Salmonella enterica serovar Typhimurium Infection Models

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a Gram-negative rod of the Enterobacteriaceae and one of the leading causes of nontyphoidal salmonellosis. It spreads through contaminated food (such as undercooked poultry, eggs, beef, and produce) and through contact with birds, reptiles, and their feces. In healthy people, it typically causes a self-limiting gastroenteritis of diarrhea, fever, and abdominal cramps, but it can invade the bloodstream and cause severe, life-threatening disease in young children, older adults, and people with weakened immunity.

Nontyphoidal Salmonella is among the most common causes of foodborne illness, responsible for well over a million infections a year in the United States alone, and invasive nontyphoidal Salmonella is a major cause of bloodstream infection and death in sub-Saharan Africa. The CDC classifies drug-resistant nontyphoidal Salmonella as a serious threat. S. Typhimurium is also a long-established model organism for enteric and systemic bacterial infection, which makes it a well-characterized challenge for preclinical work. TransPharm Preclinical Solutions evaluates candidates against S. Typhimurium in a gastrointestinal infection and peritonitis model and produces the quantitative burden, clinical, and survival data a development program needs.

The scientific problem in an S. Typhimurium study is that robust intestinal infection depends on the state of the host’s microbiota. Two further choices shape the study. The first is strain: a well-characterized reference isolate supports colonization- and burden-based readouts, while a multidrug-resistant or extended-spectrum-β-lactamase-producing clinical isolate is the relevant challenge for a candidate positioned against resistant disease. The second is host: susceptibility to systemic spread of Salmonella is strongly influenced by mouse genetic background, so the host strain is chosen to fit whether the question is enteric colonization or invasive, disseminated disease.

TransPharm Preclinical Solutions maintains an on-site library of hundreds of validated pathogens and can source or validate characterized S. Typhimurium isolates, including defined resistant phenotypes, to a program’s specifications.

Every study parameter is configurable to the scientific question: challenge strain, host species and strain, microbiota-disruption regimen, route of administration, comparator agents, and dosing schedule. The core readouts pair quantitative bacterial burden with clinical measures of disease.

The following are available as add-ons to any study:

• Pharmacokinetic profiling and PK/PD analysis
• Blood chemistry
• Additional tissue harvests
• Histopathology

The gastrointestinal model reproduces S. Typhimurium infection as it arises clinically: the resident microbiota is first disrupted, then the animal is challenged and colonization and disease are allowed to develop. Animals are challenged by oral gavage. Test article may be administered orally or perirectally, by subcutaneous, intravenous, or intraperitoneal injection, or via diet or drinking water – the range of routes suiting both systemic candidates and gut-restricted agents. Endpoints include mortality tracking, clinical observations, weight tracking, and CFU burden in feces, organs, and/or blood – the organ and blood measures capturing dissemination beyond the gut. Validated in mice. Validated S. Typhimurium isolate: CDC 6516-60 (equivalent to ATCC 14028), a whole-genome-sequenced reference strain originally isolated from poultry.

In vitro susceptibility testing complements the in vivo model. S. Typhimurium MIC is determined by broth or agar dilution per CLSI, and can be paired with MBC, time-kill, and checkerboard analysis to characterize a candidate against susceptible and resistant isolates – including against the cephalosporin and fluoroquinolone resistance that matters most clinically.

Most nontyphoidal Salmonella infections resolve without antibiotics, so resistance matters most where treatment is essential: severe gastroenteritis and invasive disease in children, older adults, and immunocompromised patients. The drugs that treat those infections (ceftriaxone, ciprofloxacin, and ampicillin) are precisely the ones resistance now threatens. S. Typhimurium carries a well-documented history of multidrug resistance, most famously the penta-resistant DT104 lineage (resistant to ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline), and clinically critical resistances continue to spread: fluoroquinolone resistance through gyrA/parC mutations and plasmid-borne qnr genes, and third-generation cephalosporin resistance through ESBL and AmpC β-lactamases. Much of this resistance is driven by antimicrobial use in food animals and moves to people through the food supply. Because the resistance profile of the challenge strain determines whether a study speaks to treatable or hard-to-treat disease, strain selection – susceptible reference versus defined resistant isolate – is central to an S. Typhimurium efficacy program.