Shigella

1. Shigella Belong to Enterobacteriaceae Gram negative bacilli Non motile, non capsulated NLF on MAC Deoxycholate citrate agar (DCA) selective media (pale color colonies) Dr B V Navaneeth, Dept of Microbiology

2. Shigella species Mannitol Non Fermentation Fermentation S dysentriae -12 S flexneri- 6 S boydii - 18 S sonnei (Late lactose fermenter) Dr B V Navaneeth, Dept of Microbiology

3. Epidemiology and Clinical Syndromes Major cause of bacillary dysentery Common in Pediatric age group (1-10 yrs) Estimated 15% of pediatric diarrhea in U.S. Leading cause of infant diarrhea& mortality in developing countries Developed world – S sonnei, developing world – S flexneri Outbreaks in daycare centers, nurseries, institutions Epidemics of S. dysenteriae type 1 have occurred in Africa and Central America with case fatality rates of 5-15%. Dr B V Navaneeth, Dept of Microbiology

4. Epidemiology and Clinical Syndromes Shigellosis = Generic term for disease Bacillary Dysentry Passing blood & mucus in the stool Low infectious dose (102-104 CFU) Humans are only reservoir Transmission by fecal-oral route Incubation period = 1-3 days Watery diarrheawith fever; changing to dysentery Dr B V Navaneeth, Dept of Microbiology

5. Infection cycle of Shigella Organisms adhere to colonic lymphoid follicles STOMACH Undergo parasite directed phagocytosis Resist intracelluar killing SMALL GUT Move directly from cell to cell Shiga toxin exacerbate inflammation by causing ishchemia & hemorrhage Ulcers LARGE GUT Rarely lead to bacteremia Dr B V Navaneeth, Dept of Microbiology

6. Pathogenesis Two-stage disease Early stage Watery diarrhea attributed to the enterotoxin activity ofShiga toxin inthe small intestine Second stage Dysenterydue toadherence and tissue invasion of large intestine(cytotoxic activity of Shiga toxin) Fever attributed toneurotoxic activity of toxin Shiga toxin Enterotoxic, neurotoxic and cytotoxic Similar to Shiga-like toxin of Enterohemorrhagic E. coli(EHEC) Dr B V Navaneeth, Dept of Microbiology

7. Virulence factors Invasiveness Attachment (adherence) and internalization with complex genetic control Large multi-gene virulence plasmid regulated by multiple chromosomal genes Exotoxin (Shiga toxin) Intracellular survival & multiplication Complications: Hemolytic uremic syndrome and reiters syndrome Dr B V Navaneeth, Dept of Microbiology

8. Clinical manifestation Fever Abdominal cramping & tenderness Diarrhea / Dysentry Tenesmus (straining at stools Sigmoidoscopy: ulceration Dr B V Navaneeth, Dept of Microbiology

9. Lab Diagnosis of Dysentry Specimens Stool, rectal swab from an ulcer (buffered glycerol saline- transport medium) Culture MAC NLF colonies DCA NLF TSI agar K-/ A - AST Report & Interpretations Dr B V Navaneeth, Dept of Microbiology

10. Shigella Dysentry- Differentiated from Dysentry like diseases Entero invasive E coli Campylobacter jejuni Entamoeba histolytica Balantidium coli Dr B V Navaneeth, Dept of Microbiology

11. Treatment For adults Rehydration if necessary Norfloxacin or ciprofloxacin Co-trimoxazole or ampicillin + rehydration For children Prevention No vaccines Human carriers identified & treated Water supply Sewage maintenance Breast feeding than formulas Dr B V Navaneeth, Dept of Microbiology

12. Summary Bacillary Dysentry Virulence factors Species of Shigella Clinical manifestation Source and spread Laboratory diagnosis Pathogenesis Antibiotics used Preventive measures Dr B V Navaneeth, Dept of Microbiology