gastrointestinal infections - bacteriology
DESCRIPTION
This is a series of lectures on microbiology, useful for both undergraduate and post graduate medical and paramedical students... This lecture covers cholera, typhoid, diarrhoea and dysentryTRANSCRIPT
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Gastrointestinal InfectionsDr. Ashish V. Jawarkar, MD (Path)
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• Most infections of the g.i.t. are acquired through contaminated food – food poisoning
• Food infection –− Bacteria like - Cholera, E. coli, Salmonella,
shigella, − viruses like enterovirus, rotavirus,
hepatitis A and E− Parasites like G. lamblia
• Food intoxication – S. aureus, B. cereus, Cl. Perfringens, Cl. botulinum
Overview
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Symptoms
• Abdominal pain
• Diarrhoea
• Vomitting
• Fever
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Factors responsible for spread
• Age – children more susceptible
• Personal hygiene
• Open air defecation
• Food at road side stalls
• Uncovered food
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Vibrio Cholerae
• Vibrio – vibrate – vibratory motility
• Present in surface waters worldwide
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• Morphology
• Growth characteristics
• Biochemical reactions
• Resistance
• Pathogenicity and virulence
• Epidemiology
• Diseases caused
• Laboratory diagnosis
• Treatment
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Morphology
• Short, curved comma shaped bacillus
• Single polar flagella
• Gram negative
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• Morphology
• Growth characteristics
• Biochemical reactions
• Resistance
• Pathogenicity and virulence
• Epidemiology
• Diseases caused
• Laboratory diagnosis
• Treatment
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Growth characteristics
• Aerobic
• Colorless colonies on mac conkey
• Special media− Transport media−Enrichment media− Plating media
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Transport media
• VR medium (Venkatraman, ramkrishnan)
• Cary blair medium
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Enrichment media
• Alkaline peptone water
• Monsur’s taurocholate tellurite peptone water
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Plating media
• TCBS medium – thiosulfate, citrate, bile salts and sucrose
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String test
• Loopful of colonies mixed with drop of sodium deoxycholate in saline
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• Morphology
• Growth characteristics
• Biochemical reactions
• Resistance
• Pathogenicity and virulence
• Epidemiology
• Diseases caused
• Laboratory diagnosis
• Treatment
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Biochemical reactions
• Cholera red reaction− Ferments glucose, mannitol, maltose,
mannose and sucrose− Produces indole which gives red color
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• Morphology
• Growth characteristics
• Biochemical reactions
• Resistance
• Pathogenicity and virulence
• Epidemiology
• Diseases caused
• Laboratory diagnosis
• Treatment
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Resistance
• Resistant to cold – refrigerated food may carry vibrio
• Donot survive at room temperature / heating
• Susceptible to common drugs like doxycycline
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• Morphology
• Growth characteristics
• Biochemical reactions
• Resistance
• Pathogenicity and virulence
• Epidemiology
• Diseases caused
• Laboratory diagnosis
• Treatment
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Cholera
• Acute diarrhoeal illness
• Painless ‘rice water’ stools
• Copius vomitting
• Fluid loss and dehydration
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• Due to two toxins released by bacteria in intestine
• Toxin A and B
• Cause pouring of water from body into intestines
• Extensive water depletion
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• Morphology
• Growth characteristics
• Biochemical reactions
• Resistance
• Pathogenicity and virulence
• Epidemiology
• Laboratory diagnosis
• Treatment
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Epidemiology
• Source – infected humans
• Mode of transmission – contaminated water/food
• Cholera spreads as sporadic/epidemic or pandemic forms
• Large movement of people such as during fairs/festivals is associated with cholera spread
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Sporadic
• Short duration infection limited to a small area
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Epidemic
• Suddenly many cases are seen over a large area
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Pandemic
• Cases seen over a long period of time over continents
• Till 19th century, cholera was mainly confined to India – mainly area of Ganga plains – Bengal
• Total seven pandemics have been identified.
