Lecture 13- Lec 12 Part 2

Question 1

Lower GIT

Answer 1

Comprises of small + large intestine; segment of the GI tract from the jejunum (just after the duodenum- start of small intestine) to the anus

Upper GI- involved in transport, protection, mechanical + enzymatic digestion

Lower GI; digestion, absorption, defecation + protection; slide 4

Question 2

Microbiome

Answer 2

99% of gut= anaerobic

Anaerobic bacteria= use fermentation to break down indigestible fibres + produce nutrients

Question 3

Recovery of host microbiome post stomach acid

Answer 3

Exposure to bile, stomach acid is neutralised

1.pH through the GIT becomes more hospitable
2.O2 levels drop as the GI tract progresses
3.Bacterial cell numbers start to recover

Question 4

Mucus membranes + microbiota

Answer 4

Discrete bacterial communities can develop in niche microhabitats; gut lumen, colon mucosal layers + colon crypts

Bacterial community dependent on= oxygen conc, pH, antimicrobial peptides + nutrient sources available

Question 5

Factors affecting gut microbiome composition

Answer 5

Gut microbiome constantly adapts due to genetic + external/environmental pressures

Age= factor in early years (most gram +), later life becomes gram - rods

Usually= baseline state, can change in response to= illness, meds, emotional stress, diet etc

Question 6

Competition by commensal microbes

Answer 6

Slide 9

Offers protection;
-can restrict colonisation by pathogens through competitive exclusion
-some members also produce antimicrobial agents that inhibit growth of pathogens

Question 7

Mucus + production of antimicrobial agents

Answer 7

Gut mucosal epithelial cells= secrete a wide range of antimicrobial agents

Gut= paneth cells- found in intestinal crypts produce granules which contain

-lysozyme= breaks down PDG
-phospholipase= phospholipase by layer in membranes
-lectins= bind to carbs, pore forming in bacteria
-defensins= small antimicrobial peptides, defend stem cells which replicate to form new villi

Question 8

Gut Associated Lymphoid Tissue (GALT)

Answer 8

Gut mucosa= hosts the body’s largest population of immune cells
Dendritic cells in GALT= sample the intestinal contents for pathogens
DC= use dendrites to pass through the M cell + sample bacteria/antigens for PAMPs

Method; slide 11

Question 9

Exclusion zone for host to maintain control

Answer 9

Work in conjunction with mucus to provide a bacterial “exclusion zone”. Physical separation of the small intestine surfaces + the gut microbiome

Exclusion zone not present?
- higher rates of infection + cancers due to constant inflammation
- no appropriate control

Question 10

Bacterial killing by antimicrobial peptides

Answer 10

Defensins; host defence peptides (20-50 AA in size)
- kill bacteria entering crypts to protect stem cells + epithelium and avoid infection

Question 11

Campylobacter jejuni

Answer 11

Opportunistic foodborne pathogen
Spiral spirochete shaped; may become coccoid under stress
Gram -
Facultative intracellular pathogen
Colonises the intestinal mucosa

Question 12

Transmission- C. Jejuni

Answer 12

Zoonotic infection- transmitted to humans by animals

Main route of C.jejuni transmission raw/undercooked poultry

Other routes; pork, beef, contaminated water

Chickens intestinal microbiome; produces little-no clinical observations in poultry

Post slaughter;
Cross-contamination in the kitchen can be a problem
Direct (faecal-oral route) / indirect transmission

Question 13

Mechanism of infection- C. Jejuni

Answer 13

Mechanism of infection- not understood. Surface of C.jejuni helps to evade host defences

Evasion of host defences;

1. Lipooligosaccharide (LOS)= glycolipid vital for integrity of the outer membrane + resistance to bile salts. Can display molecular mimicry of host structures
2. Capsule; a polysaccharide coat that may mask underlying antigens + confer resistance to phagocytosis + other innate defences
3. Protein glycosylation; adds carbs moiety to a protein
   - may mask bacterial antigen. Hides them from immune cells

