55. Genus Salmonella. Causative agents of food toxicoinfections.
Covers the general features of the genus Salmonella, including its Gram-negative morphology, growth on selective media and its place in Enterobacteriaceae. It then sets out virulence factors in a table, the epidemiology and the invasive, non-toxin-mediated mechanism of non-typhoidal strains such as S. Enteritidis and S. Typhimurium. Clinical features, culture and serological diagnosis, supportive and antibiotic treatment, and prevention follow. A final table contrasts non-typhoidal with typhoidal Salmonella.
Topic 55 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 10 sections, about 258 words (3 min of reading), with 15 flashcards.
In this note
Genus Salmonella – Causative Agents of Food Toxicoinfections
General Characteristics
Virulence Factors
Epidemiology
Pathogenesis (Food Toxicoinfection Type)
Clinical Features
Laboratory Diagnosis
Treatment
Prevention
Differentiation from Typhoidal Salmonella
General Characteristics
Gram-negative, rod-shaped (bacilli)
Motile – peritrichous flagella (all around cell)
Facultative anaerobes
Non-spore forming
Oxidase-negative, Catalase-positive
Lactose non-fermenting, H₂S producing (→ black colonies on DCA)
Belongs to family Enterobacteriaceae
Grow well on MacConkey agar, XLD, and Deoxycholate Citrate Agar (DCA)
Epidemiology
Worldwide, especially in developing countries
Main source: contaminated food → poultry, eggs, raw milk, undercooked meat
Zoonotic – reservoir: farm animals and birds
Transmitted via alimentary route
Pathogenesis (Food Toxicoinfection Type)
Caused by non-typhoidal Salmonella:
S. Enteritidis
S. Typhimurium
Mechanism:
3. Bacteria ingested via contaminated food
4. Survive stomach acidity and reach small intestine
5. Invade intestinal epithelial cells → mainly M cells over Peyer’s patches
