Role of systemic infection, cross contaminations and super‐shedders in Salmonella carrier state in chicken

Abstract

Carriage of Salmonella is often associated with a high level of bacterial excretion and generally occurs after a short systemic infection. However, we do not know whether this systemic infection is required or whether the carrier-state corresponds to continuous reinfection or real persistence in caecal tissue. The use of a Salmonella Enteritidis bamB mutant demonstrated that a carrier-state could be obtained in chicken in the absence of systemic infection. The development of a new infection model in isolator showed that a marked decrease in animal reinfection and host-to-host transmission between chicks led to a heterogeneity of S. Enteritidis excretion and colonization contrary to what was observed in cages. This heterogeneity of infection was characterized by the presence of super-shedders, which constantly disseminated Salmonella to the low-shedder chicks, mainly through airborne movements of contaminated dust particles. The presence of super-shedders, in the absence of host-to-host transmission, demonstrated that constant reinfection was not required to induce a carrier-state. Finally, our results suggest that low-shedder chicks do not have a higher capability to destroy Salmonella but instead can block initial Salmonella colonization. This new paradigm opens new avenues to improve understanding of the carrier-state mechanisms and to define new strategies to control Salmonella infections.© 2018 Society for Applied Microbiology and John Wiley & Sons Ltd.

Impact of Host Genetics on Caecal Microbiota Composition and on Salmonella Carriage in Chicken

“…Using a model of Salmonella infection in isolators limiting animal-animal recontaminations and animal reinfection and thus homogenisation of individual Salmonella carriage [1], we con rm the existence of variability linked to genetics and microbiota composition. We evidenced gut microbiota differences associated to both the genetic line (N vs 6 1 ) and individual Salmonella carriage status (high vs. low ISC carriers).…”

“…They were immediately transferred to the PFIE unit (Plateforme d'Infectiologie Expérimentale, INRA, Nouzilly, France) where they were reared together in battery cages. On day 7, each chick was orally infected with Salmonellaenterica Enteritidis (Strain 775 [LA5 Nal20Sm500], 5.10 4 cfu/0.2 mL/chick) and animals were transferred into four isolators to decrease oro-faecal recontaminations as described previously [1]. Two isolators contained chicks from line N and two other isolators contained chicks from line 6 1 , with 30 birds per isolator.…”

“…In adult chickens, Salmonella enterica Enteritidis (SE) does not induce symptoms and can stay in the organism for a long time [1]. Carrier animals excrete the bacteria in the environment, thus increasing the bacteria propagation and facilitating the contamination of all animals.…”

“…This recontamination probably leads to a homogenization of Salmonella carriage in chicken ocks. The use of isolators, strongly reducing this recontamination, actually led to a much increased variation among birds in the experimental White Leghorn line PA12 [1], allowing the description of three categories of birds according to their shedding: super-, intermediate-and low-shedders. These isolators allow a control of the air purity and limit faecal-oral recontaminations between birds by the use of grids on the oor and decontamination of faecal drops.…”

“…In this study, we investigated the combined in uence of host genetic variations and gut microbiota composition on caecal Salmonella Enteritidis (SE) load. Using the chicken N and 6 1 inbred lines, we studied the impact of genetics on both the Salmonella carriage and microbiota composition at the individual level, using the isolator model, which highly decreases the exchanges of gut microbiota between animals [1]. We infected 240 animals with Salmonella Enteritidis at 7 days post hatching.…”