Salmonella Study Notes

Salmonella Overview

  • Family: Enterobacteriaceae

  • Characteristics:

    • Motile, Gram-negative, facultative anaerobes

    • Non-lactose fermenting

    • Resistant to bile salts

Classification and Taxonomy

  • Traditionally classified by serotyping and biochemical assays.

  • Over 2400 O-serotypes (Kauffman-White schema).

  • Currently, mostly recognized as:

    • Salmonella enterica (6 subspecies)

    • S. bongori

  • Host range divides serotypes into host-adapted and ubiquitous.

Diseases Caused

  • Salmonella infections include:

    • Enteritis (gastroenteritis)

    • Septicemia

    • Enteric fever (typhoid and paratyphoid fevers)

    • Asymptomatic carriage

Transmission

  • Major transmission routes:

    • Ingestion of contaminated food (especially poultry, eggs, dairy).

    • Direct fecal-oral spread, especially in children.

At-Risk Groups

  • Children, elderly, patients with reduced gastric acids, and individuals with compromised immune systems (e.g., AIDS).

  • S. typhi: foreign travelers or those exposed to carriers.

Geographic & Seasonal Distribution

  • Worldwide, with higher incidence in warmer months.

Control Measures

  • Focus on proper food preparation, refrigeration, and hygiene.

  • Symptomatic treatment instead of antibiotics for enteritis.

Virulence Factors

  • Use of Type III secretion systems (T3SS):

    • T3SS-1: Promotes entry into epithelial cells.

    • T3SS-2: Aids survival within macrophages.

  • Additional virulence factors include:

    • Flagella

    • Capsule (e.g., S. typhi)

    • Adhesins and iron-capturing ability.

Mechanism of Infection

  • Salmonella survives stomach acidity, enters epithelium via M cells, and disseminates through macrophages.

  • Induces inflammatory responses, leading to diarrhea and systemic illness.

Treatment and Prevention

  • Enteritis:

    • Maintain food hygiene; antibiotics not recommended for treatment.

  • Enteric fever:

    • Ensure food/water hygiene, treat carriers, and vaccination for travelers.

Summary

  • Salmonella infections are zoonotic and primarily transmitted via the oral-faecal route.

  • T3SS play a critical role in virulence.

  • S. typhi, unique to humans, causes typhoid fever and can lead to chronic carriage and community spread.