Salmonella enterica is a Gram-negative, facultatively anaerobic rod belonging to the Enterobacteriaceae family. Over 2,500 serovars have been identified through the Kauffmann-White scheme, which classifies strains based on somatic (O), flagellar (H), and capsular (Vi) antigens. Common food-associated serovars include S. Enteritidis (eggs, poultry), S. Typhimurium (multiple sources), and S. Newport (produce, beef). The genus is broadly divided into typhoidal serovars (S. Typhi, S. Paratyphi) causing typhoid fever and non-typhoidal serovars responsible for self-limiting gastroenteritis.
The infectious dose for non-typhoidal Salmonella ranges from 10³ to 10⁶ CFU depending on serovar, food matrix, and host susceptibility. After ingestion, Salmonella invades intestinal epithelial cells via a type III secretion system, triggering inflammation and diarrhea. Sources include raw and undercooked poultry, eggs, dairy, fresh produce, and contaminated feed. Cross-contamination during processing and handling is a major contributing factor in outbreaks. The bacterium can form biofilms on food contact surfaces, enhancing its persistence in processing environments.
Detection of Salmonella follows a multi-step cultural protocol: pre-enrichment in buffered peptone water, selective enrichment in Rappaport-Vassiliadis or tetrathionate broth, plating on selective agars (XLD, Hektoen, SS agar), and confirmation by biochemical tests (TSI, urea, ONPG) and serotyping. Rapid methods include PCR (invA gene target), real-time PCR, ELISA, and whole-genome sequencing for outbreak investigation and source tracking. Serotyping remains essential for epidemiological surveillance and is increasingly performed by molecular methods targeting O and H antigen genes.
Control measures include proper cooking (minimum internal temperature of 74°C for poultry), pasteurization of eggs and dairy, HACCP-based interventions in slaughter and processing, irradiation of spices, and good agricultural practices for produce. Vaccination of poultry flocks has been effective in reducing S. Enteritidis prevalence in eggs. Effective sanitation of food contact surfaces and separation of raw and cooked products remain critical for preventing cross-contamination. Control of Salmonella is integrated into HACCP plans in poultry and egg processing. Along with Escherichia coli, Listeria monocytogenes, Campylobacter, and Clostridium species, it is one of the major foodborne pathogens targeted by food safety management systems.
