Chapter 4 - B Flashcards
Locations of the microbiota include
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
Skin:
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
Skin
Secretions:
sweat
Sebum: oily waxy substances produced by sebaceous glands
- coats moisturize and protect skin
- Also contains lysozyme to break down pathogens
no mucous
Skin Microbiota:
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
We have more bacteria post-wash
Dead layer of skin is washed off and its the bacteria on the living skin surface that is picked up
Skin
Dry areas - less organism per area
Moist area - more organism per area
Skin environments that impact microbiota
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
Examples of Skin Microbiota:Propionibacterium acnes
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
Examples of Skin Microbiota: Staphylococcus aureus
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
Examples of Skin Microbiota: Staphylococcus epidermidis
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
Microbiota of the oral cavity
Gingival crevices anaerobic bacteria
tooth surfaces aerobic
On human population baes, hundreds of different species identifies by culture dependent and independent method
Microbiota of the oral cavity
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
Streptococcus mutans
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
Polyglucose
Polyglucose = glycan - chains of glucose sugar
Biofilms and Plaque
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
To prevent colonization of infant in teeth
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
Respiratory Tract
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
The microbiota of the upper R tract can still maintain presence despite the mucociliary system
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
The Gastrointestinal Tract
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
The Gastrointestinal Tract
: stomach
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
The Gastrointestinal Tract
: Small intestine
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
Bile salts
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
The large intestine
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
Colon Microbiota
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
Spore forming bacteria: Clostridium difficile
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
Clostridium difficile
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
Clostridium difficile infections
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
Treatment of C. difficile
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
Urogenital tract
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
