9. Normal Microbiota

Question 1

which areas of skin harbour more organisms?

Answer 1

moist, protected areas of skin, eg. armpits, groin or between the toes

Question 2

in which parts of the body is organism density the greatest?

Answer 2

oral cavities and colon

Question 3

what are normal flora?

Answer 3

organisms found in a given location in a state of health

Question 4

what is colonisation?

Answer 4

establishment at a site in the body

Question 5

what is symbiosis?

Answer 5

2 or more organisms co-exist in close physical association

Question 6

what is mutualism?

Answer 6

both organisms benefit from the symbiosis

Question 7

what is neutralism?

Answer 7

neither organism derives benefit or harm from the symbiosis

Question 8

what is commensalism?

Answer 8

one organism benefits, the other one neither benefits nor is harmed

Question 9

what is parasitism?

Answer 9

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

Question 10

what are non sterile sites?

Answer 10

sites with normal flora, are exposed to the environment either directly or indirectly, and have no mechanism in place to maintain sterility

Question 11

what are sterile sites?

Answer 11

those with no normal flora

Question 12

when do humans acquire flora?

Answer 12

at birth

Question 13

what are the 3 types of sterile sites?

Answer 13

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 14

where is sterility maintained by surface cleaning?

Answer 14

those places that are open to the environment

efficient cleaning by ciliated epithelium, removal of bacteria by coughing, sneezing or swallowing

Question 15

where is sterility maintained by barriers that allow unidirectional flow?

Answer 15

adjacent to non sterile sites eg. cervix and upper genital tract, urethra before urinary tract

Question 16

where is sterility maintained by physical separation from non sterile sites?

Answer 16

close cavities eg. plural and peritoneal cavities, meninges

Question 17

what factors influence what organisms colonise in which areas?

Answer 17

moisture
temperature 
pH
oxygen availability
nature of surface

Question 18

skin flora

Answer 18

coagulase -ve staph. eg. staph epidermis
staph aureus
propionibacterium acnes
the bacterium on the skin near any body orifice may be similar to those in the orifice

Question 19

mouth flora

Answer 19

viridian’s/oral streptococci

anaerobes

Question 20

what is the benefit of colonising in the mouth?

Answer 20

gain of nutrients, also provide the host with essential vitamins, synthesises by bacterial species
established normal flora can prevent colonisation of pathogenic flora

Question 21

nasopharyngeal flora - nostrils

Answer 21

skin flora

Staph aureus

Question 22

nasopharyngeal flora - pharynx

Answer 22

step. pyogenes
haemophilus influenzae
step. pneumoniae
Neisseria meningitidis
S. aureus

Question 23

vaginal flora - pre-puberty

Answer 23

skin flora

lowe GI flora, mainly E. coli

Question 24

vaginal flora, prost puberty

Answer 24

lactobacillus acidophilus
skin flora
C. albicans

Question 25

why is there a difference in flora in the vagina pre and post puberty?

Answer 25

circulating oestrogen at puberty stimulates production of glycogen in the vagina. lactobacillus acidophilus ferment the glycogen and maintain a oH of 3, preventing overgrowth of other species

Question 26

GI tract - stomach and small intestine flora

Answer 26

acid tolerant lactobacilli, H. pylori

due to inhibition of bacterial growth by low pH. predominantly aerobic becteria

Question 27

Gi tract flora - large intestine

Answer 27

95-99% anaerobes
bacteroides, clostridium, bifidobacteria
aerobic bacteria
gram -ve bacilli
E. coli, Klebsiella, enterobacter, proteus, citrobacter

Question 28

what are the benefits of normal flora?

Answer 28

1. synthesis and excretion of vitamins, eg. via K and B12 secreted by enteric bacteria
2. colonisation resistance by environmental manipulation and production of antibacterial agents
3. induction of cross-reactive antibodies may have a protective effect

Question 29

how can normal flora become pathogenic?

Answer 29

1. overgrowth, e.g vaginal thrush
2. translocation - presence on the wrong site - eg. through spread or inoculation
3. cross-infection eg. MRSA