Microbiology · MU Plovdiv

26. Salmonella. General characteristics – morphology, biology, classification, antigenic structure, pathogenic factors, diseases, microbiological diagnosis. Dysentery (Shigella spp.). Characteristics and microbiological diagnosis. Pseudomonas. Morphology, biology, pathogenic factors. Diseases. Microbiological diagnosis. Therapeutical problems.

Inside: 19 sections · 14 labelled pictures · 4 tables · 30 flashcards · 6 min

Topic 26 of 41 in the MU Plovdiv syllabus for Microbiology (Dental Medicine, Year 3). The free AceMed note covers it in 19 sections, about 585 words (6 min of reading), with 30 flashcards.

In this note

  1. Genus Salmonella – Causative agents of Typhoid and Paratyphoid Diseases
  2. I. General Characteristics
  3. II. Classification and Types
  4. III. Virulence Factors
  5. IV. Transmission and Epidemiology
  6. V. Clinical Features and Diseases
  7. VI. Laboratory Diagnosis
  8. VII. Treatment
  9. VIII. Prevention and Control
  10. Genus Salmonella – Causative Agents of Food Toxicoinfections
  11. General Characteristics
  12. Virulence Factors
  13. Epidemiology
  14. Pathogenesis (Food Toxicoinfection Type)
  15. Clinical Features
  16. Laboratory Diagnosis
  17. Treatment
  18. Prevention
  19. Differentiation from Typhoidal Salmonella

I. General Characteristics

  • Family: Enterobacteriaceae
  • Gram Staining: Gram-negative rods
  • Motility: Motile (peritrichous flagella)
  • Spores: Non-spore forming
  • Capsule: No microcapsule usually (S. Typhi has one)
  • Pili: Present – used for adhesion
  • Oxygen Requirement: Facultative anaerobes
  • Biochemical:
  • Oxidase (-)
  • Lactose (-)
  • H2S (+) (except S. Paratyphi A)
  • Media:
  • Non-fastidious – grow on MacConkey agar, Deoxycholate Citrate Agar (DCA)
  • Produce rounded, transparent colonies on MacConkey agar
  • On DCA – black-centered colonies (due to H2S production)
  • Serologic Classification:
  • Based on O (somatic), H (flagellar), and Vi (capsular) antigens

II. Classification and Types

  • Species:
  • Salmonella enterica
  • Salmonella bongori
  • Pathogenic Serotypes:
  • S. Typhi – Human-specific pathogen
  • S. Paratyphi A, B, C – Milder illness
  • S. Enteritidis, S. Typhimurium – Cause toxicoinfections and gastroenteritis

IV. Transmission and Epidemiology

  • Transmission Route: Faeco-oral (contaminated food/water)
  • Reservoirs:
  • S. Typhi/Paratyphi – Humans only
  • S. Enteritidis/Typhimurium – Farm animals, poultry, eggs, unpasteurised milk
  • Risk Factors: Poor sanitation, unhygienic food practice

V. Clinical Features and Diseases

1. Typhoid Fever (Enteric Fever)

  • Caused by: S. Typhi
  • Incubation: 1–3 weeksSymptoms:
  • Step-ladder fever pattern
  • Abdominal pain
  • Diarrhoea or constipation
  • Rose spots on abdomen (rash)
  • Hepatosplenomegaly
  • Bradycardia (Faget sign)
  • Delirium (“typhoid state”)

2. Paratyphoid Fever

  • Caused by: S. Paratyphi A/B/C
  • Similar to typhoid but generally milder because it doesn’t penetrate the basal membrane.

4. Septicaemia

  • S. Choleraesuis, S. Typhimurium in immunocompromised
  • May lead to localised infections (bones, joints, lungs

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