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Microbiology > Detection and Disinfection > Flashcards

Detection and Disinfection Flashcards

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Biology 101 flashcards
1
Q

most assays for detecting bacteria growth rely on

A

culturing bacteria and obtaining a pure culture of a single species

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2
Q

diluting samples is used to

A

isolate single colonies

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3
Q

dilution streaking

A

streaking bacteria from a culture on a plate
flame between each streak
rubbing bacteria off the loop and onto the plate

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4
Q

pour plates

A

warm media is mixed with agar in tubes
sample is serial diluted in several tube
tube are then poured onto a petri dish

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5
Q

biochemical identification

A

once a pure culture is obtained, it can be tested for its biochemical properties
many tests are required to positively identify a bacteria

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6
Q

biochemical identification kits

A

kits can complete many biochemical tests in one sample
the pattern of positives and negatives is interpreted by software
can identify many species this way, but not all

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7
Q

MALDI-TOF MS stands for

A

Matrix-assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry

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8
Q

what is MALDI-TOF MS

A

-grow bacteria on a plate
-scrape some bacteria onto a plate and add matrix (an organic acid that absorbs the laser)
-vaporize with an ultraviolet laser
-measure the mass to charge ratio of the resulting debris by the length of time it takes to reach the detector
-every bacterial species yields a specific pattern of debris
-spectrum can be matched to a database

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9
Q

how can antibodies be used as diagnostic tools

A

inoculating rabbits, mice, etc., with viral or bacterial antigens

the antibodies can be purified from blood, or produced in mass quantities recombinantly

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10
Q

advantages of diagnosis by antibodies

A

highly specific
rapid
point of care testing can be done cheaply

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11
Q

limitations of antibodies

A

expensive to generate, slow to develop (months)
antigenic variation can alter epitopes

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12
Q

ELISA

A

enzyme-linked immunosorbent assay

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13
Q

quantitative assay

A

the amount of colour change indicates the amount of antigen present

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14
Q

what is ELISA

A

-well is coated with an antibody for a specific antigen
-sample is added and incubated for antigens (virus or bacteria protein) to bind to antibody
-a detection antibody is added, which is conjugated to an enzyme that can process a substrate to generate colour change

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15
Q

lateral flow assay

A

COVID rapid antigen test
-liquid with sample rehydrates the reagents on the strip/pad/cassette
-capillary action wicks the samples and reagents across the Test Line (antibodies specific for antigen e.g., viral nucleoprotein)
-the negative control line has antibodies that recognize the detection antibodies

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16
Q

version of lateral flow assay

A

UTIs, streptococcus A, RSV, human chorionic gonadotropin (pregnancy)

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17
Q

genetic detection: nucleic acid amplification test (NAAT)

A

sequence-based surveillance and diagnosis
-highly specific
-inexpensive and fast
-flexible requirement for sample quality
-easily multiplexed (many tests in parallel)
-algorithms to correlate gene presence and pathogenicity
-less susceptible to variation in sequence than antibodies (target conserved regions)

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18
Q

newer assays can detect and determine

A

the sequence of all the nucleic acid in a sample
you can find things that you are not looking for and that no one has ever seen before

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19
Q

polymerase chain reaction (PCR)

A

a method to amplify specific segments of DNA into very large quantities

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20
Q

what was the main advance that allowed PCR

A

the discovery of thermostable polymerases from bacteria living near hydrothermal vents

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21
Q

PCR requires

A

buffer
Taq Polymerase (or variant)
Template/target DNA
dNTP (ATP, CTP, GTP, TTP)
Mg2+
Primers (~20 bp) which provide specificity and a free 3’OH
thermocycler

22
Q

detecting PCR products gel electrophoresis

A

gel electrophoresis - PCR products are added to well in an agarose gel
-gel is submerged in buffer
-current is run through the gel (DNA is negatively charged, moves towards the anode (+))
-PCR products are separated by size
-DNA can be visualized using intercalating dye e.g., Ethidium Bromide, which fluoresces under UV light
-laborious and not done often anymore in clinical labs

23
Q

real time, quantitative PCR

A

-PCR is conducted with a molecule that only fluoresces when it’s bound to double-stranded DNA
-assay is run in a thermocycler that has a camera and records the amount of fluorescence in each well at the end of each cycle
-the cycle where the fluorescence reaches a certain threshold can be used to calculate the amount of starting material
-can also be used with reverse transcriptase to convert RNA into DNA before amplification

24
Q

next-generation or deep sequencing

A

-PCR methods requires primers, which requires knowledge of the sequence being amplified
-new sequencing techniques can be used to obtain the entire nucleotide sequence of a sample without primers or foreknowledge
-can diagnose unknown pathogens, discover new variants, and be used to map pandemics
-used during the SARS-CoV-2 pandemic