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Seventh pandemic
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• Morphology
• Growth characteristics
• Biochemical reactions
• Resistance
• Pathogenicity and virulence
• Epidemiology
• Laboratory diagnosis
• Treatment
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Lab diagnosis
• Sample – stool – before administering antibiotics
• Use transport medium
• Dark field microscopy can be done for darting motility
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• Plated on TCBS medium
• Slide agglutination test
• String test
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• Morphology
• Growth characteristics
• Biochemical reactions
• Resistance
• Pathogenicity and virulence
• Epidemiology
• Laboratory diagnosis
• Treatment
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Treatment
• More important is replacement of lost fluid
• Antibiotics are of secondary importance
• Doxycycline
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Enterobacteria
• Flora of large intestine
• Classified on basis of growth on Mac Conkey’s medium− Lactose fermenters – E. coli, Klebsiella− Late lactose fermenters – shigella−Non lactose fermenters - Salmonella
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Diarrhoea causing E. ColiETEC
Entero toxicogenic
E Coli
Toxin causes release of water into intestinal lumen
Watery diarrhoea
EIEC
Entero invasive E Coli
Invade intestinal wall
Blood and mucous in stools
Dysentry
EHEC
Entero hemorrhagic
Does not invade
Toxin release
Bloody diarrhoea
Colitis
EPEC
Entero pathogenic
Infant watery diarrhoea
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Gram negative rods
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• E coli cause−UTI−Diarrhoea− Pyogenic infections−Septicemia
• Spread – feco oral route
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Salmonella – Enteric Fever - Typhoid
• Also causes gastroenteritis
• Motile gram negative rods
• Peritrichous flagella
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Salmonella – Enteric Fever - Typhoid
• Also causes gastroenteritis
• Motile gram negative rods
• Peritrichous flagella
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Growth characteristics
• Colorless colonies on Mac conkey – Non lactose fermenters
• Jet black colonies on Wilson and Blair due to production of H2S
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Growth characteristics
• Enrichment media−Selenite F broth− Tetrathionate broth
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Diseases caused
• Enteric fever
• Gastroenteritis
• Septicemia
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Enteric Fever (Typhoid)
• Pathogenesis
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Clinical course
• Gradual onset with fever, abdominal pain and constipation/diarrhoea
• Step ladder fever with bradycardia
• Spleen and liver are enarged
• Rose spots on skin in second week
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Complications
• Intestinal perforation
• Hemorrhage
• Shock
• Cholecystitis
• Osteomyelitis
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Epidemiology
• Source – food handlers/cooks−Carriers –
• Convalescent carriers – shed bacilli for 3 weeks to 3 months after cure
• Chronic carriers – more than 3 months after clinical cure
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Typhoid Mary
• New york cook – infected more than 200 persons – caused atleast 7 outbreaks
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Lab diagnosis
• Cases – Widal test, blood culture
• Carriers – isolation from bile
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Widal test
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Blood culture / Bile culture
• Take 45ml patient blood in bile broth
• Send to lab
• Cultured on Mac Conkey
• Lactose non fermenting colonies
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Treatment
• Chloramphenicol
• Ampicillin
• Co trimoxazole
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Prophylaxis
• Best is improved sanitation
• Live oral vaccine – typhoral
• Injectable vaccine – typhim vi
• Protection lasts 3 years, booster required afterwards
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Shigella – BACILLARY DYSENTRY
• DYSENTRY – bacillary (shigella) and amebic (parasitic)
• Also caused by EIEC, Campylobacter
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• Gram negative rods
• Lactose non fermenters on Mac conkey
• Classified according to mannitol fermentation−Sh dysenteriae – mannitol non
fermenter−Sh flexneri, sh bodydii and sh sonnei –
mannitol fermeters
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Bacillary dysentry
• Bacilli infect intestinal epithelial cells
• Spread to submucosa
• Inflammatory reaction with capillary thrombosis
• Sloughing and necrosis of mucosa
• Ulcers
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