Normal Microbiota

Question 1

Which areas of the body tend to have a higher organism density?

Answer 1

moist or protected areas, such as the armpits or groin area dry, exposed areas of skin harbour fewer organisms

Question 2

Where in the body has the highest organism density?

Answer 2

the oral cavities and colon

Question 3

What is meant by normal flora/microbiota?

Answer 3

organisms found in a given location in a state of health

Question 4

What is meant by colonisation?

Answer 4

the establishment of microorganisms at a site in the body

Question 5

What is meant by microbiota?

Answer 5

all the organisms within a given community

Question 6

What is meant by the microbiome?

Answer 6

all the genes present within the microbiota

Question 7

What is meant by symbiosis?

Answer 7

when two or more organisms co-exist in close physical association

Question 8

What is meant by mutualism in symbiosis?

Answer 8

When both organisms involved benefit from symbiosis

Question 9

What is meant by neutralism in symbiosis?

Answer 9

When neither of the organisms involved derive benefit or harm from symbiosis

Question 10

What is meant by commensalism in symbiosis?

Answer 10

When one organism benefits and the other derives neither benefit nor harm

Question 11

What is meant by parasitism in symbiosis?

Answer 11

When one organism (parasite) benefits at the expense of the other (host)

Question 12

What is the difference between sterile and non-sterile sites in the body?

Answer 12

non-sterile sites have normal flora sterile sites have no normal flora

Question 13

What is significant about non-sterile sites?

Answer 13

They are exposed to the environment, either directly or indirectly There is no mechanism in place to maintain sterility

Question 14

What are the 5 main non-sterile sites?

Answer 14

1. conjunctiva 2. nasopharynx 3. GI tract 4. vagina 5. skin

Question 15

When does the acquisition of normal flora begin?

Answer 15

at birth until birth, sterility is maintained throughout

Question 16

How can blood cultures/CSF/ pleural fluid samples be contaminated?

Answer 16

they are obtained by passing a needle through the skin to the relevant sterile site there is potential for contamination with skin organisms

Question 17

How are sputum samples obtained? What is the problem with sterility?

Answer 17

obtained by expectoration of lower airways secretions (sterile site) through the upper airways (non-sterile site) there is a risk of contamination

Question 18

How are urine samples obtained? What is the problem with sterility?

Answer 18

obtained by passing urine from the bladder/upper urinary tract (sterile site) via the terminal urethra (non-sterile site) Risk of contamination

Question 19

How is the risk of contamination minimised when collecting a urine sample?

Answer 19

by collecting an MSU sample (mid-stream urine)

Question 20

What are the 3 ways in which sterility is maintained at sterile sites?

Answer 20

1. sterility maintained by surface cleaning 2. sterility maintained by barriers that allow unidirectional flow 3. sterility maintained by physical separation from non-sterile sites

Question 21

What are examples of areas where sterility is maintained by surface cleaning?

Answer 21

areas that are open to the environment such as the lower respiratory tract

Question 22

What are examples of areas where sterility is maintained by barriers?

Answer 22

areas that are adjacent to non-sterile sites e.g. the urinary tract is protected by the urethra

Question 23

What are examples of areas where sterility is maintained by physical separation?

Answer 23

any closed cavities e.g. spinal cord and meninges, pleural cavity

Question 24

What is meant by tissue tropism?

Answer 24

the propensity for a particular organism to grow in a particular habitat

Question 25

What are the 5 main physical variables that influence which organisms colonise which areas?

Answer 25

1. moisture 2. temperature 3. pH 4. O2 availability 5. nature of the surface

Question 26

Where are most bacteria found on the skin?

Answer 26

within the sweat glands

Question 27

What is the temperature, O2 levels, nutrient levels and characteristics of the skin?

Answer 27

1. variable temperature 2. dry and subject to abrasion 3. aerobic environment 4. nutrient-poor

Question 28

What is the temperature, O2 levels, nutrient levels and characteristics of the gingival crevice?

Answer 28

1. constant temperature 2. moist with few physical challenges 3. anaerobic environment 4. nutrient-rich

Question 29

What are the 3 most common skin flora?

Answer 29

1. coagulase-negative staphylococci 2. staphylococcus aureus 3. propionibacterium species

Question 30

What is the problem when analysing bacteria on the skin?

Answer 30

the bacteria on the skin near any body orifice may be similar to those within the orifice

Question 31

What are the typical flora found within the mouth?

Answer 31

viridans/oral streptococci anaerobes

Question 32

What are the typical flora found within the nostrils?

