INF1 - E. GI INFECTIONS-COVERED Flashcards
where can bacteria enter the body
- resp tract
- GI tract (includes mouth!)
- urogenital tract
- breaks in skin surface
what causes food borne illnesses
- viruses (norovirus, hepatitis A) - most common cause of gastro-enteritis
- bacteria (salmonella, campylobacter)
- parasites (tapeworms in contaminated food)
- prions (BSE in cattle and therefore in contaminated meat)
- chemicals
how to GI pathogens infect us
- microbes live in GIT
- released in faeces of animals/humans
- ingested of organisms and toxins by humans by food, fluids, fingers
- organisms multiply and toxins produced, infection remains localised in GIT = diarrhoea/vomiting
or - organsims invade/ toxins absorbed and infection spreads = systemic infection symptoms
- pathogen excreted in faeces
how does bacteria attach to host cells
Loose association of bacteria to mucous layer then attachment and entry of bacteria into epithelial cell, bacteria can then enter bloodstream
- direct protein-protein interaction
- indirect interaction with slime layer or capsule
- fimbriae and pili on surface of bacteria
what are exotoxins
- secreted extracellularly by gram-ve and gram+ve cells
- proteins and heat labile
- ie: cytolytic toxins, A-B toxins, superantigen toxins
- if systemic: highly toxic, antigenic, fever, adhesion to specific host cell receptors
what are enterotoxins (entero/enteric = intestine)
- form of exotoxin
- secretion of fluid into lumen of small intestine
- proteins and heat stable
- produced by enteric pathogens: V. cholera, E. coli
what are endotoxins
- LPS present on cell wall of gram-ve bacteria (cell lysis)
- breakdown of LPS gives rise to lipid A, core polysaccharide, O-polysaccharide
- fever and diarrhoea, reduced white blood count, release of cytokines, infammation
what is the microbiome
ecological community of commensal, symbiotic and pathogenic microorganisms found in and on all multicellular organisms
what is microbiota
specific micro-organism living at a specific site ie - gut microbiota
what does the microbiome do
- involved in maturation and development of our immune system
- involved in metabolism of some nutrients that we can’t perform ourselves
- competition and habitat filtering: colonisation resistance
- conversion of fibre into fermentation products: nutrition
- detection of metabolites by host cell receptors: immune education
- if balance is disrupted = colonisation/over-population of certain microbes, infection and disease
what does the GIT microflora consist of
- 10^14 bacteria
- majority in lower GIT (anaerobic compared to upper GIT which is aerobic)
- bacteria, archaea, fungi, bacteriophages
- one of the most dense and complex microbial ecosystems
what is the role of the GI microbiota
- digest materials by producing enzymes the host doesn’t and provide important materials
- indigestable plant sugars converted into short chain fatty acids
- biotin (vitamin B7) - coenzyme for carboxylase enzymes
- panthotenic acid (vitamin B5) - essential for production of nucleotides
- folic acid (vitamin B9) - essential for production of nucleotides
- precursor to vitamin K - required for blood clotting - compete with pathogenic microorganisms
- reduces risk of colonisation by pathogenic microorganism via competition
- removes nutrients
- changes extracellular pH - influences immune system
- improves response to pathogenic bacteria
- modulates the function of the T-cells in gut epithelium
what are probiotics
- microorganisms that live in gut (bacteria and yeast)
- probiotic foods contain beneficial organisms that help colonise and populate gut
- foods: yoghurt, tempeh (any fermented food)
what are prebiotics
- indigestible food ingredients that act as a food source for probiotics
- foods: leeks, garlic, onion, legumes
what infections can you get in the GIT
- mouth: periodontal disease
- stomach: gastric ulcer disease and gastroenteritis
- intestines: gastroenteritis, diarrhoea, dysentery, enterocolitis (C.diff)
what is gastroenteritis
inflammation of the GI mucosa that involves stomach and small intestine
symptoms of gastroenteritis
diarrhoea
vomiting
abdominal pain and cramps
what causes gastroenteritis
virus (most common) or bacteria infection
how is gastroenteritis contracted
eating contaminated food or person-to-person contact
treatment of gastroenteritis
often self-limiting
more severe bacterial infections - antibiotics
why should you not wash raw chicken
- Campylobacter lives on chicken and is killed by heat (ie - oven)
- Campylobacter in water droplets can splash onto work surfaces, clothes, skin
what bacteria genus is the most common cause of gastroenteritis and diarrhoeal disease
campylobacter (gram -ve,curved rods, motile)
how is campylobacter transmitted
contaminated food (poultry, shellfish) or faecal-contaminated water
(campylobacter lives in intestinal tract of food-chain animals like poultry and cattle)
what happens after ingestion of campylobacter
- multiplies in small intestine
- adheres to epithelium
- invades epithelial cells
- causes inflammation, releasing toxins, symptoms
