Chapter 4 - B

Question 1

Locations of the microbiota include

Answer 1

Any parts of the body that is exposed to the environment are not sterile

Stomach is not sterile

most of our microbiota is located in the surface epithelial tissues which are normally exposed to environment

Question 2

Skin:

Answer 2

Composed of a tightly packed continuous layer of cells impregnated with the protein keratin

Constantly undergoing renewal with production of new skin cells and the sloughing of dead ones (desquamation)

• new skin on the bottom, dead skin on top
• makes it harder to infect skin on top layer

Question 3

Skin

Secretions:

Answer 3

sweat

Sebum: oily waxy substances produced by sebaceous glands

• coats moisturize and protect skin
• Also contains lysozyme to break down pathogens

no mucous

Question 4

Skin Microbiota:

Answer 4

The average adult has 2m^2 of skin

On human population basis, 100s of bacteria species identified by culture dependant and independent methods

Environmental conditions vary depending on the skin site, dictates what grows there
- Thus microbiota varies with the skin site

Question 5

We have more bacteria post-wash

Answer 5

Dead layer of skin is washed off and its the bacteria on the living skin surface that is picked up

Question 6

Skin

Answer 6

Dry areas - less organism per area

Moist area - more organism per area

Question 7

Skin environments that impact microbiota

Answer 7

Most areas that evaporate of sweat is hindered

• Most of the skin is mildly acidic dry and salty
• Hair follicles are mostly located in moist area
• Sweat, sebum are mildly acidic
• Sweat and sebum contains salts, evaporation and water increases salt concentration
• Sebum contains lipids, aa, urea, lactic acid: used as nutrients by microbiota

Question 8

Examples of Skin Microbiota:Propionibacterium acnes

Answer 8

Aerotolerant anaerobe

• Lives at the base of hair follicles
• Ferments components of sebum producing propanoic acid
• Lowers pH of skin further
• Overproduction of sebum can lead to acne because of the large amount of fermentation products that lead skin to inflame

Question 9

Examples of Skin Microbiota: Staphylococcus aureus

Answer 9

Pathogen that can exist harmlessly as part of the skin and nasal microbiota in some people

If it gains access to body through bacteria in skin or nasal epithelium it can make use of many aggressive virulence factors that can contribute to serious disease

Question 10

Examples of Skin Microbiota: Staphylococcus epidermidis

Answer 10

Found as a major component of skin microbiota of all people

Doesn’t seem to have any aggressive virulence faclts like S . aureus

But it is the most important causes of infection associated with catheterization including peripheral and central intravenous catheters
- Nosocomial infection

Because it is found in the skin when the catheter is put in the skin, high probability that bacteria will get into the blood

Despite lack of aggressive virulent factors, immune system have difficulties clearing long lasting S. epidermidis infections despite production of antibodies against it
- May be a reflection of that fact that immune system has evolved not to react in a strong manner to prevalent commensal bacteria of microbiota

Question 11

Microbiota of the oral cavity

Answer 11

Gingival crevices anaerobic bacteria

tooth surfaces aerobic

On human population baes, hundreds of different species identifies by culture dependent and independent method

Question 12

Microbiota of the oral cavity

Answer 12

Although the oral microbiota are diverse, they are not a very abundant
- only a few billion

THis is because saliva has pH of around 7

• mostly water, mucus and digestive enzymes
• not much nutrients for bacteria unless just eaten meals
• brush/floss

Salivary flushing and epithelial shedding removes bacteria and send ti to stomach and gets kill by acid

Maintaining a presence in the oral cavity depends on being able to attach to surfaces and form a biofilm

Biofilms on teeth are the most studied

tooth biolfilm is not plaque

Question 13

Streptococcus mutans

Answer 13

Is a member of oral microbiota

Aerotolerant anaerobe
: likes to be gin gingival crevices

Important in tooth decay

It synthesizes a dextran capsule
- Dextran is a particular glycan synthesize by S. mutans

Promoted by high sugar diet becaue sucrose is ready source of glucose

Question 14

Polyglucose

Answer 14

Polyglucose = glycan - chains of glucose sugar

Question 15

Biofilms and Plaque

Answer 15

Much of the tooth surface is coated with salivary glycoproteins = a pecile

Some oral bacteria adhere to pellicle (ligan/adhesin receptor interaction)
- But some S.mutans can also adhere to tooth surface using dextran capsule

After adherence S.mutans grows and produces more dextran

Other bacteria become embedded in the forming biofilm

At some point the biofilm may became thick enough to be considered a plaque

Within the plaque, S.mutans and other bacteria ferment free sugars or those derived from polysaccharide digestion produces acidic waste products like lactic acid which causes tooth decay
- acid causes cavities in teeth

Question 16

To prevent colonization of infant in teeth

Answer 16

Mother and father should use a mouthwash that contains an attenuated strain of S.mutans for the baby

This displaces the type of product acids during fermentation - done before baby is born

The baby is then colonized with the bacteria that are in parents oral microbiota

Question 17

Respiratory Tract

Answer 17

The respiratory tract is very hard to study compared to other body sites
- it is hard to estimate the number of bacteria present

