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EOS Principles of diseases > microbial disinfection > Flashcards

microbial disinfection Flashcards

1
Q

in terms of microbial disinfection, what part of the bacterial growth curve do we aim to maximise?

A
  • aim to maximise the death or decline phase
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2
Q

define sterilisation

A
  • kills off all microorganisms (including spores)

- not an absolute state

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3
Q

define disinfection

A
  • is to kill, inhibit or remove pathogens to levels that prevent infection risk on inanimate objects & surfaces
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4
Q

define antisepsis?

A
  • is to kill, inhibit or remove pathogens to levels that prevent infection risk in skin, mucous membranes & tissues
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5
Q

define sanitation

A
  • is reducing microbes to a “safe” or “acceptable” level

- imprecise, non-scientific term

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6
Q

define asepsis

A
  • is the prevention of microbial contamination by excluding or removing microbes
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7
Q

define decontamination

A
  • is cleaning & disinfection
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8
Q

define biocidal

A
  • lethal to microbes by irreversible inhibition (bactericidal, virocidal, germicidal)
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9
Q

define biostatic

A
  • is the reversible inhibition of reproduction
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10
Q

what are the 2 ways that viability can be determined?

A
  1. direct identification & enumeration (direct count)

2. indirect indicators - presence of metabolic by-products

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11
Q

what are the limitations of viability measures for infectious organisms?

A
  • sensitivity, specificity & limits of detection for counts
  • for molecular methods - theres no differentiation between viable microorganisms vs presence
  • for serological methods - theres no differentiation between current infection vs a previous exposure
  • microbe could be viable but in a non-culturable state
  • death of a microbe can be difficult to define
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12
Q

when are microbes more susceptible to death by disinfectants?

A
  • microbes in the growth phase
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13
Q

what factors influence a microbe’s susceptibility to death?

A
  • stage of growth
  • clumping of cells
  • environmental conditions
  • microbial communities (protection)
  • specific strain variability
  • intracellular parasites
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14
Q

what are bacterial endospores? and what basis do they form?

A
  • is a survival mechanism used by some bacteria
  • bacteria that form endospores can remain dormant for decades & when environmental conditions become favourable, they become activated & germinate
  • endospores form the basis of sterilisation standards
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15
Q

how do viral envelopes affect susceptibility to disinfectants, heat & environmental degradation?

A
  • enveloped viruses are more susceptible to disinfectants, heat & environmental degradation than non-enveloped viruses
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16
Q

what is sublethal injury?

A
  • sublethal injury is a reversible state of injury where cell can recover in favourable conditions
  • is a viable but non-culturable state
  • increases susceptibility of death for these microbes
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17
Q

how are biofilms formed?

A
  • biofilms are formed when 3D bacterial communities attach to a surface
  • bacteria are embedded in an extracellular polymeric substance
18
Q

what are biofilms protected from?

A
  • physical removal
  • disinfectants, antiseptics & antibiotics
  • immune system
19
Q

name the 4 physical methods of disinfection

A
  1. heat
  2. ionising radiation
  3. gases
  4. chemicals
20
Q

when is dry heat used as a physical method of disinfection?

A
  • 160*C at 60-90mins
  • for porous solids (powders) & non-aqueous liquids
  • for items that cannot be subjected to moist heat as it is non corrosive
21
Q

when is moist heat used as a physical method of disinfection?

A
  • 100*C at 3 mins
  • more efficient compared to dry heat
  • most effective method is pressurised steam (autoclave)
  • autoclave kills bacteria, viruses & spores
  • pressurised steam allows water to store more energy to kill microbes
22
Q

define the decimal reduction time (D value)?

A
  • is the time it takes in minutes for a tenfold reduction in specified bacterial population at a specified temperature
  • 1 log reduction = 90% reduction of bacteria
  • D value extends below the x-axis, meaning absolute sterility is not possible
23
Q

define thermal death time (Z value)

A
  • is the temperature change required to change the D value tenfold (lower Z = more heat susceptible)
  • measures resistance to different levels of heat
24
Q

how does ionising radiation work as a physical method is disinfection? what are its pros & cons?

