SHIGELLA
Foodborne Diseases
• Worldwide Diarrheal diseases are second only to Respiratory diseases as a
cause of adult death
• Leading cause of child death in Asia, Africa and South America
• Each year 5 million children (13,600/day) die due to Diarrheal diseases
SHIGELLA MORPHOLOGY
• Gram negative bacilli
• Non-motile
• Nonspore-forming
• Capsulated
• Genetically closely related to E. Coli
• Named after kiyoshi shiga, who first discovered it in 1897
Common species
• 1. Shigella dysenteriae: serious form of bacillary dysentery
• 2. Shigella flexneri
• 3. Shigella sonnei
• 4. Shigella boydii
All four species cause dysentery, Abdominal pain, Bloody stool, and Diarrhea
Shigella
• Causative agent of shigellosis or bacillary dysentery
• Involved in foodborne outbreaks
• According to the Center for Disease Control and Prevention Shigella is the
third most reported foodborne bacterial pathogen
• Spread is always from a human resource
CULTURAL CHARACTERISTICS
• Aerobic and facultative anaerobes
• pH: 6.4 to7.8
• Mesophiles
• Temperature: 10- 45◦C (Opt temp 370)
• Size: 1-3 um X 0.5 um
• Colony diameter: 1- 2 mm
, • Colonies: circular, convex, colourless, moderately translucent with smooth
surface
• Non-lactose fermenting
• Bile salts resistant:
• Ferments glucose
• Reduce nitrates (NO3 to NO2 or N2)
• Oxidase: negative
Selective Medium
• In XLD (Xylose lysine deoxycholate ): pinkish to reddish colonies
• Heaktoen Enteric Agar (HEA): green to blue green colonies
• Mac Conkey agar
• Salmonella Shigella (SS) agar
• EMB
Factors Contributing Spread
• Spread is always from a human source and generally involves one of the five
f`s
• `` Food, fingers, flies, feces and fomites``
• Reservoir: Strict human pathogen
• Human colon, food, feces, but doesn't live long outside of host
• Infectious dose: 10 -100 viable organisms
• Incubation period: 1-4 days
PATHOGENESIS
• Oral >>> Stomach >>> Small Intestine >>>large intestine >>>Feces>>>Oral
Infection Process
• Ingestion
• First stage: Non-invasive colonization of intestinal epithelial cells
• Reproduction within 12 hours in small bowel
• Production of enterotoxin in the small intestine
• Second stage: In 1 to 4 days moves to large intestine
• Adherence and tissue invasion of large intestine
• Ulceration
• Typical symptoms of dysentery
• Non systemic
• Self- limiting, lasts a few days to a month
• Cytotoxic activity of Shiga toxin increases severity
Foodborne Diseases
• Worldwide Diarrheal diseases are second only to Respiratory diseases as a
cause of adult death
• Leading cause of child death in Asia, Africa and South America
• Each year 5 million children (13,600/day) die due to Diarrheal diseases
SHIGELLA MORPHOLOGY
• Gram negative bacilli
• Non-motile
• Nonspore-forming
• Capsulated
• Genetically closely related to E. Coli
• Named after kiyoshi shiga, who first discovered it in 1897
Common species
• 1. Shigella dysenteriae: serious form of bacillary dysentery
• 2. Shigella flexneri
• 3. Shigella sonnei
• 4. Shigella boydii
All four species cause dysentery, Abdominal pain, Bloody stool, and Diarrhea
Shigella
• Causative agent of shigellosis or bacillary dysentery
• Involved in foodborne outbreaks
• According to the Center for Disease Control and Prevention Shigella is the
third most reported foodborne bacterial pathogen
• Spread is always from a human resource
CULTURAL CHARACTERISTICS
• Aerobic and facultative anaerobes
• pH: 6.4 to7.8
• Mesophiles
• Temperature: 10- 45◦C (Opt temp 370)
• Size: 1-3 um X 0.5 um
• Colony diameter: 1- 2 mm
, • Colonies: circular, convex, colourless, moderately translucent with smooth
surface
• Non-lactose fermenting
• Bile salts resistant:
• Ferments glucose
• Reduce nitrates (NO3 to NO2 or N2)
• Oxidase: negative
Selective Medium
• In XLD (Xylose lysine deoxycholate ): pinkish to reddish colonies
• Heaktoen Enteric Agar (HEA): green to blue green colonies
• Mac Conkey agar
• Salmonella Shigella (SS) agar
• EMB
Factors Contributing Spread
• Spread is always from a human source and generally involves one of the five
f`s
• `` Food, fingers, flies, feces and fomites``
• Reservoir: Strict human pathogen
• Human colon, food, feces, but doesn't live long outside of host
• Infectious dose: 10 -100 viable organisms
• Incubation period: 1-4 days
PATHOGENESIS
• Oral >>> Stomach >>> Small Intestine >>>large intestine >>>Feces>>>Oral
Infection Process
• Ingestion
• First stage: Non-invasive colonization of intestinal epithelial cells
• Reproduction within 12 hours in small bowel
• Production of enterotoxin in the small intestine
• Second stage: In 1 to 4 days moves to large intestine
• Adherence and tissue invasion of large intestine
• Ulceration
• Typical symptoms of dysentery
• Non systemic
• Self- limiting, lasts a few days to a month
• Cytotoxic activity of Shiga toxin increases severity
