Digestive Microbiology

Question 1

What are the types of food-borne contamination, identify the types of diagnostic services and which bacteria is used.

Answer 1

• Microbial; this looks into the actually count og micrbes present on contaminated consumables, and if enough present could cause infection
• Spores; might be build up of vegetative cells in products that ill bne consider at a later date(e.g. rice)
• Toxin; prodution of tozin that could be heat-liable or stable, liable means that cookign the poruct will reduce change of infection wilst stable means heaty impreoable.

*Note the GBRU has several method of detecting microbes or infection-causing organisms; culture being the typical gold standard for identification. Serotyping; looks at the antigen available on the surface of the outer membrane to be abe to identify it (e.g. salmonella spices). PCR(as you know it). MLST (e.g. campylobar)

Question 2

Outline the 2 types of bacterial diarrhoeas and give examples.

Answer 2

1. Enterotoxin-mediated; Enterotoxins have a particularly marked effect upon the gastrointestinal tract, causing traveler’s diarrhea and food poisoning. The action of enterotoxins leads to increased chloride ion permeability of the apical membrane of intestinal mucosal cells. Summary: Fluid loss via watery stool, and bacteria colonizes upper small intestine. (e.g. Enterotoxic e. coli, shiglla, vibrio, s. aureus)
2. Invasive; asthe response.of the human gastrointestinal tract to enteric pathogens- such as bacteria (Shigella, Salmonella, Campylobacter, and enteroinvasive Escherichia coli), viruses (rotavirus). Destroys epithelial cells + watery stools.

Question 3

Outline the 3 types of toxins and give examples for each.

Answer 3

• Neurotoxins; occurs when the exposure to natural or manmade toxic substances (neurotoxicants) alters the normal activity of the nervous system. This can eventually disrupt or even kill neurons. This can occur directly(toxin is attacking neurons directly) or indirectly(via altering intracellaurl meidtaori which will then alter normal cell behabior). (e.g. s. aureus)
• Cytotoxins; toxins that is general toxic to any/various cells inducing apoptosis or necrosis. (e.g. C. difficile, shigella)
• Enterotoxins; frequently cytotoxic and kill cells by altering the apical membrane permeability of the mucosal (epithelial) cells of the intestinal wall. This can occur directly or indirectly(via altering intracellaurl meidtaori which will then alter normal cell behabior). (e.g. vibrio cholera)

Question 4

What is the cascade of E. Coli enterotoxins? (DRAW)

Question 5

Define/differentiate between selective and differential media. Give examples of agar mediums, the bacteria grown on them, and appearance on positive results.

Answer 5

Selective; Selective media areused to select for the growth of a particular “selected” microorganism. For example, if a certain microbe is resistant to aparticular antibiotic (e.g., novobiocin), then that antibiotic can be added to the medium in order to prevent other organisms, which are not resistant, from growing. (e.g. mannitol salt agar, s. aureus is grown appearnce is seen in image)

Differential; contain compounds that allow groups of microorganisms to be visually distinguished by the appearance of the colony or the surrounding media, usually on the basis of some biochemical difference between the two groups. (e.g. blood agar - grows s. pneumoinia appearnnce is a greenish halo on blood agar plates referred to as alpha-hemolysis, mcconkeys)

• Selective media generally selects for the growth of a desired organism, stopping the growth of or altogether killing non-desired organisms. Differential media takes advantage of biochemical properties of target organisms, often leading to a visible change when growth of target organisms are present.

Question 6

Outline Campylobacter’s parameters of life/what it is and what disease it causes and at what dosage.

Answer 6

Campylobacter is a genus of Gram-negative bacteria. Campylobacter typically appear comma- or s-shaped, and are motile. They’re microaerophilic and unable to ferment carbs. Identification can be via culture, gram stain, and oxidative test. (doesn’t growth in <28C).

Gastroenteritis isa very common condition that causes diarrhoea and vomiting. It’s usually caused by a bacterial or viral tummy bug. 50% of cases have no known aetiology.

Question 7

Where is Campylobacter predominately found?

Answer 7

Campylobacter is predominately found in poultry(on skin and even packaging). Can also be found in beef and pork products or may be contracted from animal contact. mainly from food but some cases have no known origin. The infection does of Campylobacter is as low as 360CFU.

Question 8

Outline shigella’s survival parameters/what it is and how its identified.

Answer 8

Shigella is a genus of bacteria that is Gram-negative, facultative anaerobic, non-spore-forming, nonmotile, rod-shaped, and genetically closely related to E. coli. The genus is named after Kiyoshi Shiga, who first discovered it in 1897….NOTES

Question 9

What disease does shigella cause? Explain the multifaceted disease, lifecycle, and Pathogenesis.

Answer 9

There are four species of shigella all of which vary in disease severity(S. dysenteriae is most severe, S. boydii is least). Shigella has a fecal/oral infection route as a result of poor sanitation/hygiene and it has a low infectious dose(10-100 cells). Infection features mucus and blood in watery diarrhea.

Furthermore, shigella is multifaceted disease(2 stages):

1. Early; watery diarrhea and enterotoxin activity in small intestine
2. Second; dysentery, adherence and tissue invasion of large intestine, cytotoxic activity of shiga toxin.

**Shiga toxin; enterotoxin and cytotoxic as it inhibits protein synthesis by lysing 28SrRNA.*

DRAW LIFE CYCLE.

• Entry to host; orlay - stomach - gut
• invasion; type 3 secretion system (T3SS) , also called the injectisome, is one of the bacterial secretion systems used by bacteria to secrete their effector proteins into the host’s cells to promote virulence and colonisation. The T3SS is a needle-like protein complex found in several species of pathogenic gram-negative bacteria.like machinery

Question 10

Brief notes on listeriosis and salmonella.

Answer 10

Listeriosis

Listeria monocytogenes is the species of pathogenic bacteria that causes the infection listeriosis. It is a facultative anaerobic bacterium, capable of surviving in the presence or absence of oxygen and can grow in 0-42C. Healthy individuals that may get infected from contaminated consumables(fish, cheese, milk) will usually recover as this is self-limiting, but may experience febrile gasterioeteritis. Those who are at risk when it comes to infection include: pregnant women, elderly, immunocomporsed.

Symptoms; nausea, airhead, abdominal pain, fever.

Salmonella

Salmonella is a genus of rod-shaped Gram-negative bacteria of the family Enterobacteriaceae. The two known species of Salmonella are Salmonella enterica and Salmonella bongori. Its a facultative anaerobe and growth in at body temp.

INFECTION PROCESS…