Salmonella

Overview of Salmonella

  • Definition: A genus of bacteria, significant within the family Enterobacteriaceae.

Characteristics of Salmonella

  • Morphology:

    • Gram-negative rods.

    • Non-sporeforming.

  • Lactose Fermentation:

    • Majority of strains do not ferment lactose.

  • Optimal Growth Temperature:

    • Optimal temperature: 37°C; Maximum temperature: 45°C.

  • Growth and Metabolism:

    • Some strains produce hydrogen sulfide (H2S).

    • Can utilize citrate as a carbon source.

  • Natural Habitat:

    • Found in the intestines of various animals including birds, reptiles, farm animals, and humans.

Pathogenicity

  • Human Infection:

    • Causes salmonellosis in humans.

  • Infective Dose:

    • Ranges from 10^7 to 10^9 colony-forming units (cfu). Specific strain S. Eastbourne requires only 1 cfu.

  • Incubation Period:

    • Typically 12 to 14 hours, but can be longer for some serovars.

Taxonomy of Salmonella

  • Species:

    • Primary species includes Salmonella enterica.

  • Subspecies:

    • Six subspecies include:

      • Group I (subsp. enterica): 99% of all human infections.

      • Group II: Salmonella enterica subsp. salamae.

      • Group IIIa: Salmonella enterica subsp. arizonae.

      • Group IIIb: Salmonella enterica subsp. diarizonae.

      • Group IV: Salmonella enterica subsp. houtenae.

      • Group VI: Salmonella enterica subsp. indica.

    • More than 2600 serovars have been identified.

Specific Serovars

  • Salmonella Typhi:

    • A human specialist pathogen that causes typhoid fever.

    • Incubation period: 7 to 23 days.

    • Can lead to systemic infections involving intestines, lymphatics, and blood.

    • Associated with gallstones; 10% of infected individuals are carriers for months, 5% for years.

  • Salmonella Paratyphi:

    • Another human pathogen similar to Typhi but usually less severe.

  • Salmonella Typhimurium:

    • Generalist affecting humans, poultry, swine, and rodents.

    • Causes non-typhoid salmonellosis, with symptoms including nausea, abdominal cramps, vomiting, diarrhea, and blood-tinged stools.

    • Sequelae may include Reiter’s syndrome (joint pains, eye irritation, painful urination, chronic arthritis).

Transmission Modes

Transovarian Transfer

  • Definition: Vertical transfer of Salmonella Enteritidis.

  • Process: Occurs when a hen with an ovarian infection lays eggs containing the pathogen prior to eggshell formation.

Horizontal Transfer

  • Definition: Contamination through penetration of the eggshell.

  • Process: Penetration may occur from contaminated feces or the colonized gut during or after oviposition.

Discussion on Egg Handling Practices

  • Agree-Disagree Section: Engage with an article discussing differing egg refrigeration practices across countries.

  • Chart Purpose: Encourage critical evaluation of egg handling methods in the US vs UK and their implications for public health regarding salmonellosis. Discuss personal opinions on the issue and suggest appropriate handling practices for the Philippines.