Prophylactic administration of vector-encoded porcine granulocyte-colony stimulating factor reduces Salmonella shedding,tonsil colonization,& microbiota alterations of the gastrointestinal tract in Salmonella-challenged swine

Authors: Bearson, Shawn; Bearson, Bradley - Brad; Loving, Crystal; Allen, Heather; LEE, INSOO - Hannam University; MADSON, DARIN - Iowa State University; Kehrli Jr, Marcus

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2016
Publication Date: 8/25/2016
Citation: Bearson, S.M., Bearson, B.L., Loving, C.L., Allen, H.K., Lee, I., Madson, D., Kehrli Jr, M.E. 2016. Prophylactic administration of vector-encoded porcine granulocyte-colony stimulating factor reduces Salmonella shedding, tonsil colonization, and microbiota alterations of the gastrointestinal tract in Salmonella-challenged swine. Frontiers in Veterinary Science. 3:66. doi: 10.3389/fvets.2016.00066.

Interpretive Summary: Salmonella is a human foodborne bacterium that can live in animals such as pigs, poultry and cattle without causing disease symptoms. Efforts to reduce Salmonella carriage in food animals are hindered by the existence of over 2,500 serovars of Salmonella. To develop an intervention strategy that is non-specific yet effective against these diverse Salmonella serovars, we boosted the immune response of a group of pigs by giving them a porcine-derived product that would increase the immune cells (neutrophils) that combat Salmonella. Pigs that received the engineered vector expressing porcine granulocyte-colony stimulating factor (Ad5-G-CSF) prior to Salmonella exposure had reduced Salmonella fecal shedding and decreased Salmonella counts in their tissues compared to the pigs that received the vector only (Ad5-empty). Furthermore, the Ad5-G-CSF pigs had less Salmonella-induced disturbance of the bacteria that reside in their intestinal tract (microbiota). Collectively, these data suggest that delivery of a targeted immunostimulant to enhance innate immunity may be a strategy to reduce Salmonella colonization, potentially during periods of immunological and animal production stress such as farrowing, weaning, and transportation.

Technical Abstract: Salmonella colonization of food animals is a concern for animal health and public health as a food safety risk. Various obstacles impede the effort to reduce asymptomatic Salmonella carriage in food animals, including the existence of numerous serovars and the ubiquitous nature of Salmonella. To develop an intervention strategy that is non-specific yet effective against diverse Salmonella serovars, we explored the prophylactic use of a cytokine to decrease Salmonella in swine by boosting the host’s innate immune system. Granulocyte-colony stimulating factor (G-CSF) is the major cytokine regulating the production, differentiation, function, and survival of neutrophils. Neutrophils play a critical role in the response to Salmonella; therefore, we evaluated the vectored-delivery of porcine G-CSF as a prophylactic to reduce Salmonella in pigs. Crossbred pigs, five weeks of age, were intramuscularly injected with a replication-defective human adenovirus (Ad5) engineered to express porcine G-CSF (Ad5-G-CSF, n=9). Control pigs received the same Ad5 vector lacking the gene encoding G-CSF (Ad5-empty, n=7). Four days later, all pigs (n=16) were intranasally inoculated with 1 x 107 CFU of Salmonella enterica serovar Typhimurium UK1. At 2 and 3 days post-challenge with Salmonella, Ad5-G-CSF treated pigs shed significantly less Salmonella (approximately 103 CFU/g) in their feces than Ad5-empty treated pigs (approximately 104-105 CFU/g; P less than 0.05). A significant 4-log reduction in tonsil colonization was also observed in the Ad5-G-CSF treated pigs at 7 days post-challenge (P less than 0.05). In the gastrointestinal tract, the Peyer’s patch region of the ileum exhibited a significant 0.5 log reduction in colonization in the Ad5-G-CSF treated pigs (P less than 0.05). The microbiota of all challenged pigs was assessed by sequencing and analyzing the V1-V3 region of the 16S rRNA gene from fecal DNA samples. The microbial community structure of Salmonella-challenged pigs was less disturbed at 7 days post-challenge in Ad5-G-CSF treated pigs when compared to the Ad5-empty treated pigs. This suggests that Ad5-G-CSF administration mitigated changes in the microbial community structure caused by Salmonella challenge. Collectively, these data suggest that delivery of a targeted immunostimulant to enhance neutropoiesis may be a strategy to reduce Salmonella colonization, potentially during periods of immunological stress.