Salmonella spp. are a group of bacteria that live in the intestines of humans and animals and are one of the most common causes of foodborne illness worldwide. People are usually infected by eating contaminated food, such as undercooked chicken, eggs, or meat, or by drinking unsafe water. The infection, called salmonellosis, typically causes diarrhoea, stomach cramps, fever, nausea, and vomiting. While most cases are mild, the bacteria can sometimes spread into the bloodstream, leading to more severe infections that require medical care (Knodler & Elfenbein, 2019).

In the gut, a healthy balance of microbes usually helps prevent Salmonella from establishing itself. However, when this balance is disrupted—for example, after antibiotic use—the bacteria can invade more easily. Interestingly, Salmonella has evolved ways to exploit gut inflammation, giving it an advantage over helpful bacteria. With more than 2,500 serotypes, including S. Typhimurium and S. Enteritidis, Salmonella remains a primary global health concern. Some types, like S. Typhi, cause typhoid fever, which still affects millions in parts of Africa and Asia (Baldridge & Serezani, 2022; Wotzka et al., 2020).

✔️ What it is: A group of bacteria that cause foodborne illness and, in some cases, typhoid fever.

✔️ Where it’s found: Contaminated food (especially chicken, eggs, meat), unpasteurised milk, and unsafe water.

✔️ Common symptoms: Diarrhoea, stomach cramps, fever, nausea, and vomiting.

✔️ How it spreads: Through eating/drinking contaminated food or water, or contact with infected animals/humans.

✔️ Global impact: Among the leading causes of bacterial gastroenteritis worldwide.

✔️ High-risk groups: Infants, the elderly, pregnant women, and people with weakened immune systems.

✔️ Complications: Can spread into the bloodstream, causing severe infection; S. Typhi causes typhoid fever.

✔️ Prevention: Proper food handling, thorough cooking, safe water, and good hygiene practices.

✔️ Gut health link: A balanced gut microbiome usually protects against Salmonella, but disruption (e.g., after antibiotics) can increase risk.

✔️ Why it matters in SA: Food safety and water quality issues make Salmonella a continuing public health concern.

The body’s immune response to Salmonella spp. involves both innate and adaptive mechanisms. When Salmonella enters through contaminated food or water, it first encounters the innate immune system. Intestinal epithelial cells and resident macrophages detect the bacteria through pattern recognition receptors (PRRs) such as Toll-like receptors, triggering the release of inflammatory cytokines like IL-1β, IL-6, and TNF-α (Furci et al., 2019). Neutrophils are rapidly recruited to the site of infection, helping to contain bacterial spread (Stecher, 2021). The gut microbiota also plays a role by providing colonisation resistance — competing with Salmonella for nutrients and limiting its ability to adhere and invade epithelial cells (Mendes et al., 2024).

On the adaptive side, dendritic cells present Salmonella antigens to T and B lymphocytes. CD4+ T cells stimulate further inflammatory responses, while CD8+ T cells can kill infected host cells (Furci et al., 2019). Antibody production, particularly secretory IgA in the gut mucosa, helps neutralise the bacteria and prevent reinfection (Mendes et al., 2024). However, Salmonella has evolved strategies to evade immunity, such as surviving inside macrophages by altering the phagosomal environment (Klein et al., 2020). This balance between immune activation and bacterial evasion often determines whether infection results in asymptomatic carriage, self-limiting gastroenteritis, or systemic disease like typhoid fever (Stecher, 2021).

Gastrointestinal Symptoms

Diarrhoea — often watery, sometimes bloody

Abdominal cramps — sharp or cramping pain in the lower abdomen

Nausea and vomiting — common early symptoms

Fever and chills — usually low-grade but can become higher in severe cases

Systemic Symptoms (if infection spreads beyond the gut)

Headache and muscle aches — due to systemic inflammation

Fatigue and malaise — overall weakness and tiredness

Dehydration — from fluid loss, leading to dizziness, dry mouth, and reduced urination

Sepsis (rare but serious) — high fever, confusion, rapid heartbeat when bacteria spread to the bloodstream

Long-Term or Complication-Linked Symptoms

Reactive arthritis (Reiter’s syndrome) — joint pain, eye irritation, and painful urination that may occur weeks after infection

Chronic carrier state — some individuals, especially after Salmonella Typhi infection, can carry bacteria without symptoms but still spread it.

⚠️ Most infections are self-limiting (4–7 days), but severe cases, especially in young children, the elderly, or immunocompromised individuals, can progress to systemic illness that requires medical treatment.

In South Africa, Salmonella, particularly non-typhoidal serovars, is a significant contributor to gastrointestinal disease, especially in children. A recent pediatric study found that Salmonella spp. accounted for about 5% of gastroenteritis cases in South African children, highlighting its role among key bacterial agents alongside Escherichia coli and Clostridioides difficile (Mwangi et al., 2023). Outbreaks of foodborne Salmonella, such as those linked to Salmonella Heidelberg in school feeding programs, further emphasise the acute risk posed when food safety is compromised (Lekalakala et al., 2012).

South Africa also faces both gastrointestinal and systemic presentations of Salmonella infection. Salmonella Enteritidis, one of the most common non-typhoidal serovars, is associated not only with gastroenteritis but also with invasive infections, particularly in individuals with weakened immune systems (Musyoka et al., 2023). The increasing prevalence of antimicrobial-resistant strains of S. Enteritidis raises serious concerns for effective treatment and prevention of salmonellosis in the region (Musyoka et al., 2023).

To minimise the risk of Salmonella colonisation:

✅ Maintain a diverse gut microbiome — eating fibre-rich foods, fermented foods (yoghurt, kefir, kimchi), and prebiotics helps beneficial microbes thrive, making it harder for Salmonella to establish.

✅ Food safety — proper cooking of poultry, eggs, and meat; washing fruits and vegetables; and avoiding cross-contamination in the kitchen reduces exposure.

✅ Hydration and electrolyte balance — if exposed, maintaining hydration supports gut barrier function and resilience.

✅ Limit unnecessary antibiotics — overuse can disrupt the microbiome and give Salmonella an advantage.

✅ Strengthen immunity — through sleep, stress management, vaccination (for typhoidal strains in high-risk settings), and balanced nutrition.