Microbiology - Normal Flora

Created by tandoorifromage 

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Define Normal Flora:

Bacteria (including mycoplasma), yeast, and protozoans which inhabit the skin and mucosa of healthy persons
10^13 cells; 10^14 bacteria

What are three characteristics of normal flora:

1. Resident -- what you expect
2. Transient -- edging towards pathogenic, high turnover rate (e.g. S aureus)
3. Usually commensal -- (you are food and shelter !)

Normal Flora are non-pathogenic - True or False?

False NF does not mean non-pathogeic

80% of the dry weight of the GI tracts = Normal Flora - True or False?

True

Concept that bacteria go where they compete and stick best:

Tropism

Bacteria are not essential to life- True or False?

True -- germ free animals do fine

Why is it that highly invasive bacteria causes diarrhea in adults but not in newborns?

This exhibits the idea that specificity of receptors on cells changes with age --- newborns have yet to develop the associated receptor

What is bacterial interference?

1. Bacteria compete for binding sites
2. Compete for nutrients
3. Elaborate antibacterial factors vs. pathogens

NF compete with pathogenic bacteria

What benefit do NF provide?

1. Metabolism in the GI tract (b/d nutrients for absoprtion)
2. Stiulation of GI and other mucosal immune sites, cells, systems (i.e. priming of innate and adaptive immunity)
3. Development of cross reactive, protective antibodies on surface of bacteria

Loss of normal flora often leads to what?

1. Sites for pathogen adherence
2. Absence of interference allows replication after adherence
3. Skin, respiratory, GI and GU mucoae all are susceptible to adverse effect

INCREASED SUSCEPTIBILITY TO INVASION BY PATHOGENS

How can normal flora be potential pathogens?

If they penetrate the mucosa that they are living in --- can change the local environment -- causing disease


EX: adherence to perineal and vaginal surface --> UTI
Skin trauma introduces bacteria -- especially transient NF such as S. aureus -- to new adherence sites.

What are the 4 determinants of NF?

1. Age
2. Menstrual status
3. Environment (temperature, humidity)
4. Diet/nutritional state

What NF is common to the nose (skin and mucosa)?

1. Corynebacterium spp
2. S. epidermidis (resident)
3. S. aureus (transient)
4. Streptococci

What NF is common to the oral mucosa?

1. alpha hemolytic streptococci
2. gram negative anaerobic bacilli, facultative cocci, actinomycetes (dental plaques), protozoans, and candida (fungus) **** more likely to cause problem

NF of pharynx:

Alpha streptococci, gram negative anaerobic bacilli, and cocci, gram positive anaerobic occic, haemophilus spp, actinomycetes

EXCEPT TRACHEA --- = sterile except in chronic lung disease; should not have bacteria below larynx except in smokers

NF of stomach?

Normal acid level --> very few --- primarily streptococci and lactobacillus (unlikely to infect, but perhaps inflammation)

Low acid level -- MANY ORGANISM -- higher density, increased yeast -- starts to look like small bowel

There is increasing density of NF as you move more distally in the small bowel - True or False?

True --- enterococci, facultative gram negative bacilli, anaerobic bacteria the further you go

Perforation to distal bowel results in disease dominated by what?

Anaerobes --- (Anaerobic bacteria exist further down in bowel)

NF of the colon?

Favorable spot for anaerobic gram negatives and gram positives

10^11/g ... >150 identified strains

Anaerobic gram positive bacilli, anaerobic gram negative bacilli, facultative gram negative bacilli, enterococci

E. Coli -- 2-4% --- high turnover

What is the ratio of anaerobic to facultative bacteria within the colon?

100:1

What is the NF of the vagina?

Vagina is most sensitive to need for NF to maintain mucosal health

Lactobacilli (pH <4.5 maintained)

Changes with time

Group B streptococcus during reproductive time = transient NF

What is the NF of the bladder?

NONE -- it is sterile

What is the NF of the urethra?

--- small numbers of perineal and cutaneous organisms

Kept in check by normal urine flow

Urinary function impairment = PROBLEMO

When do NF become pathogens?

Most NF are intrinsically non-invasive in situ and in normal host.

Transient NF are more likely to be pathogenic with a little push.

1. Trauma to Mucosa
2. Bronchogenic aspiration
3. Perforation of GI mucosa or bowel

Nose is a source of what NF that can become pathogenic?

S. aureus

Trauma, Injury, and penetration of the oral mucosa are associated with what consequences?

1. Dental trauma -- > hemoyltic strep --> bacteremia, endocarditis
2. Penetration --> polymicrobial necrotizing infection and abscess
3. Injury (by another infectious disease)--> abscess, tonsilar

What happens with aspiration of oral flora?

Pneumonia (inflammation of the lungs) or lung abscess (destruction of tissue and replacement by white blood cells

GI perforation

How can you mess up the NF?

Antibiotics -- decrease bacterial interference allowing:
1. Attachment of pathogens (respiratory mucosa, skin)
2. Replication of pathogens (GI)
3. Loss of protective pH (vagina)
4. Increased susceptibility to enteric pathogens like salmonella, etc.
5. The clostridium difficult problem (lose colon's function to absorb water)

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