Gastrointestinal infections - bacteriology

Gastrointestinal InfectionsDr. Ashish V. Jawarkar, MD (Path)

• 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

Symptoms

• Abdominal pain

• Diarrhoea

• Vomitting

• Fever

Factors responsible for spread

• Age – children more susceptible

• Personal hygiene

• Open air defecation

• Food at road side stalls

• Uncovered food

Vibrio Cholerae

• Vibrio – vibrate – vibratory motility

• Present in surface waters worldwide

• Morphology

• Growth characteristics

• Biochemical reactions

• Resistance

• Pathogenicity and virulence

• Epidemiology

• Diseases caused

• Laboratory diagnosis

• Treatment

Morphology

• Short, curved comma shaped bacillus

• Single polar flagella

• Gram negative

• Morphology

• Growth characteristics

• Biochemical reactions

• Resistance

• Pathogenicity and virulence

• Epidemiology

• Diseases caused

• Laboratory diagnosis

• Treatment

Growth characteristics

• Aerobic

• Colorless colonies on mac conkey

• Special media− Transport media−Enrichment media− Plating media

Transport media

• VR medium (Venkatraman, ramkrishnan)

• Cary blair medium

Enrichment media

• Alkaline peptone water

• Monsur’s taurocholate tellurite peptone water

Plating media

• TCBS medium – thiosulfate, citrate, bile salts and sucrose

String test

• Loopful of colonies mixed with drop of sodium deoxycholate in saline

• Morphology

• Growth characteristics

• Biochemical reactions

• Resistance

• Pathogenicity and virulence

• Epidemiology

• Diseases caused

• Laboratory diagnosis

• Treatment

Biochemical reactions

• Cholera red reaction− Ferments glucose, mannitol, maltose,

mannose and sucrose− Produces indole which gives red color

• Morphology

• Growth characteristics

• Biochemical reactions

• Resistance

• Pathogenicity and virulence

• Epidemiology

• Diseases caused

• Laboratory diagnosis

• Treatment

Resistance

• Resistant to cold – refrigerated food may carry vibrio

• Donot survive at room temperature / heating

• Susceptible to common drugs like doxycycline

• Morphology

• Growth characteristics

• Biochemical reactions

• Resistance

• Pathogenicity and virulence

• Epidemiology

• Diseases caused

• Laboratory diagnosis

• Treatment

Cholera

• Acute diarrhoeal illness

• Painless ‘rice water’ stools

• Copius vomitting

• Fluid loss and dehydration

• Due to two toxins released by bacteria in intestine

• Toxin A and B

• Cause pouring of water from body into intestines

• Extensive water depletion

• Morphology

• Growth characteristics

• Biochemical reactions

• Resistance

• Pathogenicity and virulence

• Epidemiology

• Laboratory diagnosis

• Treatment

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

Sporadic

• Short duration infection limited to a small area

Epidemic

• Suddenly many cases are seen over a large area

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.

Seventh pandemic

• Morphology

• Growth characteristics

• Biochemical reactions

• Resistance

• Pathogenicity and virulence

• Epidemiology

• Laboratory diagnosis

• Treatment

Lab diagnosis

• Sample – stool – before administering antibiotics

• Use transport medium

• Dark field microscopy can be done for darting motility

• Plated on TCBS medium

• Slide agglutination test

• String test

• Morphology

• Growth characteristics

• Biochemical reactions

• Resistance

• Pathogenicity and virulence

• Epidemiology

• Laboratory diagnosis

• Treatment

Treatment

• More important is replacement of lost fluid

• Antibiotics are of secondary importance

• Doxycycline

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

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

Gram negative rods

• E coli cause−UTI−Diarrhoea− Pyogenic infections−Septicemia

• Spread – feco oral route

Salmonella – Enteric Fever - Typhoid

• Also causes gastroenteritis

• Motile gram negative rods

• Peritrichous flagella

Salmonella – Enteric Fever - Typhoid

• Also causes gastroenteritis

• Motile gram negative rods

• Peritrichous flagella

Growth characteristics

• Colorless colonies on Mac conkey – Non lactose fermenters

• Jet black colonies on Wilson and Blair due to production of H2S

Growth characteristics

• Enrichment media−Selenite F broth− Tetrathionate broth

Diseases caused

• Enteric fever

• Gastroenteritis

• Septicemia

Enteric Fever (Typhoid)

• Pathogenesis

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

Complications

• Intestinal perforation

• Hemorrhage

• Shock

• Cholecystitis

• Osteomyelitis

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

Typhoid Mary

• New york cook – infected more than 200 persons – caused atleast 7 outbreaks

Lab diagnosis

• Cases – Widal test, blood culture

• Carriers – isolation from bile

Widal test

Blood culture / Bile culture

• Take 45ml patient blood in bile broth

• Send to lab

• Cultured on Mac Conkey

• Lactose non fermenting colonies

Treatment

• Chloramphenicol

• Ampicillin

• Co trimoxazole

Prophylaxis

• Best is improved sanitation

• Live oral vaccine – typhoral

• Injectable vaccine – typhim vi

• Protection lasts 3 years, booster required afterwards

Shigella – BACILLARY DYSENTRY

• DYSENTRY – bacillary (shigella) and amebic (parasitic)

• Also caused by EIEC, Campylobacter

• 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

Bacillary dysentry

• Bacilli infect intestinal epithelial cells

• Spread to submucosa

• Inflammatory reaction with capillary thrombosis

• Sloughing and necrosis of mucosa

• Ulcers