Answer 32

1. any of the skin flora 2. staphylococcus aureus - the nose is the main carrier site

Question 33

What is the problem if the respiratory tract epithelium becomes damaged?

Answer 33

any of the microorganisms present in the pharynx can cause infection in the lower respiratory tract

Question 34

What are examples of flora that are present within the pharynx?

Answer 34

1. streptococcus pyogenes 2. haemophilus influenzae 3. streptococcus pneumoniae 4. s. aureus 5. neisseria meningitidis

Question 35

What is the normal flora in the vagina pre-puberty?

Answer 35

1. any of the skin flora 2. lower GI flora - mainly E. coli

Question 36

What is the normal flora in the vagina post-puberty? Why does this change?

Answer 36

Glycogen is produced due to circulating oestrogens 1. lactobacillus acidophilus ferment glycogen 2. skin flora 3. a few C. albicans

Question 37

What is significant about lactobacillus acidophilus fermenting glycogen?

Answer 37

they maintain the pH of the vagina at 3 This prevents the overgrowth of other species An overgrowth of C. albicans causes thrush

Question 38

What are the typical flora found within the stomach and small intestine?

Answer 38

predominantly aerobic bacteria: 1. acid-tolerant lactobacilli 2. helicobacter pylori the low gastric pH inhibits bacterial growth

Question 39

How can H. pylori survive in the stomach despite the acidic pH?

Answer 39

it produces urease that converts urea into ammonia and carbon dioxide

Question 40

What are the normal flora found within the large intestine?

Answer 40

99% anaerobes such as: 1. bacteroides 2. clostridium 3. bifidobacteria The aerobic bacteria are enteric Gram-negative bacilli

Question 41

What mechanism prevents the overgrowth of pathogens within the large intestine?

Answer 41

colonisation resistance by the normal gut microflora

Question 42

How can the normal flora provide a health benefit through metabolism?

Answer 42

1. vitamins K and B12 are secreted by enteric bacteria 2. unused energy substrates are fermented to produce short-chain fatty acids

Question 43

What is the benefit of vitamin K production?

Answer 43

E. coli in the colon produce vitamin K It is essential for blood clotting and bone metabolism

Question 44

What are the benefits of butyrate (SCFA)?

Answer 44

it helps to prevent bowel cancer and modulates immune responses

Question 45

What are the benefits of propionate (SCFA)?

Answer 45

it promotes saiety it prevents lipid lipidogenesis it lowers cholesterol it provides anti-carcinogenic activities

Question 46

How can normal flora provide colonisation resistance?

Answer 46

Through environmental manipulation e.g. lowering the pH Through production of antibacterial agents e.g. bacteriocins

Question 47

In what other way can normal flora provide health benefits?

Answer 47

through induction of cross-reactive antibodies

Question 48

In general, in what 4 ways can SCFAs provide health benefits to the body?

Answer 48

1. help to inhibit enteropathogens 2. provide energy to epithelial cells/colonocytes 3. promote mucin production 4. affects gut hormone production and modulates appetite

Question 49

How can antibiotics negatively impact normal flora?

Answer 49

antibiotics kill off pathogenic organisms and normal flora this reduces the diversity which is key to the health benefits of the normal flora

Question 50

What is the main risk factor for clostridium difficile infection?

Answer 50

antibiotic treatment

Question 51

What is the background behind C. difficile infection?

Answer 51

perturbation of normal colonic microflora allows C. difficile overgrowth this leads to toxin production

Question 52

In what 3 ways may there be a pathology of the normal flora?

Answer 52

1. overgrowth 2. translocation 3. cross-infection

Question 53

What is meant by overgrowth of normal flora?

Answer 53

excessive growth at the normal site

Question 54

What is meant by translocation of normal flora?

Answer 54

presence of the normal flora at the wrong site this may be as they have been spread from one site to another

Question 55

What is an example of a condition caused by overgrowth of normal flora? What may have caused this?

Answer 55

thrush treatment with a broad spectrum antibiotic can lead to inhibition of colonisation resistance

Question 56

What is an example of a condition caused by translocation where normal flora have been moved from one surface to another?

Answer 56

conjunctivitis red eyes with purulent conjuctivital discharge following URTI with cough and runny nose

Question 57

What are typical clinical conditions caused by normal flora?

Answer 57

Question 58

Why is it often difficult to determine the clinical significance of the presence of normal flora in a sample?

Answer 58

The opportunity for sample contamination is high Organisms are often present in a sample benignly and are not the cause of symptoms