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3151 disinfect > disinfectant test > Flashcards

disinfectant test Flashcards

1
Q

Characteristics of disinfectants:

A

○ Materials used for elimination of microorg
§ Physical aspect (cleaning)
§ Biologic aspect (antimicrobial activity)

○ Diverse application and regulations
§ Medical, veterinary, food, industry
§ Various application methods
§ STATE regulations differ from country to country

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2
Q

Properties of ideal disinfectant

A

1) broad spectrum
2) fast acting (rapid)
3) not affected by environ (organic matter) compaitable with soaps
4) non toxic
5) surface compatibility (not corrode surfaces, materials)
6) residual effect on treated surfaces
7) odorless
8) economical
9) solubility (water –> be able to wash away)
10) cleaning properties
11) environ friendly

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3
Q

factors involved in activity of disinfectant

A

Factors linked with antimicrobial agents/ microorg
factors of physical, physiochem, chem environ

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4
Q

Factors linked with antimicrobial agents/ microorg

A

□ Nature of microorg

□ Physiological state of the microorg

□ Microbial communities and biofilms
Natural and acquired resistance

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5
Q

Physical, physiochem and chem environ of microorg

A

□ Conc
□ Temp
- Inactivate bact or destabilise disinfectant

□ Presence of organic matter
-Reduce disinfectants ability to target microog

□ Electrolytes
-Form complexes and ppt, less conc of disinfectant for microorg

□ Additives and excipients
-Synergistic

◊ Make activity of disinfectant stronger

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6
Q

synergistic effect of accelerated hydrogen peroxide

A

1) Surfactant (Alkali metal, ammonium salts, alkyl sulphate)
◊ Weakens cell mem/ DNA

2) organic acid (chelating agent, inactivate radicals)

3) emulsifier (prevent pdt separate)

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7
Q

bacterial growth measures _ against _

A

unit forming colonies (log) vs Time

1) lag phase
2) exponential phase
3) stationary phase
4) death phase

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8
Q

lag phase

A

□ Cells are not dormant, synthesis of RNA, enzymes –> for cell replication

□ Eg G phase in humans
-Bacteriostatic aims to make all bact at this phase (so they are unable to undergo cell replication)

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9
Q

Log or exponential phase

A

□ Cells doubling at constant rate
□ Slope indicates speed of process
- Replication, splitting into daughter cells (depends on strains, some take days vs hrs)

     - Some test need to wait a few days just to see and check the presence of diff bact colonies (contamination)
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10
Q

Stationary phase

A

□ Growth-limiting factors affect replication

□ Number of cell growth = number of cells die
- No more materials (proteins, energy) needed for replication
- Death from accumulated waste

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11
Q

Death phase

A

□ Cell death > cell replication
May be of comparable rate (slope) to B

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12
Q

Microbial inactivation kinetics:

A

kinetic parameters and models used to compare diff processing technologies for reduction of microbial pop

(rate constants, temp, electric field)

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13
Q

Rate constants:

A

eqn indicate change of microbial pop as a function of time

K: reaction rate constant (1st order)

§ Will always be decr/ changing for disinfectants
§ Shows the number of surviving microbials over time

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14
Q

Temp coefficients:

A

influence of temp on microbial pop inactivation

§ Z factor = thermal resistance constant of bact to temp (thermal resistance)
□ Spores have larger Z value, higher resistance to temp change, since they are adapted for reproduction
□ At certain level may not have any changes

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15
Q

Electric field:

A

intensity applied should be > THRESHOLD electric field intensity

§ Critical electric field intensity for target microorg

§ **theoretically should be able to inactivate bact
§ At certain level may not have any changes

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16
Q

METHODS FOR evaluation tests, interfering factors and criteria for activity

A

1) prep carriers
2) prep test org and inoculum (representive test)
3) inoculation, drying the transfer of carriers
4) exposure of dried inoculum to test sub/ control fluid (standard amt, duration)
5) neut of test sub and elution of test org (remove trace of disinfectant, by mem filtration)
6) dilution and recovery of test org (revive survivors)
7) count surviving test org, assess performance of test sub

