Normal Microbiota and the Host

Question 1

What are normal microbiota?

Answer 1

Permanently colonize the host.

Question 2

What are transient microbiota?

Answer 2

May be present for days, weeks, or months.

Question 3

What is symbiosis?

Answer 3

The relationship between normal microbiota and the host.

Question 4

What does symbiosis mean?

Answer 4

An association of two or more different species of organisms.

Question 5

What does symbiont mean?

Answer 5

Physical contact between dissimilar organisms.

Question 6

What are the 5 types of microbial interactions?

Answer 6

> symbiosis 
> symbiont
> ectosymbiont 
> endosymbiont 
> consortium

Question 7

True or False:

Several commensalism bacteria are opportunistic organisms.

Answer 7

True

Question 8

What is commensalism?

Answer 8

One organism benefits, and the other is unaffected.

e.g., Staphylococcus epidermidis on the skin

Question 9

What is mutualism?

Answer 9

Both organisms benefit.

e.g., E. coli in the large intestine

Question 10

What is parasitism?

Answer 10

One organism benefits at the expense of the other.

e.g., H1N1 virus particles on a host cell

Question 11

What is microbial antagonism?

Answer 11

Is a competition between microbes.

Question 12

What do normal microbiota doe for the host?

Answer 12

Protect the host by:
> occupying niches that pathogens might occupy.
> Producing acids.
> Producing bacteriocins.

Question 13

What is the microbiome?

Answer 13

> All the genes of the host and the microbiota.

> Goal is to determine the impact that micrboial gene function has on human health.

Question 14

What are superorganisms?

Answer 14

> Emerge when the gene-encoded metabolic processes of the host become integrated with those of the microbe.

> A blend of host and microbial traits where host and microbial cells cometabolize various substrates, resulting in unique products.

Question 15

What are germfree animals used for?

Answer 15

> Can be used to study effects of microbes on animal health by:

• comparing germfree animals to normal animals
• introducing a single microbe to the germfree animal and observing effects

> Born by cesarean section, raised in sterility.

> Can be coupled with genomic studies for maximum benefit.

Question 16

List the reasons to study normal human microbiota.

Answer 16

> to gain insight into possible infections resulting from injury.
to understand causes and consequences of overgrowth of microbes normally absent from a body site.
to increase awareness of role played by indigenous microbe in stimulating immune response.

Question 17

In which people are Bifidobacteria found?

Answer 17

> found in breast fed babies

> protrophic - can synthesize all amino acids and growth factors from from simple carbohydrates

Question 18

What are probiotics?

Answer 18

Live microbes applied to or ingested into the body, intended to exert a beneficial effect.

Question 19

How does normal microbiota protect the host?

Answer 19

By competing with pathogens or altering the environment:
> occupy niches that pathogens might occupy
> producing acids
> producing bacteriocins

Question 20

What are opportunistic pathogens?

Answer 20

Members of normal microbiota that produce disease under certain circumstances.

Question 21

What is a compromised host?

Answer 21

Debilitated host with lowered resistance to infection.

Question 22

What makes the skin an inhospitable environment?

Answer 22

> slightly acidic pH
high concentration of NaCl
many areas low in moistrue

Question 23

What is the normal microbiota of the skin?

Answer 23

> mechanically strong barrier
inhospitable environment
inhibitory substances (e.g., lysozyme)

Question 24

What organisms are normal microbiota of the skin?

Answer 24

> Gram-positive, salt-tolerant bacteria:

• Staphylococci (e.g., S. epidermidis)
• Micrococci (e.g., M. luteus)
• Diphtheroids
  
  • Aerobes on surface (e.g., Corynebacterium xerosis)
  • Anaerobes in hair follicles (Propionibacterium acnes)

> a few Gram-negative organisms (e.g., Acinetobacter)
Grow on oils:
- Yeast (Malassezia furfur) - causes dandruff

Question 25

What organism causes dandruff?

Answer 25

Yeast - Malassezia furfur

Question 26

What is acne vulgaris caused by?

Answer 26

Caused in part by activities of Propionibacterium acnes:
> Sebum
- fluid secreted by oil glands
- accumulates, providing hospitable environment for P. acnes

> Comedo

 - plug of sebum and keratin in duct of oil gland
 - results from inflammatory response to sebum accumulation

Question 27

Normal microbiota of the eye and external ear.

Answer 27

> Eye

• from birth throughout a human life, small numbers of bacteria commensals are found on the conjunctiva of the eye
• the predominant bacterium is Staphylococcus epidermidis

> External Ear
- similar to skin flora as well as fungi

Question 28

Normal microbiota of the oral and upper respiratory tract.

Answer 28

Oral bacteria are responsible for dental caries.
(e.g., S. mutans and Lactobacillus)

Mouth - contains organisms that survive mechanical removal by adhering to gums and teeth.
> contribute to formation of dental plaque, dental caries, gingivites, and periodontal disease.
Within hours of birth, the oral cavity is colonized by microorganisms from the surrounding environment.

Suppress pathogens by competitive inhibition in upper respiratory system.

> Staphylococcus aureus and S. epidermidis:

• predominant bacteria present
• found just inside nostrils

> Pharynx and trachea contain Gram-positive bacteria:

• Staphylococci (e.g., S. epidermidis)
• Micrococci (e.g., M. luteus)
• Streptococci (both alpha- and beta-hemolytic)

> Nasopharynx may contain low numbers of potentially pathogenic microbes:

• Streptococcus pneumoniae
• Neisseria meningitidis
• Haemophilus influenzae
• Mycoplasmas may also be found in pharynx

Question 29

Does the lower respiratory tract have a normal microbiota?

Answer 29

> No
Microbes moved by:
- continuous stream of mucous generated by ciliated epithelial cells (ciliary escalator)
- phagocytic action of alveolar macrophages
- lysozyme in mucus

Question 30

Stomach

Answer 30

> Most microbes killed by acidic conditions.

• some survive if pass through stomach very quickly
• some can survive if ingested in food particles

Question 31

Small Intestine

Answer 31

> Duodenum - contains few organisms
Jejunum
Ileum - flora present becoming similar to that in colon because the pH becomes more alkaline.

Question 32

True or False:

There are several organisms in the duodenum.

Answer 32

False - contains few organisms.

Question 33

Why does flora become more present in the ileum?

Answer 33

Flora present becoming similar to that in colon because the pH becomes more alkaline - not as acidic.

Question 34

What area in the body has the largest microbial population of the body?

Answer 34

Large Intestine (colon)

> eliminated from body by peristalsis, desquamation, and movement of mucus
replaced rapidly because of their high reproductive rate
most of the microbes present are anaerobes

Question 35

How many bacteria are there per gram of feces?

Answer 35

100 billion

Question 36

List the organisms found in the large intestine.

Answer 36

E. coli
Bacteroides
Fusobacterium 
Lactobacillus
Enterococcus 
Bifidobacterium 
Enterobacter
Citrobacter
Proteus 
Klebsiella
Candida (fungus)

Question 37

True or False:

The kidneys, ureter, and bladder are typically free of microbes.

Answer 37

True

Question 38

True or False:

Many microbes are found in the distal portions of the urethra.

Answer 38

False - few microbes found.

Question 39

What organisms are found in the female genital tract?

Answer 39

> complex microbiota in a state of flux due to menstrual cycle.
acid-tolerant lactobacilli predominate in vagina
- produce H202
- grow on glycogen secretions

> infection is indicated by:

• greater than 10,000 bacteria/ml
• 100 coliforms/ml
• positive urine leukocytes esterase (LE) test