Introduction to the Microbiology of the Gut Flashcards
Outline the mechanism of mucosal injury due to a viral infection
- Virus invasion
- Cell death, villous atrophy
- Crypt hyperplasia
- Enteroblast replacement
- Recovery
How does a GI viral infection cause diarrhoea?
Virus infection of enterocytes causes villus atrophy:
- Prevents absorption and increases secretion due to crypt hyperplasia causing watery diarrhoea
- Villus cells are continuosly replaced and villus architecture is restored within a few days and symptoms subside
Define food poisoning
Illness caused by the consumption of food or water contaminated with bacteria and/or their toxins, or with parasites, viruses, or chemicals’
Describe bacillus cerus
Toxin induced food posioning
- Endemic, soil-dwelling, Gram +, rod shaped bacteria, facultative aerobe
- Genus bacillus can produce protective endospores
- Emetic - Pre-formed toxin in food (0.5 - 6hr - peptide, heat soluble). Cooked rice common cause.
- Diarrhoeal - Bacterial spore germination, bacterial growth and toxin production in hut enterotxin (cytolytic - cerolysin). Pain and nausea
- Spores survive due to poor cooking. poor chilling allows spores to germinate. Bacterial growth produces enterotoxins
How is bacillus cereus diagnosed?
Emetic - Isolation of B.cereus from incriminated food
Diarrhoeal - Isolation from stools AND related food
How is bacillus cereus treated and prevented?
- Benign, self-limited illness, no treatment required
- Prevention:
- Bacteria grow best/survive b/w 4 to 60 degrees celcius
- Refrigerate food for storage
- Heat >60 degrees celcius before eating - Prevents germination of spores, bacterial growth or toxin production
Define microbiome
- Community of microorganisms that cna usually be found living together in any given habitat.
- ‘A characteristic microbial community occupying a reasonably well-defined habitat which has distinct physio-chemical properties.’ (Whipps et al,. 1988)
- Areas of human body with different microbiomes:
- Mouth
- Nose
- Skin
- Gut
- Genitals
- Hands
What are areas of the body without a microbiome?
- Brain
- Uterus
- Internal tissues
- Blood
- Subdermal
What are some of the microbes in the human microbiome?
- Bacteria
- Viruses
- Fungi
- Archaea
How are we able to detect the microbes in the microbiome?
- Microscopy
- Culture
- 16s rRNA gene sequencing
- Shotgun metagenomics
- Culturomics
Define symbiosis
Symbiosis is any type of a close and long-term biological interaction between two biological organisms of different species, termed symbionts, be it mutualistic, commensalistic, or parasitic
Define mutualism
A relationship between two species of organisms in which both benefit from the association
Define commensal
An organism that uses food supplied in the internal or the external environment of the host, without establishing a close association with the host, for instance by feeding on its tissues
Define parasitic
Parasitism is generally defined asa relationship between the two living species in which one organism is benefitted at the expense of the other.
Define pathogen
A bacterium, virus, or other microorganism that can cause disease/harm to host
What are the innate defences of the human gut, relates this to the gut microstructure
- Acid
- Fluids
- Bile
- Pancreatic fluids
-
Mucus:
- In the stomach, pit-mucus cells, gland-mucus cells, and chief cells are innate defences
- In the small intestine, there are goblet and paneth cells. Paneth cells secrete a number of antimicrobial peptides and proteins
- In the colon, there are goblet cells
- Peristalsis
- Epithelial shedding
- Immune cells
Describe dysbiosis
- An imbalance between the types of organism present in a person’s natural microflora, especially that of the gut, thought to contribute to range of conditions of ill health OR
- Change to the composition of resident commnesal communities relative to the community OR
- A disruption to the microbiome resulting in an imbalance in the microbiota, changes in their functional composition and metabolic activities or a shift in their local distribution
What are some microbiome therapies? Define them
- Probiotics - Live bacteria
- Prebiotics - Food that bacteria will like such as milk or fibre
- Postbiotics - Stuff that had bacteria in it but bacteria now either dead or filtered, intriguing
- Fermented foods - Such as yoghurt, salami, kimchi. Bacteria in these food are often lactobacilli and make lactic acid which stops other bacteria growing and so preserves the food
- Faecal microbiota transplants (FMT) - Blackbox therapy i.e. transfer whole of someone’s stool microbiome to another person
- Rewilding - Natural ways to replenish our microbiome and increase the number of microbes we come in contact with
Define gastroenteritis
An acute syndrome characterised by GI symptoms in any combination, including:
- Nausea
- Vomiting
- Diarrhoea
- Abdominal discomfort
Thought to be caused by an infection
What is diarrhoea? What are common viruses that cause diarrhoea?
- Watery/liquidy stools
- Usually with an increase in stool weight (i.e. volume)
- Above 200g per day
- An increase in daily stool frequency
- Often sense of urgency
Short term consequences can be excessive fluid loss, resulting in dehydration (hypovolemia) , electrolyte imbalance (hypokalaemia), disturbances in acid base balance.
Long term morbidity
Common viruses that cause diarrhoea:
- Rotavirus - Wheel like appearance
- Adenovirus - Looks bit like the hexagons in the bee movie in a black hole
- Calicivirus
- Norwalk - Ill-defined lacelike appearance
- Astrovirus
How can we determine if an infection is causing gastroenteritis?
Stool sample - Sent to microbiology/virology lab
- Diff viruses can be recognised by their characteristic morphology using electron microscopy
Alternatively, diagnostic techniques could be PCR, antigen detection e.g. EIA)
PCR IS COMMONEST METHOD USED NOW
Describe the pathogenic mechanism of vomiting induced by rotavirus and relate this to the symptomatology
Vomiting is characteristic of rotavirus infection
- Virus infects enterochromaffin cells
- (entero- and neuroendocrine cells)
- Stimulates production of 5’ hydroxytryptamine (serotonin)
- Activates vagal afferent nerves, which in turn activate cells of brain stem that control vomiting reflex (NTS)
Why can E.coli be pathogenic when it’s a mjor gut commonsal?
Can be further divided into strains, recognised by antigenic profile or other properties such as ability to cause disease or different biochemical properties
E.coli that live in GIT are commensals, don’t produce toxins or have any other disease producing mechanism
E.coli is GRAM NEGATIVE, has ROD LIKE APPEARANCE (BACILLI)
Describe the damage that enteropathogenic E.coli does to the intestinal tract
- Organism adheres closely to the mucosal cells of large bowel, disrupt brush border
- Verotoxin acts as a cytotoxin and enterotoxin in the gut
- Result in haemorrhage and oedema in the lamina propria with areas of superficial focal necrosis
