of antibiotic resistance plasmids in the gut

“…Salmonella enterica and E. coli strains harbor numerous resistance plasmids 13,14 and different strains frequently colonize the same host [15][16][17][18][19] . High cell densities in the gut lumen allows high rates of plasmid transfer within and between species [20][21][22] .…”

“…High cell densities in the gut lumen allows high rates of plasmid transfer within and between species [20][21][22] . S.Tm strains can colonize the gut lumen and survive within tissues of the host for prolonged periods of time [5][6][7][15][16][17]23 . In the absence of suitable resistance genes, the gut luminal S.Tm population is eliminated by antibiotics within a few hours, while tissue-associated S.Tm persister cells survive >10 days [5][6][7][8]24 (supplementary discussion A).…”

“…There can be two different Salmonella strains within the same host, one within lymphoid tissues (e.g. mesenteric lymph nodes) and the other in the intestinal content 17 . This is also in line with the isolation of Salmonella spp.…”