A
  • causes DNA damage & forms free radicals that are lethal to microbes
  • cons: space, cost, safety
  • pros: does not use heat or moisture, penetrates packaging which reduces risk of contamination after radiation treatment
25
Q

what are the applications of ionising radiation?

A
  • single use materials
  • medical materials (sutures, syringes)
  • pharmaceuticals
  • lab equipment
26
Q

what are the pros & cons of using alkalising gases as a physical method of disinfection?

A

pros

  • highly effective against a wide range of organisms
  • highly diffusible
  • can be used for heat sensitive material & electronics

cons

  • toxicity
  • corrosion, flammable
  • special equipment & facilities needed
27
Q

how is filtration used as a physical method of disinfection?

A
  • small pore sizes filter out different microbes

- 10nm needed for viral sterility

28
Q

what are 3 considerations for chemical methods of disinfection

A
  • material being disinfected
  • contamination with organic material
  • contact time required
29
Q

when are acids & alkalis used as a chemical method of disinfection? what are the benefits of using them?

A
  • used for large scale or industrial/commercial disinfection
  • cheap, readily available
  • resistant to organic matter
  • has detergent/cleaning action
  • effectively kills a range or microbes & biofilms
    but is corrosive
30
Q

when are alcohols used as a chemical method of disinfection?

A
  • mainly for skin disinfection
  • often used in conjunction with iodine or chlorhexidine
  • works better with 70% alcohol mixed with water
  • fast acting but short residual activity
31
Q

when are aldehydes used as a chemical method of disinfection?

A
  • used for heat-sensitive equipment & materials

- wide antimicrobial spectrum, highly effective but have some toxicity

32
Q

what are the benefits & limitations of using quaternary ammonium compound as a chemical method of disinfection?

A
  • is a general cationic surface-active disinfectant with cleaning action
  • prolonged contact time is possible
  • lower user & patient toxicity & irritability
  • inactivated by organic matter, hard water & soaps
  • low activity against gram negative bacteria
33
Q

how is chlorhexidine used as a chemical disinfectant?

A
  • 0.5% water solution is relatively non-irritant & can be used on skin & mucous membranes but not ears
  • 0.5% in alcohol is used for skin gels & rubs
  • good residual activity
  • best if 5-10min contact time
34
Q

what are the main benefits & limitations of chlorine?

A
  • wide pathogen range & is highly effective, including spores
  • cheap & accessible
  • inactivated by organic material
  • corrosive for stainless steel & fabrics
  • irritants esp mucous membranes
  • store & make fresh
35
Q

what is iodine commonly used for during chemical disinfection?

A
  • used for treat dips & anti fungal scrubs

- as it is effective against fungal infections, low irritant & effect against a wide range of organisms

36
Q

what are oxidising agents used for during chemical disinfection?

A
  • good for environmental application
  • per oxygen biocides have agriculture & industrial uses (low toxicity & corrosiveness, wide range & generally good effectiveness)
37
Q

why can disinfectants sometimes fail?

A
  • microbes can become resistant to the disinfectant
  • improper use (not fit for purpose, not made up correctly, insufficient contact time or excessive organic matter load)
  • most disinfectant failure is b/c of poor contact between pathogen & disinfectant
38
Q

what is disinfectant contamination and which disinfectants are susceptible to disinfectant contamination?

A
  • some organisms can grow & reproduce in disinfectants

- QATS, chlorhexidine & synthetic phenolics

38
Q

what is disinfectant contamination and which disinfectants are susceptible to disinfectant contamination?

A
  • some organisms can grow & reproduce in disinfectants

- QATS, chlorhexidine & synthetic phenolics

39
Q

how should carcasses be disposed of to prevent dead animals from being a source of decontamination?

A
  • carcasses require composting, deep pit burial or incineration

EOS Principles of diseases (12 decks)

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