Enteric Bacteria

Question 1

function of microbiota in health

Answer 1

contribute to host health
- fermentation of carbohydrates
- SCFA production
- promotes Treg development
- converts primary bile acids to secondary
- vitamin B and K synthesis

Question 2

function of microbiota in presence of pathogen

Answer 2

provide colonization resistance

Question 3

colonization resistance

Answer 3

• promotes production of antimicrobial peptides, IgA, and GI mucus
• maintains tight junctions between epithelial cells
• niche preemption

Question 4

niche preemption

Answer 4

“good” bacteria occupies the available space and resources to prevent pathogens from growing and occupying the niche

Question 5

where is the microbiome located

Answer 5

gut
lungs
skin
vagina

most exist in the lumen and are separated from epithelial cells by a mucus barrier

Question 6

where are the main microbes located

Answer 6

in the colon and other sites of fermentation (rumen, cecum)

Question 7

what are the main microbes of the microbiome

Answer 7

bacteroidetes
firmicutes

Question 8

bacteroidetes

Answer 8

gram negative
anaerobic
rods

Question 9

firmicutes

Answer 9

gram positive
anaerobic or facultative anaerobes
rods

Question 10

dysbiosis

Answer 10

microbiota disruption that contributes to disease/signs of disease

caused by disease, poor diet, travel or stress, medications, and weaning

leads to loss of normal microbiome functions

Question 11

how do antibiotics contribute to dysbiosis

Answer 11

reduces diversity of the gut microbiome

Question 12

how to prevent dysbiosis

Answer 12

• only use medications when clinically indicated
• reduce stress
• maintain good diet

Question 13

how to treat dysbiosis

Answer 13

• prebiotics
• probiotics
• fecal microbiota transplant

Question 14

prebiotics

Answer 14

non digestible carbohydrates that support bacteroidetes and firmicutes

safe but not always efficacious

Question 15

probiotics

Answer 15

supplying live bacteria to replace lost microbiota

minimally regulated
species differences in probiotic requirements

Question 16

fecal microbiota transplant

Answer 16

replacing full microbiota with a healthy one from donor

may cause problems in immunocompromised animals

Question 17

what are the requirements for bacteria to cause disease

Answer 17

1. resources (niche)
2. ability to avoid or survive the immune system

must be able to overcome colonization resistance

Question 18

opportunistic pathogens

Answer 18

bacteria that are typically part of the normal microbiota and don’t cause disease in their normal location

ex. klebsiella, enterobacter, proteus, some E. coli

Question 19

how do opportunistic pathogens cause disease

Answer 19

bloom in normal location then spread to abnormal locations

do NOT use virulence factors

often antibiotic resistant – survive treatment with abx while others get eliminated

Question 20

what are 3 factors that allow opportunistic pathogens use to overcome host defenses

Answer 20

1. pre-existing infection by parasites/viruses
2. drugs
3. host factors

Question 21

how does pre-existing infection by parasites/viruses allow opportunistic pathogens to spread

Answer 21

causes immunosuppression and GI damage that leads to altered host immune system

opportunists are then able to take advantage of pre-established dysbiosis

Question 23

how do host factors allow opportunistic pathogens to spread

Answer 23

increased genetic risk (ex. SCID), stress, and poor nutrition all contribute to pre-established dysbiosis

Question 24

frank pathogens

Answer 24

bacteria that are able to provide their own resources/niche and ways of avoiding the immune system

NOT present in microbiome normally

Question 25

how do frank pathogens cause disease

Answer 25

uses VIRULENCE FACTORS

create their own niche by causing GI damage –> inflammation –> bacteria thrives off inflammation

Question 26

what are 3 factors that allow frank pathogens use to overcome host defenses

Answer 26

1. bloom to high levels
2. evade host immunity
3. damage host cells

Question 27

how does blooming to high levels allow frank pathogens to spread

Answer 27

overwhelms the host barriers and out-competes other bacteria by rapid replication or slow GI transit time

requires virulence factors to overcome colonization resistance

Question 28

what are mechanisms that frank pathogens use to evade host immunity

Answer 28

• survive in wide pH range
• motility to invade mucus barrier
• evade IgA binding (ex. antigenic variation)

Question 29

antigenic variation

Answer 29

changing surface antigen as the bacteria grows to avoid recognition by the immune system

Question 30

how do frank pathogens cause damage to host cells

Answer 30

1. binding to intestinal cells to cause direct damage (no virulence factors required)
2. toxin production (binding does not cause damage)

Question 31

non-invasive vs invasive bacteria

Answer 31

noninvasive: causes attaching and effacing lesions on intestinal cell surface

invasive: attach to cells then go intracellular - requires toxin secretion

Question 32

how do the toxins produced by frank pathogen cause damage

Answer 32

1. form pores - increase host cell permeability
2. disrupt adhesion or tight junctions - decreases barrier function
3. alter immune response or cell signaling