practical microbiology

Question 1

why is direct microscopic count hard

Answer 1

due to the size of bacterial cells

Question 2

turbidity

Answer 2

Optical density- absorbance is proportional to cell number and weight. Colorimeter or spectrophometer.

Question 3

what temp is used to achieve dry weight

Answer 3

100-108 degrees

Question 4

dry weight is …….. of wet weight

Answer 4

20-30%

Question 5

what does chemical estimate of cell number use

Answer 5

amount of ATP or protein

Question 6

what is the number of CFUs used to estimate

Answer 6

the number of bacteria in the original sample

Question 7

miles and msra

Answer 7

splits plate into grids- smaller volumes used. Means more than 1 dilution can be plated per petri dish. however harder to count bacteria- has to be well labeled.

Question 8

what helps achieve dry weight

Answer 8

centrifuge

Question 9

why are dilutions used

Answer 9

so you can count number of bacteria on plate

Question 10

why do filamentous bacteria look the way they do

Answer 10

they can swarm

Question 11

highly motile bacteria may produce

Answer 11

larger colonies due to larger bacterial spread

Question 12

capsule ot rxopolysacchardies look

Answer 12

mucosal or glossy and are circular and raised

Question 13

dry and and rough

Answer 13

“ground glass”

Question 14

why are counter stains used

Answer 14

producesczntrasting background and also makes differentiation clear

Question 15

example of a counter stain

Answer 15

Safranin

Question 16

immersion oil used to

Answer 16

increase resolving power

Question 17

difference in biochemical activity can identify

Answer 17

diff species

Question 18

most common biochemical test

Answer 18

fermentation of sugars

Question 19

why is it important to have a pure culture

Answer 19

no contamination from other strains that have the same biochemical processes

Question 20

MRS

Answer 20

growth medium good for lactobacilli- mannitol

Question 21

why is fermentation of sugar a good process of differentiation

Answer 21

production of lactic acid will change the pH and this can be measured.

Question 22

although two e.coli may appear identical by gram stain and colony morphology

Answer 22

they may have a diff genotype and antimicrobial susceptibility phenotype

Question 23

Ampicillin

Answer 23

B-lactam

Question 24

Kanamycin

Answer 24

aminoglycoside

Question 25

genes for resistance can be coded on by either the

Answer 25

chromosome or the plasmid

Question 26

QIA-prep

Answer 26

isolation of u to 20ug of high purity plasmid or cosmic DNA- can be used in the process of sequencing

Question 27

heterofermentative

Answer 27

produces lactic acid and sugar

Question 28

how to calculate % wet bacterial biomass

Answer 28

total- pellet/ total x100

Question 29

turbidity

Answer 29

cloudiness

Question 30

why do we use buffers

Answer 30

to maintain pH and osmolarity. when used alone- standard

Question 31

accepted range of CFU on plate

Answer 31

30-300 CFU's

Question 32

is measuring biomass and turbidity a good quantitative method of enumerating bacteria in the probiotic same?

Answer 32

no- measures dead and alive cells- we are only interested in alive cells

Question 33

why do you multiply by the degree of the dilution

Answer 33

so they are comparable

Question 34

why is it important to change the tip between each serial dilution?

Answer 34

to prevent cross-contaminantion

Question 35

why do we measure cell number at 600nm?

Answer 35

won't kill the cells

Question 36

what wavelength of light would we use to measure protein or DNA?

Answer 36

280 nm- absorb max UV light at this wavelength

Question 37

enumerating

Answer 37

counting

Question 38

TMTC

Answer 38

too many to count

Question 39

based on the ops obtained from the biomass and turbidity experiments compared with the viable count (CFs), was there a diff between samples? Why would this be?

Answer 39

yes, because diff bacteria grow best in diff environments

Question 40

GRAM +VE

Answer 40

purple- larger peptidoglycan level

Question 41

GRAM -VE

Answer 41

red

Question 42

what is used in gram staining

Answer 42

crystal violet iodide comple

Question 43

Mann Rugosa Sharpe (MRS) agar is

Answer 43

designed to favour growth of lacobacilli

Question 44

at <5.2 pH bromocresol is

Answer 44

yellow

Question 45

at >6.8 pH bromocresol is

Answer 45

purple

Question 46

MIC

Answer 46

minimum inhibitory concentration

Question 47

how MIC can be measured

Answer 47

using a micro broth dilution method. identical amount of bacteria is put in each well, but trying conc of antibiotic- higher turbidity indicates more resistance- more bacteria

Question 48

location of DNA in gel electrophoresis indicates

Answer 48

BP length

Question 49

endonuclease cut at a

Answer 49

specific DNA sequence

Question 50

if all species metabolise glucose, why do some only partially ferment lactose, which is a milk sugar?

Answer 50

diff enzymes need to metabolise lactose

Question 51

where would the sugar ribose be found?

Answer 51

RNA

Question 52

mannitol s a product of heterofermentative metabolism carried out by a class of lactic acid bacteria. Why do only small groups of bacteria from yoghurt ferment mannitol?

Answer 52

mannitol can inhibit the growth of some bacteria, instead of encouraging it

Question 53

MRS stands for

Answer 53

mann rogues sharpe

Question 54

MRS Agar and Broth were designed to encourage the growth of the `lactic acid bacteria' which includes species of the following genera:

Answer 54

Lactobacillus, Streptococcus, Pediococcus and Leuconostoc.