Salmonella

Gastroenteritis, typhoid fever,paratyphoid fever

Salmonellae Over 2000 different antigenic types Originally classified into different species Now! Represent serotypes of a single species

Salmonella enterica Various subspecies Most mammals associated species are found

in subspecies enterica Example: S. enterica subspecies enterica

serotype Enteritidis Simply: S. Enteritidis

Serotypes Many are host-specific

Certain serotypes are major cause of food-borne infection

Most are benign and restricted

Some salmonellae cause life-threatening systemic infections (such as S. enterica serotypes Typhi and Paratyphi)

Description and antigenic structure

Enterobacteriaceae

Somatic or “O” antigen (heat-stable LPS)

Flagella or “H” antigen (heat-labile PP)

“H” antigen has two phases (1 and 2)

“Vi” (virulence) antigen in serotype Typhi

Kauffmann-White classification

Named salmonella as individual species

30 groups based on “O” antigen

Subdivided into groups by “H” antigen

Example: S. typhi (9,12, [Vi]:d-)

Host range and pathogenicity

Strains of S. enterica are widely distributed

Vertebrates GIT

Certain serotypes: flies and cockroaches

Asymptomatic to self-limiting gastro-enteritis

Morbidity, mortality and economical loss

Cholerae-suis (pigs)

Dublin (cattle)

Gallinarum-pullorum (poultry)

Abortus-equi (horses)

Abortus-ovis (sheep)

Other serotypes (no host preference)

Host adapted serotypes

Typhi, Paratyphi A, B and C

Primarily human pathogens

Only found in human

Occasionally, Paratyphi B isolated from cattle, pigs, poultry, exotic reptiles and other animals

Pathogenicity Enteric fever (typhoid and paratyphoid)

Typhi, Paratyphi A, B and C

Gastroenteritis and food poisoning Typhimurium

Bacteraemia Typhimurium Paratyphi C

Asymptomatic carriers

Enteric fever Caused by serotypes Typhi, Paratyphi A, B and C

These Salmonellae are usually found only in human

Execrated in faeces and urine of patients and carriers

Typhi is mainly water-borne Paratyphi is mainly food-borne

Penetration of ileal mucosa

Mesenteric lymph nodes

Lymph

Blood stream

Thoracic duct

Gall bladder Bone marrowLiver

Spleen

Primary bacteraemic phase (7-10 days of the incubation period)

Kidney

Second bacteraemia

Second bacteraemia

Fever and other sings

Fever and other sings

Intestine invasion inflammation and infiltration with mononuclear

followed by necrosis and ulceration

Other Salmonella infections Bacteraemia

Abscesses

Arthritis

Inflammation of gall bladder

Osteitis

Neonatal meningitis (S. typhimurium)

Laboratory diagnosis Enteric fever:

Blood , urine and stool

Diarrheal diseases Faeces and blood for culture

Bacteraemia Blood for culture

Abscesses and arthritis Pus for culture

Duration Rate of isolation Specimens

First 10 daysThird week

75-90%30%

Blood

Second weekThird week

40-50%80%

Faeces

After the second week

25% Urine

Specimen selection in enteric fever

Isolation

Aerobic incubation at 37 ° C

Faeces Selective media (XLD, DCA, MacConkey) Enrichment media (SF broth)

Blood culture

Morphology

Gram –ve motile rods

Non-sporing

Non-capsulated (except S. typhi)

Biochemical test for identification of bacteria

Serological diagnosis of enterica Antigen tests

Detect S. typhi in faeces Sensitive and specific Detect the bacteria in the first week

Antibody test When no culture or antigen test available Needs careful interpretation Has no value in case of food-poisoning

Shigella

Non-motile bacteria that conform with the definition of the family Enterobacteriaceae

Classification of Shigellae Based on antigenic structure and bioactivity

Group A: S. dysenteriae 12 different serotypes

Group B: S. flexneri 10 serotypes

Group C: S. boydii 18 serotypes

Group D: S. sonnei 1 serotype

Shigella infections Shigella cause bloody diarrhea

(dysentery) and non-bloody diarrhea. Often begins with watery diarrhea

accompanied by fever and abdominal cramps.

May progress to classical dysentery with scant stools containing blood, mucus and pus.

May be asymptomatic infection particularly in case of S. sonnei strains.

Rarely case other infections

Transmission

Infect only humans

Mostly person-to-person spread

Faecal-oral route through contaminated food and water

House flies

Only few organisms are required to cause infection

Epidemiology of Shigellosis The most virulent species is S. dysenteriae

serotype 1(Sd 1)

164.7 million case annually

163.2 in developing countries

1.1 million death

61% of mortalities in children < 5 years

Etiology

S. flexneri (60%)

S. sonnei (15%)

S. boydii (6%)

S. dysenteriae (6%)

In USA Annual reported cases = 20,000

Estimated undetected cases= 400,000

20% due to international travel

Common cause S. sonnei followed by S. flexneri

S. dysenteriae Shigellosis Inflammation and ulceration of intestine Severe dysentery (Shiga toxin) Dehydration and protein loss Abdominal cramps Rectal pain Toxaemia High fever High WBCs with neutrophilia

Causes of death

Circulatory collapse

Kidney failure

Bacterial virulence

Enterotoxin

Mainly due to bacterial invasiveness

Laboratory diagnosis Fresh faeces with enrichment media like Gram

Negative (GN) broth or Selenite broth.

Transport medium

pH alkaline

Culture in selective media XLD, DCA and MacConkey

Serological identification of Shigellae

Polyvalent O group antisera for groups A,B,C, and D

Monovalent O antiserum

e.g monovalent S. dysenteriae 1 for identification of Sd 1

The end