GIT micro

• Gastroenteritis


  Characterized by GIT symptoms like nausea, vomiting, diarrhoea and abdominal discomfort
• Diarrhoea


  Abnormal faecal discharge characterized by frequent and / or liquid stool, usually related to enterotoxin

  
• Dysentery


  Inflammatory disorder of the GIT with blood and pus in the faeces, pain, fever, abdominal cramps, usually related to invasive infection with mucosal destruction
• Damage resulting from GIT infection

  • Action of bacterial toxins, local or distant to site of infection
  • Local inflammation in response to superficial microbial invasion
  • Deep invasion to blood or lymphatics; dissemination to other body sites
  • Perforation of mucosal epithelium after infection, surgery or trauma
  • Gastric ulcers and cancer causing infections
• Bacterial pathogens of the GIT


  • Salmonella non-Typhi
  • Enteric fever (Typhi & Paratyphi)
  • E.coli
  • Shigella
  • Vibrio cholerae
  • Campylobacter
  • Clostridioides difficile
  • Bacteria causing food poisoning
  • Helicobacter pylori

  
• Viral pathogens of the GIT

  • Rotavirus
  • Norovirus
  • Hepatitis A and Hepatitis E
• Salmonella


  Typhoidal Salmonella cause typhoid & paratyphoid fever (Enteric fever), non-typhoidal Salmonella cause acute but self-limiting diarrhoea

  
• Salmonella


  • No animal reservoir for typhoidal Salmonella, large animal reservoirs for non-typhoidal Salmonella
  • Quite large infectious dose required: > 105 organisms

  
• Treatment of Salmonella


  1. Diarrhoea is usually self-limiting and resolves without treatment

  2. Fluid and electrolyte replacement

  3. Antibiotics use is discouraged as it does not reduce symptoms/shorten the illness and may prolong excretion of salmonellae in the faeces

  
• Enteric fevers: typhoid and paratyphoid


  Systemic infection initiated in the gastrointestinal tract, restricted to humans with no animal reservoir, spread from person to person, usually through contaminated food or water

  
• Enteric fever


  • Incubation period: 10–14 days (7–21 days)
  • Fever, malaise, aches, diarrhoea & constipation, rose spots are characteristic but absent in half of the patients

  
• Diagnosis of enteric fever


  Stool, blood culture, or culture from another body fluid/tissue

  
• Treatment of enteric fever

  Antibiotic treatment with ciprofloxacin or ceftriaxone, cefixime
• Prevention of enteric fever


  Public health measures, treating carriers, vaccination (injectable Typhim Vi or oral live-attenuated Ty21a)

  
• Types of E. coli

  • Enteropathogenic E. coli (EPEC)
  • Enterotoxigenic E. coli (ETEC)
  • Enterohaemorrhagic E. coli (EHEC)
  • Enteroinvasive E. coli (EIEC)
  • Enteroaggregative E. coli (EAEC)
• E. coli


  • Quite large infectious dose required: > 105 organisms

  
• Shigellosis (AKA bacillary dysentery)


  Caused by Shigella species which are human pathogens with no animal reservoir, spread from person to person by the faecal–oral route, primarily a paediatric disease

  
• Shigellosis


  • Symptoms range from mild to severe gastroenteritis, diarrhoea is usually watery at first, but later contains mucus and blood, with lower abdominal cramps
  • Invasion of the colonic mucosa causes inflammation & mucosal ulceration, S. dysenteriae produces shiga toxin which can damage the glomerular endothelial cells leading to kidney failure

  
• Campylobacter


  Curved or S-shaped Gram-negative rods, microaerophilic and thermophilic, large animal reservoir, acquired by consumption of contaminated food (poultry, milk or water), highly infectious with a dose as low as 500 organisms

  
• Campylobacter


  • Causes ulceration & inflamed bleeding mucosal surfaces in jejunum, ileum and colon due to invasion and cytotoxins, can lead to bacteraemia

