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

The antigenic formula O Phase 1 H Phase 2 H : : Paratyphi B 1,4,5,12:b:1,2

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 marrow Liver Spleen Primary bacteraemic phase (7-10 days of the incubation period) Kidney Second bacteraemia Fever and other sings Intestine invasion inflammation and infiltration with mononuclear followed by necrosis and ulceration 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

DurationRate of isolationSpecimens First 10 days Third week 75-90% 30% Blood Second week Third 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)  million case annually  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

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