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Genetic characteristics:

Serovar Stanley has been found to be polyphyletic with two lineages identified and two stand-alone singletons that do not cluster with any other Salmonella Stanley isolates. Hendriksen et al. confirmed that multiple plasmid lineages containing bla_CMY-2 gene, which encodes extended-spectrum cephalosporin resistance, were present in serovar Stanley isolates from central Thailand. Serovar Stanley isolates in a Chinese study showed resistance to six antimicrobials—ampicillin, ciprofloxacin, cefotaxime, azithromycin, trimethoprim/sulfamethoxazole, and chloramphenicol—and harbored 14 resistance genes across five classes: β-lactams (bla_TEM-1B, bla_OXA-1, bla_DHA-1), quinolones (qnrB4, aac(6')-Ib-cr), macrolides (mph(A), mph(E), msr(E)), folate pathway inhibitors (sul1, sul2, dfrA14), and chloramphenicol (floR, catA2, catB3). A T57S mutation in parC’s quinolone resistance-determining region was detected, along with three plasmid replicons (IncHI2/IncHI2A, IncR, IncN) and three MGEs. Among 42 virulence genes, 25 were secretion/transport-related, 10 encoded fimbrial adherence factors, and only the inv gene in SPI-1 was linked to invasiveness, with no typhoid toxin genes identified.

A Taiwanese study revealed that genetically diverse Salmonella Typhimurium and clonally disseminated Salmonella Stanley elicited distinct immune responses, with serovar Stanley showing higher phagocytosis rates, reduced intracellular survival, elevated reactive oxygen species (ROS) production, and increased expression of the pro-inflammatory cytokine IL-1β when exposed to dead bacterial cells. These differences in host immune interaction may contribute to the lower prevalence of Salmonella Stanley compared to Salmonella Typhimurium. Rao and Chauhan studied pathogenesis of serovar Stanley infection in experimental chicks and found after oral exposure, serovar Stanley could be found in different organs at varying time periods: present in the duodenum between 6 hours and 5 days post-infection, in the caecum from 12 hours to 9 days, and detectable in the liver, spleen and bloodstream between 24 hours and 7 days. The development of infection resistance was only observed in animals older than 10 days, with no significant protection seen in those 6 days old or younger.

Animal reservoir: Swine is the reservoir of serovar Stanley. According to the metadata from NCBI PD, this serovar was also isolated from other animals such as fish (Labeo rohita), snake (Naja siamensis), and frog.

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