The mucosal epithelium of the upper R tract is colonized

The sinuses and lower R tract are normally, mostly, sterile

Sinuses infection are hard to treat, hard to deliver antibiotics

The mucociliary system of respiratory tract expels foreign articles

Mucus trapped material expelled by nasal discharge, coughing sneezing, swallowing into stomach acids
- cillia

Question 18

The microbiota of the upper R tract can still maintain presence despite the mucociliary system

Answer 18

People that smoke are more prone to respiratory infections

• Damage ciliated cells resulting in impared action of mucociliary system of respiratory tract
• But can be regenerated

People that abuse alcohol also are more prone to respiratory infections

• Aspiration of oropharyngeal secretions containing pathogens because the gag reflex is impaired
• Result in impaired action of the mucociliary system

Question 19

The Gastrointestinal Tract

Answer 19

There are many different environments within the gastrointestinal tract

Bacteria occupy both the lumen and the surface of the GI mucosal epithelium

Around 10^14 bacteria, mostly in the large intestine

On a human population basis, over 1000 bacterial species identified by culture dependent and independent methods

Question 20

The Gastrointestinal Tract

: stomach

Answer 20

In the mucus covering the gastric epithelium (pH ~5), fermentative bacteria normally live there.

• in gastric fluid: pH ~1-2, normally about 10 bacteria/mL

Dozens of different species have been identified using culture different and culture independent method

Question 21

The Gastrointestinal Tract

: Small intestine

Answer 21

moving downward through the small intestine, the pH increases to about 8

The liver secretes bile into the small intestine

• used to digest fat
• contain molecules called bile acids/salts

Question 22

Bile salts

Answer 22

Bile acids can diffuse into lipid bilayers and disrupt membranes
- Hydrophobic parts associates with lipid tails - Hydrophilic parts associates with water

Gram-negative bacteria have the less fluid outer membrane as protection, so are resistant to bile acids

Both G-and G+bacteria may make extracellular enzymes to degrade bile acids

Recall that the microbiota help us digest fats, absorb vitamins, and convert steroids into a form that is useable/absorbed by us

Question 23

The large intestine

Answer 23

Large intestine is basically an anaerobic fermentation chamber

There is 1000 obligate anaerobic bacteria for every 1 facultative anaerobic bacterium

Bacteria in the large intestine metabolize plant polysaccharides and human derived polysaccharides (polysaccharide portions of mucous glycoproteins) that humans cannot digest

They ferment the resulting sugars and the fermentation waste products are metabolized by cells of the intestinal villi
- colonic fermentation

The human body gets 10-20% of its energy from the bacterial waste products derived from the colonic fermentation

Question 24

Colon Microbiota

Answer 24

Endospores: Large proportion of the colon microbiota can form endospores, a kind of resting cell

Vegetative form: and active cellular form that is capable of reproduction

Resting form: A dormant cellular form, not dead, but not capable of reproduction

The purpose of endospore formation is to protect the genome until favorable nutritional conditions return

When a favorable nutritional environmental returns endospore germinationis triggered

When endospores are expelled from the colon by defecation, endospore formation is used by some of the colonic microbiota to survive outside of the colon until they can recolonize a new host

Question 25

Spore forming bacteria: Clostridium difficile

Answer 25

Gram + endospore forming bacterium

• found as a member of normal flora in the large intestine in healthy individual
• survives in the environment on inanimate objects like bed pans and toilet seats

Clostridium difficile infection is the most common acquired infection by patients during a hospital stay - Nosocomial infections

Question 26

Clostridium difficile

Answer 26

Antibiotics kill both pathogens and bacteria of the microbiota –they cannot distinguish between the two groups.

Antibiotic treatment disrupts the other bacteria that normally are living in the colon
and also prevent C. difficile from transforming into its active, disease causing bacteria form

C. Difficile germinate. In the growing form, it produces the toxins that inflame and damage the colon

Antibiotic-associated colitis is an infection of the colon caused by C. difficile
- severity varies

Question 27

Clostridium difficile infections

Answer 27

Most cases are mild and self-limiting, but more severe infections can lead to severe inflammatory conditions

C. difficile produces and enterotoxin and a cytotoxin –both are responsible for degradation of the gut mucosa, attraction of inflammatory cells, and diarrhea

Patients with severe C. difficile colitis may have:

• High fever
• severe diarrhea
• severe abdominal pain and tenderness

Complications can lead to perforation, peritonitis, and sepsis
- potentially fatal

Question 28

Treatment of C. difficile

Answer 28

correction of dehydration, electrolytes, and discontinuing the antibiotic that caused the problem

Switching to an antibiotic to eliminate the C. difficilealso sometimes works

Drugs that are used to stop the diarrhea (in other conditions) can make the disease worse

Stool transplants from a healthy donor (and tested for pathogens –viral, parasitic, bacterial), have helped in severe cases

Question 29

Urogenital tract

Answer 29

Urine and the urogenital tract are normally sterile as the urinary tract is flushed on a regular basis

However, the vagina and the distal 1 cm of the urethra harbor microbial organisms

Lactobacillus in Vagina

• protects pathogens by lowering pH to 4-5 (lactic acid)
• loss leads to urinary tract infection
• oral contraceptives, antibiotics, anti histamines and other medication can raise pH (bad)

The distal urethra contains predominantly skin bacteria