Salmonella & Shigella

Salmonella & Shigella

1. Salmonella

   • Gram negative ,motile ,facultative anaerobic bacilli
   • ➢ Non lactose fermenting colonies
   • Virulence factors
     • Fimbria - Endocytosis -Replication in microphage -Enterotoxin
   • Antigenic structure
     • O. Somatic antigen - H. Flagellar antigen - K. Capsular antigen
       • VI in Salmonella serotype typhi vs phagocytosis
   • Clinical Diseases
     • Acute gastroenteritis
       • Infective dose: 10^6 bacteria
       • Source :poultry, milk, egg
       • fever, chills, watery diarrhea and abdominal pain.
       • Self limiting.
       • In sickle cell ,hemolytic disorders , ulcerative colitis, elderly or very young patients; the infection may be very severe.
       • enterica the common cause
       • Management: Uncomplicated cases require fluid and electrolyte replacement only.
     • Typhoid fever
       • Prolonged fever
       • Caused by Salmonella serotype typhi or S. paratyphi
       • Dissemination to multiple organs
       • Common in (sewage ,poor sanitation).
       • Symptoms
         • First W:fever, malaise, anorexia, myalgia , dull frontal headache then constipation
           • Blood culture is positive.
           • 2nd and 3rd week: Sustained fever & prolonged bacteremia. ❖ Invade gallbladder and Payer's patches ❖ Rose spots
             • Organism isolated from stool
       • Managemant: - Ceftriaxone - Ciprofloxacin - Ampicillin -Azithromycin
       • Comlication : * Necrotizing cholecystitis - Bowel hemorrhage and perforation - Pneumonia

2. Shigella

   • non lactose fermenting Gram negative bacteria.
   • Cause bacillary dysentery
   • Antigenic structure
     • All have O antigens , some serotypes has K antigen( heat labile removed by boiling)
   • Low infective dose < 200 bacilli
   • ,leads to local inflammation, shedding of intestinal lining and ulcer formation.
   • Symptoms : High fever, tenesmus , bloody stool with mucus & leukocytes.
   • Complications: ileus, obstruction dilatation and toxic mega colon
   • Treatment : similar to salmonella But Azithromycin not used