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17
Q

classification of test can be by __

A

microorg

§ Bactericidal test (neg: outer mem// pos: peptidoglycan)
§ Mycobactericidal test (TB)
§ Sporicidal test – highly resistance to chemical agent
§ Fungicidal test (fungi, yeast)
Virucidal test

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18
Q

Test strains
(representativeness and reliability)

A
  • Test strains must be representative of environment or object for what the product is meant for (hosp: staph aureus, pseudomonas)
    • Broad spectrum of efficiency according to in-use environment
      Diff mechanisms and activity
  • Exposure time
    • Time, conc, pH, temp
    • Type and amt of microorgs
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19
Q

test strains (may include interferin sub)

A
  • Stimulate practical condition
  • Must be compatible with wide variety of organisms that may be used in testing
    ○ Proteins bovine ~~ organic microorg to remove
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20
Q

2 step method

A

2-step method:

1) In step 1 methods: aq suspension (mixture of bacteria and water)

2) Step 2 methods: bacteria + dirt (interfering sub)
i. Dried onto stainless steel discs
ii. Disinfectants tested to try and reduce bacterial numbers

21
Q

criteria for activity (endpt)

A

MIC
MEC
MRC
MBC
MSC

22
Q

MIC

A

(minimum inhibitory conc)
* Lowest conc to inhibit growth, bacteriostatic
Determined visually after standard incubation period (18-24h)

23
Q

MEC

A

(minimum effective conc)

  • Lowest conc of active ingredients at which product still effective
  • Lag phase
    • Arbitrary
24
Q

MRC

A

(minimum recommended conc)
* From manufacturer (takes into account mistake in dilution of disinfectant/ cleaning not done properly)
- At higher conc

25
Q

MBC

A

(minimum bactericidal conc)
* Lowest conc of antibacterial agent that cause a 3log 10 ~ 4 log10 reduction in number of surviving cells (compared to initial, after incubation - 18 to 24h)
- Minimum lethal conc: test can be used against any microbe

26
Q

MSC

A

(minimal selective conc)
* Or minimum conc of antimicrobial agent at which resistant strains have competitive advantage
* BENEFIT of bacterial growth > COST of carrying drug-resistance trait compared with non-resistant strains
- Must put conc far above this, to be able to remove nutrients, prevent growth

27
Q
  • Prep of inoculum
    • Neutralising or washing by mem filtration
    • Detection and count of survivors
A

3a) preparation of inoculum
* Inoculum = pop of microorg/ cells introduced in fermentation medium/ other suitable medium
* 1st stage of inoculum: inoculum taken from working stock culture
○ Initiate growth in suitable lq medium (sterile water)
○ Put strains selected onto carrier
○ Growth strain to initial microbial load

3b) neutralisation of washing by mem filtration
* Test sub is neutralised and eluted to start recovery step
* Mem filtration: permits processing of entire elute vol
○ More efficient removal of any residue of test sub

3c) counting of survivors
* Count CFU after cultivation and growth of test organisms in suitable medium (specific rate of growth)
Back calculation: compare to sample size

28
Q

Quantitative recovery of microorg

A
  • Known inoculum of microorg spotted on stainless steel surface
  • Dried under heat & ventilation
    • = stimulated contaminated surface

► Contact plate applied to recover microorg spotted
► Number of CFU on contact plate compare to CFU spotted
* Calc recovery rate
* Impossible to achieve 100% at drying step
- But as long as it is constant can alr (standardised)

29
Q

Size of sampling

A
  • Depends on means of detection
  • Outlined in order to standardised test
    • To be able to compare to other tests (that follow same guideline)
    • Improve reliability of test
30
Q

Subculture and revival of survivors
(time, temp, humidity, pH)

