Salmonella (gastrointestinal)

D.A. Salmon in 1885,

Salmonella was named after

Salmonella (specifically identified as Salmonella cholerasuis)

first isolated as the causative agent of

hog cholera

Typical species of Salmonella that are commonly associated with diseases in various hosts.

• S. cholerasuis

• S. enteritidis

• S. gallinarum

• S. typhi

• S. typhimurium

S. salamae

Atypical Salmonellae

S. arizonae and related organisms

This group of Salmonella includes species that are less commonly encountered in clinical settings

S. houtinae and related organisms

Another lesser-known group within the genus of salmonella

S. bongori and related organisms

This group of salmonella is primarily found in reptiles and is less pathogenic to mammals.

Morphology of Salmonella

• are Gram-negative microorganisms characterized by their non-capsulated, short rod shape.

• They possess peritrichous flagella, which allow for motility, except for S. gallinarum and S.pullorum, which are non-flagellated.

Cultural characteristic of Salmonella

• can grow in aerobic and facultative anaerobic conditions, thriving on various media such as BGA, MacConkey agar, and bismuth sulfite agar.

Colonies of Salmonella

• typically measure 1-4mm in size and can be selectively grown using tetrathionate and sodium selenite.

• They can grow at temperatures ranging from 37°C to 43°C and produce gas from glucose,

  but do not ferment lactose.

Three main antigens of Salmonella

O, H, Vi

O antigen

• is determined by the polysaccharide structure of the cell wall

• designated by Arabic numbers (e.g., 1, 5, 7) and can change due to

  lysogeny, affecting serotype.

H antigen

• are heat-labile proteins.

• can exist in monophasic or diphasic forms, with only one form expressed at a time, a phenomenon known as the phase of Andrewes.

Phage typing of Salmonella

involves assessing the sensitivity of Salmonella cultures to a series of bacteriophages at specific dilutions, which helps in identifying and classifying serovars.

Transmission Salmonella

fecal-oral route, particularly in poultry where contaminated feed is a significant source of infection.

shedding the organism intermittently in feces or milk, contributing to the spread of infection.

how other animal become carrier of Salmonella

Phase 1: Colonization

(Pathogenesis of Salmonella Infections)

Salmonella colonizes the distal small intestine and colon, where indigenous bacteria inhibit its growth.

Phase 2: Invasion

(Pathogenesis of Salmonella Infections)

Salmonella penetrates the intestinal epithelium, multiplies, and can enter the bloodstream, leading to systemic infection.

Phase 3: Fluid Exsorption

(Pathogenesis of Salmonella Infections)

Inflammatory responses lead to increased secretion of fluids into the intestinal lumen, causing diarrhea and dehydration.

S. dublin and S. typhimurium

In cattle, _____ are the most significant pathogens

S. pullorum and S. gallinarum

In poultry, cause severe diseases such as bacillary white diarrhea and fowl typhoid, respectively.

S. pullorum

is particularly fatal to young chicks, with transmission occurring transovarially and through contaminated environments.

Symptoms of salmonellosis

diarrhea, septicemia, and in severe cases, can lead to death, especially in young or immunocompromised animals.

S. gallinarum

In poultry, can cause rapid anemia and leukocytosis, with significant mortality rates in affected flocks