Lecture 21. GI Infections 2

Morphology of Salmonella

Gram-negative, rod-shaped.

Salmonella

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Aerobic or Anaerobic nature of Salmonella

Facultative anaerobe and facultative intracellular.

Main species of Salmonella

1. Salmonella bongori

2. Salmonella enterica.

Important subspecies of Salmonella enterica in veterinary medicine

Enterica subspecies.

Types of Salmonella serotypes based on host adaptation

Host-restricted, host-adapted, and not host-adapted.

Examples of host-restricted Salmonella serotypes

1. S. gallinarum (chickens)

2. S. typhi (humans).

Examples of host-adapted Salmonella serotypes

1. S. Dublin (cattle)

2. S. abortusequi (horses/donkeys)

3. S. choleraesuis (pigs).

Examples of non-host-adapted Salmonella serotypes

1. S. typhimurium

2. S. enteritidis

3. S. saintpaul

4. S. newport.

Encounter of Salmonella in animals

Through fecal contamination; it is not part of the normal flora but can be transient.

Main route of entry for Salmonella

Fecal-oral route.

Multiplication and spread of Salmonella in the host

Intracellular replication → crosses epithelium → invades lamina propria → phagocytosed → spreads via lymphatics and circulation.

Survival of Salmonella inside the host

By surviving within macrophages (facultative intracellular).

Types of damage caused by Salmonella in the intestines

1. Malabsorption (hemorrhage)

2. exudation

3. hypersecretion,

Inflammation response to Salmonella leads to...

activation of adenylate cyclase, leading to fluid hypersecretion.

Key virulence factors of Salmonella

Flagella and fimbriae.

Factors contributing to susceptibility to Salmonella infection

Poor sanitation and immunocompromised hosts.

What are the three disease types associated with Salmonella

1. hemorrhagic enterocolitis (not enterotoxin)

2. septicemia

3. fetal infection

Clinical signs of hemorrhagic enterocolitis due to Salmonella

Foul-smelling, bloody diarrhea with mucus, vomiting, and fever.

Clinical signs associated with Salmonella septicemia

1. ischemia, terminal dry gangrene

2. endotoxemia

3. localized pneumonia, meningitis, arthritis.

Septicemia

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Effect of Salmonella on reproduction

Can cause abortion and luteolysis through PGF release.

Types of Salmonella carriers

1. Active (constant or intermittent shedding)

2. passive (fecal shedding without infection).

Diagnosis of Salmonella

1. History

2. clinical signs

3. cytology (neutrophils + RBCs),

4. culture.

Gold standard for Salmonella diagnosis

Bacterial isolation.

Samples needed for Salmonella isolation

10-15g feces (repeated 4-5 times), rectal biopsy, blood (for septicemia), or tissues from dead animals.

salmonella

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Diagnostic methods for acute Salmonella infections

Serology or PCR.

Detection of Salmonella carriers is done by

Repeated fecal culture, serology, or PCR.

Treatment for enteritis caused by Salmonella

Fluid therapy and antibiotics.

Treatment for endotoxemia with enteritis

Endoserum, polymyxin B, and NSAIDs.

Treatment for septicemia from Salmonella

Systemic antibiotics.

Key components of Salmonella prevention

Surveillance, sanitation, and vaccination.

Vaccination options for Salmonella

1. Repeated bacterins (serotype-specific)

2. autogenous bacterins

3. live attenuated vaccines (for cell-mediated immunity and potential cross-protection).

Importance of identifying and removing Salmonella carriers

Carriers are a persistent source of infection.