A
  • Microbes are recovered and plated on suitable medium – agar plates/ saline/ trysin broth
  • Growth conditions assessed before testing
    • Assess recovery rate
      - Ensure constant rate of bact growth to do counting
31
Q

classification based on type of test

A

1) suspension
2) carrier
3) in-use and filed test

32
Q

suspension test

A

□ Potential activity of disinfectant in conditions stimulating practice
□ Mix fixed vol of known dilutions of disinfectants + fixed vol of inoculum
- Define contact time (incubation)
- Culture for counting

□ 1 step method (aq susp mix)

33
Q

carrier test

A

□ Disinfectant potentials (bact, fungi, spore) for ___ Under conditions that stimulate the application
-Surface (glass, stainless steel, plastic)
-Instrument

□ Disinfectant directly dropped on carrier surface at room temp
-Carrier immersed in disinfectant dilution
- Disinfectant dispersed by SPRAYING/ AEROSOL/ DROP-BY-DROP

□ Evaluated activity varied according to application method
Different carrier/ substances/ medium

34
Q

In-use and field test

A

□ Test of disinfectant and procedure of application in field — HOSP
-Susp or carrier test

□ No endpoint: not quantitative approach to reduction of flora (NO RESIDUAL CONTAMINATION)

35
Q

categorisation based on standard used

A

1) AOAC
2) AFNOR
3) DGHM
4) dutch standard susp test

36
Q

eg interfering sub

A

bovine albumin
skimmed milk (stimulate protein contents)

+ excipients that will be used in final formulation (surfactant, buffer)

37
Q

hygiene handrub and handwash

A

□ Hygienic hand-rub
- Treatment of hands with antiseptic hand rub
-Broad spectrum and fast-acting
◊ No need persistent activity

□ Hygienic handwash
-Treatment of hands with antiseptic handwash and water
-Broad spectrum
◊ Les efficacious and act more slowly than hygienic handrub

38
Q

protocol of HH steps

A

Reduce transient flora without necessarily affecting resident skin flora (eliminate capability to transient pathogens from hands)

§ Hands experimentally contaminated with test organism to evaluate ability to reduce naturally present resident flora

§ Variation in protocol – make direct comparison IMPOSSIBLE — interpret based on guidelines used
□ Contamination of hands with test org before test
□ To contaminate finger or HANDS
□ Vol of hand hygiene pdt applied
□ Contact time

39
Q

Comparison: based on that the same time frame if given

A
  • which org is more affected?
  • there is different activity level in each microorg (due to the outer layer)

Can maybe do the test in a longer time
- see if inhibition achieved to the same level if given a longer time?

* Exposure time limited by practicality (disinfectant not stable in long time)
* resistance of org

Everything must be standardised so that comparison can be done

40
Q

importance of sample size

A

How big sample and the ratio b. test and interfering sub

41
Q

Ratio importance?

A

Disinfectant affected by organic matter
Must have known ratio

42
Q

Point of initial titer of virus

A

a. For back calculation from endpoint
i. Find log reduction of viral load
b. Measure recovery after drying step

43
Q

Why neutralising

A

a. Quenching (dilution/ neutraliser) – remove activity of formaldehyde
b. Filtration
i. Effective cessation of antiviral activity

44
Q

Role of incubation

A

a. For proper counting, otherwise presence of residual disinfectant will overestimating power of disinfectant
i. Decr growth of microbial
b. Presence of excess bovine (skimmed milk) can cause underestimation of disinfectant
i. Increased growth of microbial

45
Q

End-point

A

4 log reduction criteria

46
Q

importance of having Control

A

a. Assess no interfering of disinfectant in growth medium
b. Allow comparison to other test following same guidelines

47
Q

biofilms

A

microorg may be protected from disinfectants by production of thick masses of cells and Extracell materials or biofilms

48
Q

biofilm resistance by

A

1) physical layer of older biofilm
2) genotypic variation
3) microbial prod neutralising enzymes
4) physiologic gradients in biofilm

49
Q

treat biofilms with

A

A
chlorine compounds

ozone

resistant to drying, UV, antimicrobial (surfactants, AB, disinfectants)

3151 disinfect (6 decks)

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