Question 14

Mechanism of infection- C.jejuni

Answer 14

Flagella; role in motility, adhesion & protein injection into host cells

Adhesions; outer membrane proteins- mediate attachment to epithelial cells

Protein secretion systems- flagella mediated- cell cytoskeleton rearrangement

Iron acquisition systems

Production of cytolethal distending toxin

Question 15

Cytholethal distending toxin (CDT) damages the human intestine

Answer 15

CDT holotoxin- 3x subunits, CdtA, CdtB + CdtC; CdtB= effector

CdtA+ CdtC= bind a host cell receptor mediating entry via clathrin-coated pits= formation of vesicle

CdtB -> transits to the nucleus = causes double-strand DNA breaks + cell cycle arrest= human cell death

Question 16

Infection in humans; Campylobacteriosis

Answer 16

Incubation period; 2-5 days after ingestion
-small + large intestines colonised
Inflammatory diarrhoea, haemorrhagic
Fever, nausea, abdominal cramps + pain= symptoms
Self limiting + symps last 5-7 days
Intestinal ulceration + perforation observed sometimes

Question 17

Enrichment + detection of campylobacteriosis + treatment

Answer 17

Relies on collection of a faecal sample
Enrichment media may contain;

-ferrous sulphate, sodium metabisulphate + sodium pyruvate= quench toxic compounds + increase aero tolerance

-lysed horse blood= quench oxygen + provide a source of iron

Antibiotics; vancomycin, cefoperazone + trimethoprim

Identification; API, DNA sequencing

Treatment;
-self limiting
-antibiotics= erythromycin- (a macrolide)- shortens the duration of symptoms if given early
-quinolone antibiotics; ciprofloxacin/levofloxacin= no longer as effective owing to resistance
-dehydrated patients= IV + electrolyte therapy

Question 18

Salmonella

Answer 18

Typhoidal; causes typhoid fever
Non-typhoidal; self-limiting gastroenteritis in immunocompetent individuals- food poisoning

Difference= NT salmonella doesn’t cause sepsis like TS because NTS infections are usually confined to the intestines whereas TS infections spread throughout the body
Slides 29-37

Question 19

Clostridioides difficile

Answer 19

Slides 37-44

Question 20

Fungal infections of the lower GI tract

Answer 20

Fungi makes up 1-2% of the intestinal microbiome- essential for digestion + protection

Reasons for fungal GI infections; immunocompromised host, antibiotic use, diet= overgrowth of fungi in the gut

Blood stream infection can result in; sepsis, septic shock + death

Question 21

Obesity with bacteria

Answer 21

Gut microbiome from lean humans can offer protection against body fat gain in experimental mice

Slide 46

Question 22

Listeria monocytogenes

Answer 22

Gram +
Facultative anaerobe
Psychrophile
Can cross the placental, intestinal + blood-brain barrier

Transmission;
Found in soil, water + animal digestive tracts
Bacteria can contaminate food during harvesting, processing, prep, packing, transportation or storage

Common routes;
Eating contaminated foods, mother-child transmission, pets etc

Question 23

Infection in humans- listeriosis

Answer 23

Incubation period of 7-70 days after ingestion
Mild fever+ diarrhoea in immunocompetent pts
Self limiting + symptoms rarely diagnosed- can last days-weeks
Extra intestinal invasion in preg women

Question 24

Complications of listeriosis

Answer 24

1- extra-intestinal spread can occur in immunocompromised-deficient patients= sepsis, meningitis, convulsions, muscle ache, loss of balance + fever

2- can migrate across the placenta- loss of the unborn foetus, pre-term labour, infection of newborn etc

Treatment=
-self limiting
Antibiotics= ampicillin, gentamicin= administered early for those with complications
Dehydrated pts= IV + electrolyte therapy
Monitor unborn child