  
• Cholera


  Caused by Vibrio cholerae, a comma-shaped Gram-negative bacterium that is a free-living inhabitant of fresh water, causes infection only in humans with no animal reservoir, can cause epidemics and pandemics

  
• Cholera


  • Classified into > 200 serogroups, only O1 and O139 serogroups cause epidemic cholera
  • Causes severe watery non-bloody diarrhoea known as rice water stool, leading to massive fluid loss & electrolyte imbalance, untreated mortality is 40-60%

  
• Cholera


  Caused by V. cholerae, a comma-shaped Gram-negative bacterium
• Cholera symptoms


  • Severe watery non-bloody diarrhoea is known as rice water stool
  • Massive fluid loss & electrolyte imbalance
  • Untreated- mortality is 40-60%
• Antibiotic-associated diarrhoea


  Caused by Clostridioides difficile, antibiotics disrupt normal gut flora and allows C. difficile to multiply

  
• C. difficile exotoxins


  Toxin A (enterotoxin) causes increased intestinal permeability & secretion of fluids, Toxin B (cytotoxin) -colonic inflammation, haemostasis and tissue necrosis in the colon

  
• Antibiotic-associated C. difficile diarrhoea

  • Diarrhoea, abdominal pain, fever after antibiotic treatment
• Staphylococcal Food Poisoning


  • Up to 50% Staph aureus produce enterotoxin, contaminated food, 50% people carry bacteria on skin & nose, heating kills bacteria but toxin is stable

  
• Staphylococcal enterotoxin


  Short incubation period: 1-6 hours after consuming contaminated food, presents with vomiting (diarrhea is not a feature), usually self limiting <24 hours
• Bacillus cereus


  • Spores survive cooking, germinate on cooling, present in soil, food

  Emetic form - rapid onset vomiting within 15min-4hrs due to the ingestion of enterotoxin in food (ingested preformed)

  Diarrhoeal form - watery diarrhoea within 8-12 hrs due to production of enterotoxin in the gut

  
• Botulism


  Toxins are ingested in food (often canned food), absorbed from the gut into bloodstream & reaches site of action i.e. peripheral nerve synapses

  
• Botulism


  • Characterized by a symmetrical descending flaccid muscle paralysis
• Clostridium gastroenteritis


  Anaerobic gram-positive spore forming rod produces enterotoxin, spore-contaminated food, inadequately cooked food

  
• Clostridium perfringens


  Abdominal pain & diarrhoea – usually self limiting, Necrotizing disease of small bowel, Enterotoxin

  
• Helicobacter pylori


  Gram-negative spiral bacterium, Infections are commonly asymptomatic, Symptoms-dyspepsia, upper abdominal pain, nausea, frequent burping, bloating, Associated with gastric & duodenal ulcers, acute & chronic gastritis, gastric adenocarcinoma, mucosa-associated lymphoid tissue (MALT) lymphoma

  
• Helicobacter pylori pathophysiology


  Urease breaks urea to ammonia and CO2, Increases pH and provides protection against gastric acid, Flagella
• Helicobacter pylori treatment


  Multiple treatments with Proton pump inhibitors and antibiotics
• Norovirus


  • Most common cause of diarrhoea worldwide (20% of all diarrhoea cases), > common in older children and adults, Highly infectious, spread rapidly, Nosocomial infection is common, Food- or water-borne routes, contaminated shellfish such as cockles or mussels, cruise ships outbreaks, aged care homes, barracks

  
• Norovirus diarrhoea


  Incubation period: 12–72 h, Nausea, abdominal pain, vomiting and diarrhoea, Recovery usually within 24–48 h
• Rotavirus


  • Infection is most common in children < 2 years of age, IgA antibodies in colostrum protects during the first 6 months of life, Outbreaks are sometimes seen in nurseries, Older children are less susceptible to infection