25
Q

for use on fomites

A

disinfection
sanitization
sterilization

26
Q

for use on living tissue

A

antisepsis
degerming
aseptic

27
Q

disinfection

A

reduces or destroys microbial load of an inanimate item through application of heat or antimicrobial chemical

cleaning surfaces like lab benches, clinical surfaces and bathrooms

chlorine black, phenols (Lysol), glutaraldehyde

28
Q

sanitization

A

reduces microbial load of an inanimate item to safe public health levels through application of heat or antimicrobial chemicals

commercial dishwashing of eating utensils, cleaning public restrooms

detergents containing phosphates, industrial strength cleaners

29
Q

sterilization

A

completely eliminates all vegetative cells, endospores, and viruses from an inanimate item

preparation of surgical equipment and of needles used for injection

pressurized steam, chemicals, radiation

30
Q

antisepsis

A

reduces microbial load on skin or tissue through application of an antimicrobial chemical

cleaning skin broken due to injury, cleaning skin before surgery

boric acid, isopropyl alcohol, hydrogen peroxide, iodine

31
Q

degerming

A

reduces microbial load on skin or tissue through gentle to firm scrubbing and the use of mild chemicals

handwashing

soap, alcohol swap

32
Q

aspetic

A

an environment or procedure free of pathogenic contaminants

surgical field, handwashing, flame in a lab

33
Q

how do you kill or inactivate a microbe

A

physical methods: heat, filtration, desiccation, salt, radiation, refrigeration

chemical methods: damage the physical structure of the viruses, parasites, and viral particles

34
Q

effectiveness of killing or inactivating a microbe depends on

A

-population size
-population composition
-access of the agent to the microbe
-concentration of the agent
-duration of exposure
-local environment

35
Q

most resistant to most susceptible microbes

A

prions
bacterial endospores
cysts of Cryptosporidium
mycobacteria
cysts of other protozoa
small nonenveloped viruses
active-stage protozoa
fungal spores
most gram-negative bacteria
vegetative fungi
large nonenveloped viruses
most gram-positive bacteria
enveloped viruses

36
Q

microbial populations are not killed ______, they die ______

A

instantly
exponentially

37
Q

decimal reduction time

A

the amount of time to kill 90% of organisms at a given temperature

38
Q

what is the pressure canner temperature

A

121 degree C

39
Q

autoclaves

A

-generate high pressure saturated steam to sterilize equipment or solutions
-maintain a temperature of 121C at 15 psi for 15 minutes to eliminate spores
-indicator tape can be used to demonstrate that chamber reached the needed temperature for enough time

40
Q

sterility indicators

A

spore test

after autoclaving, flexible vial is squeezed to break ampule and release medium onto spore strip
yellow = not sterile
red = sterile

41
Q

methods of physical control of bacteria

A

dry heat sterilization: 160C, 2-3 hrs
pasteurization: 63C, 30 min or 72C, 15s, only reduce bacterial population, spores and some bacteria are still present
refrigeration: <4C, only stop/slow growth; many bacteria still viable, viral particles stabilized, freezing can kill some bacteria
salt: creates hypertonic solution, drawing water out of bacteria
desiccation: completely drying out a surface will kill bacteria, but not spores
radiation: causes damage to DNA, UV lamps sterilizes surfaces or water, ionizing radiation used to sterilize sutures or syringes
filtration: bacteria are >1 um, filtering with a 0.2 um or 0.1 um filter excludes most bacteria and many virus particles, useful for solutions that cannot be heated, important for control of pathogens in air

42
Q

HEPA filters in biological safety cabinets

A

High-Efficiency Particulate Arresting air filters remove 99.97% of all particles greater than 0.3 um from the air that passes through
-laminar flow of air prevents aerosol from leaving the cabinet through the front
-required to work with most pathogens in a lab

43
Q

N-95s

A

remove at least 95% of particles greater than 0.3 um from the air that passes through
-must be properly fitted
-not effective against smaller particles

44
Q

surgical masks only

A

block droplets and spit
they do not filter out small particles that can contain viruses

45
Q

generally, chemical control of microorganisms involves

A

substances that denature proteins or disrupt the plasma membrane

46
Q

chemical methods of disinfection

A

phenols
alcohols
halogens
heavy metals
quaternary ammonium compounds

47
Q

phenols or phenolics

A

original surgical soap, Lysol
-disinfectant
-denatures proteins, disrupts cell membranes
-remains active on surfaces
-smell bad and can cause skin irritation

48
Q

alcohols

A

isopropanol, ethanol
-disinfectant and antiseptic
-denatures proteins, dissolves cell membranes
-evaporate quickly

49
Q

halogens

A

iodine and chlorine
-disinfectant (chlorine) or antiseptic (iodine)
-oxidizing cellular material, likely denature proteins
-e.g., Bleach (sodium hypochlorite) and Betadine (Povidone-iodine)

50
Q

heavy metals

A

copper, silver, arsenic
-complex with and inactivate or denatures proteins
-copper handles, or water jugs can limit bacteria growth
-e.g., 1% Silver nitrate solution for eye gonorrhea

51
Q

quaternary ammonium compounds (quats)

A

cationic detergents
-disinfectant
-denatures proteins, disrupts cell membranes

Microbiology (11 decks)

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