Lecture Notes: Salmonella

Overview of Salmonella

• Species: Over 2,500 species divided into groups.
• Common Associations: Often linked to raw chicken or eggs.
• Exotic Pets: Young children can get infected from exotic pets (lizards, snakes, birds).
• Species Details:
  • Two main species: Salmonella enterica and Salmonella bongori.
  • Part of Enterobacteriaceae family.
  • Salmonella enterica has six subspecies.

Serotypes and Pathogenicity

• Serotypes: 2,610 known serotypes.
• Common Serotypes:
  • Type E
  • Paratyphoid
  • Enteritidis
  • Typhimurium
• Antigens: Characterized by three surface antigens (flagellar H, O polysaccharide).
• LPS: Lipopolysaccharide O antigen.

Characteristics of Salmonella enterica

• Attributes:
  • Facultatively anaerobic, gram-negative, motile, non-sporing rod.

Clinical Manifestations

• Types of Manifestations:
  • Gastroenteritis
  • Enteric fever
  • Asymptomatic carrier state
• Asymptomatic Carriers:
  • Organism can colonize gallbladder.
  • Resistant to drug removal.
  • Small percentage of people remain carriers for life.

Epidemiology

• Most Affected Age Groups: Children under 5, elderly over 70.
• Symptoms: Food poisoning symptoms (diarrhea, cramps, headache, fever).
  • Duration: 5-7 days.
  • Incubation: As short as 6 hours.
• Seasonality: Peaks in summer and fall due to outdoor food handling practices.

Transmission and Hosts

• Primary Hosts: Domestic animals (cattle, poultry, wild birds).
• Prevalence in Animals: Nearly 100% in cattle, swine, and poultry.
• Infectious Dose: Varies by serotype; as low as 1,000 bacteria.
• Transmission:
  • Contaminated food, water.
  • Contact with infected feces or animals.
  • Zoonotic transmission possible.
  • Flies as indirect vectors.

Human Carriers and Shedding

• Shedding Duration: Up to 20 weeks post-recovery from non-typhoidal salmonellosis.
• Animal Carriers: Can excrete the organism intermittently or persistently.
• Non-Typhoidal Reservoirs: Domestic/wild animals, flies.

Treatment

• Antibiotic Sensitivity: Susceptible to chloramphenicol, ciprofloxacin, amoxicillin.
• Antibiotic Resistance: Some resistance noted to chloramphenicol.
• Treatment Necessity: Typically for severe cases requiring hospitalization.