Identification of Bovine Genotypes Conferring Diminished Susceptibility to Salmonellosis and Colonization bySalmonellaandE. coliO157:H7
Authors: Anderson Kristi L. , Ramsey Duane K. , Day Tim A. , Carlson Steve A. 
Published: July 2020

SalmonellaandE. coliO157:H7 are two of the most important problems for the beef industry. Cattle can develop salmonellosis and persistently harborSalmonella, or they can asymptomatically shedSalmonellaand/orE. coliO157:H7 resulting in contamination of the hide and carcass surfaces during processing. Additionally,Salmonellainfiltrates lymph nodes that get incorporated into ground beef. In this study, we investigated the possibility of identifying cattle with reduced susceptibility to one or both of these infections. Empirical observations from previous studies suggested that a diminished susceptibility was possible in amelanotic cattle,i.e., cattle bearing themcr1/mcr1genotype and lacking overt black pigmentation. By searching for single nucleotide polymorphisms (SNP) present in the 34 genes encoding theSalmonellainteractome, we identified a SNP that was consistently present in amelanotic cattle with diminished susceptibility toSalmonella. Specifically, we used anex vivoassay to screen 500 cattle blood samples for the diminished ability ofSalmonellato penetrate peripheral leukocytes. DiminishedSalmonellapenetration was observed in 150 of these blood samples and 147 of these samples harbored two alleles bearing a SNP that introduces a miRNA cleavage site (bta-let-7b) in the 3’UTR of thebsynJ1gene, which we designate as theSYNJ1/SNYJ1genotype. Furtherex vivostudies revealed a decreased expression ofSYNJ1in leukocytes bearing theSYNJ1/SNYJ1genotype.In vivoexperimental challenge studies revealed a diminished susceptibility to salmonellosis in cattle with theSYNJ1/SNYJ1::mcr1/mcr1genotype. Additionalin vivochallenge studies revealed thatSYNJ1/SNYJ1::mcr1/mcr1cattle have a decreased susceptibility to lymph node infiltration by twoSalmonellaserotypes (S. Anatum andS. Montevideo) implicated in this lymph node problem, and a decreased susceptibility toE. coliO157:H7 colonization of the recto-anal junction. A field study revealed that theSYNJ1/SNYJ1::mcr1/mcr1genotype was five times more prevalent, when compared to theSYNJ1/synj1::mcr1/mcr1andsynj1/ synj1::mcr1/mcr1genotypes, inSalmonella-free lymph nodes. Small-scale genetic surveys revealed that theSYNJ1/SNYJ1genotype was present in the followingmcr1/mcr1breeds: Akaushi, Barzona, Braunvieh, Hereford, Piedmontese, Red and White Holsteins, Red Angus, Red Poll, Shorthorn, Simmental (Red), and Tarentaise. Studies using the aforementionedex vivopenetration assay, which putatively predicts the diminished susceptibility phenotype, revealed that the penetrance of the diminished susceptibility is >99% inSYNJ1/SNYJ1::mcr1/mcr1cattle but only ∼1% inSYNJ1/SNYJ1cattle with at least oneMCR1allele. Further studies with theex vivoassay revealed that three additional SNPs are part of a genotype conferring diminished susceptibility to a broad array ofSalmonellaserotypes commonly associated with cattle. In summary, the studies presented herein reveal a bovine genotype associated with decreased susceptibility toSalmonellaandE. coliO157:H7. PSR Genetics LLC holds a U.S. patent on testing for theSYNJ1/SNYJ1genotype (patent number 9,049,848) while the three complementary SNPs are under further investigation.