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Medical and general microbiology > practical microbiology > Flashcards

practical microbiology Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

why is direct microscopic count hard

A

due to the size of bacterial cells

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2
Q

turbidity

A

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

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3
Q

what temp is used to achieve dry weight

A

100-108 degrees

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4
Q

dry weight is …….. of wet weight

A

20-30%

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5
Q

what does chemical estimate of cell number use

A

amount of ATP or protein

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6
Q

what is the number of CFUs used to estimate

A

the number of bacteria in the original sample

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7
Q

miles and msra

A

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.

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8
Q

what helps achieve dry weight

A

centrifuge

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9
Q

why are dilutions used

A

so you can count number of bacteria on plate

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10
Q

why do filamentous bacteria look the way they do

A

they can swarm

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11
Q

highly motile bacteria may produce

A

larger colonies due to larger bacterial spread

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12
Q

capsule ot rxopolysacchardies look

A

mucosal or glossy and are circular and raised

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13
Q

dry and and rough

A

“ground glass”

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14
Q

why are counter stains used

A

producesczntrasting background and also makes differentiation clear

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15
Q

example of a counter stain

A

Safranin

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16
Q

immersion oil used to

A

increase resolving power

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17
Q

difference in biochemical activity can identify

A

diff species

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18
Q

most common biochemical test

A

fermentation of sugars

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19
Q

why is it important to have a pure culture

A

no contamination from other strains that have the same biochemical processes

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20
Q

MRS

A

growth medium good for lactobacilli- mannitol

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21
Q

why is fermentation of sugar a good process of differentiation

A

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

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22
Q

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

A

they may have a diff genotype and antimicrobial susceptibility phenotype

23
Q

Ampicillin

A

B-lactam

24
Q

Kanamycin

A

aminoglycoside

25
Q

genes for resistance can be coded on by either the

A

chromosome or the plasmid

26
Q

QIA-prep

A

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

27
Q

heterofermentative

A

produces lactic acid and sugar

28
Q

how to calculate % wet bacterial biomass

A

total- pellet/ total x100

29
Q

turbidity

A

cloudiness

30
Q

why do we use buffers

A

to maintain pH and osmolarity. when used alone- standard

31
Q

accepted range of CFU on plate

A

30-300 CFU’s

32
Q

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

A

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

33
Q

why do you multiply by the degree of the dilution

A

so they are comparable

34
Q

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

A

to prevent cross-contaminantion

35
Q

why do we measure cell number at 600nm?

A

won’t kill the cells

36
Q

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

A

280 nm- absorb max UV light at this wavelength

37
Q

enumerating

A

counting

38
Q

TMTC

A

too many to count

39
Q

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?

A

yes, because diff bacteria grow best in diff environments

40
Q

GRAM +VE

A

purple- larger peptidoglycan level

41
Q

GRAM -VE

A

red

42
Q

what is used in gram staining

A

crystal violet iodide comple

43
Q

Mann Rugosa Sharpe (MRS) agar is

A

designed to favour growth of lacobacilli

44
Q

at <5.2 pH bromocresol is

A

yellow

45
Q

at >6.8 pH bromocresol is

A

purple

46
Q

MIC

A

minimum inhibitory concentration

47
Q

how MIC can be measured

A

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

48
Q

location of DNA in gel electrophoresis indicates

A

BP length

49
Q

endonuclease cut at a

A

specific DNA sequence

50
Q

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

A

diff enzymes need to metabolise lactose

51
Q

where would the sugar ribose be found?

A

RNA

52
Q

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?

A

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

53
Q

MRS stands for

A

mann rogues sharpe

54
Q

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

A

Lactobacillus, Streptococcus, Pediococcus and Leuconostoc.

Medical and general microbiology (36 decks)

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