Controlling contamination Flashcards

contam of medicals intro to sterilisation moist heat other techniques controlling processes Calculations sources of contam disinfectants

1
Q

What are the 4 medical relevencies of biofilms?

A

Majority of infections involve cells growing in biofilms
Indwelling medical devices
Growth on surfaces in e.g hospitals
Biological liquid systems (e.g. dialysis equipment)

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2
Q

What is bacterial sporulation?

A

Survival strategy when nutrients become exhausted
Mechanism used by some Gram-positive bacteria
Spores are very resistant to heat, radiation, desiccation and chemical agents
Can survive for many years

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3
Q

What are the two main consequences of microbial contamination?

A
  • Health hazard
    Contaminating organism or its toxins can cause disease
  • Spoilage
    Therapeutic breakdown of actives, or another component of formulation
    Might lose aesthetic appeal →Non compliance
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4
Q

What are the 8 classes of agents used as preservatives in the UK?

A

Organic acids
Parabens
Aromatic alcohols
Substituted alcohols
Biguanides
Mercurials
Substituted phenolic agents
Quaternary ammonium compounds

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5
Q

Which are the 2 preservatives used in oral products?

A

Organic acids
Parabens

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6
Q

Why are organic acids and esters preferred?

A

Organic acids
- limited by pH dependence;
- work at pH values up to pKa

Parabens
- overcome pH dependence of organic acids
- Active at low concentrations.
- Non toxic, cheap, stable.
- Reasonable spectrum of activity
- bactericidal, fungicidal (not sporicidal)
- Physically undetectable

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7
Q

How are preservatives evaluated?

A
  • suspension test
  • criteria of acceptance
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8
Q

What are the 5 factors affecting choice of any preservative?

A
  • Intended application
  • No. & type micro-orgs present
  • Safety, stability & Cost
  • Micro-environment
  • Properties of chemical agent
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9
Q

What are the two sterility probablities?

A

Sterility Assurance Level (SAL)
Probability of a Non-Sterile Unit (PNSU)

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10
Q

What is the minimum standard PSNU required?

A

For most pharmaceutical products, the minimal required standard is a PNSU of 1 in 106

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11
Q

What are the three sterilisation processes?

A

Destruction - e.g. flaming, chemical oxidation
- not practical for pharmaceutical products

Killing/inactivation
- used in most official methods
- may not remove endotoxins

Removing
- filtration, centrifugation

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12
Q

What is moist heat sterilisation?

A

Involves steam, usually at 121-134C
Very effective
Widespread application
Used for dressings etcs

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13
Q

What is dry heat sterilisation?

A

Usually in the range of 160-180oC
Less effective than moist heat sterilisation
Used for glass and metals etc

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14
Q

What is radiation sterilisation?

A

Sterilisation using gamma rays, accelerated electrons, X rays or UV
Alternative method for heat-sensitive products
Mainly for articles in dried state, e.g. plastic syringes, dry pharmaceutical products etc.

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15
Q

What is gaseous sterilisation?

A

Uses ethylene oxide or formaldehyde
Not same sterility assurance as heat - only used for heat sensitive items
Mainly for reusable surgical instruments, medical/diagnostic equipment, surface sterilisation of powders

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16
Q

What is filtration?

A

For sterilisation: 0.2-0.22µm filters used
The only process that removes microorganisms
Also used for removal of particulates, both from gases and liquids
For heat sensitive injections, ophthalmic preparations, biological products, and air and other gases for supply to aseptic areas

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17
Q

Which 4 factors used to choose sterilisation?

A
  • stability and nature of product
  • scale of production
  • type and level of contamination
  • cost
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18
Q

What is the D value?

A

decimal reduction time: time needed to reduce population by a factor of 10
t2 - t1
———–
logN1 - logN2

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19
Q

What is the Z value?

A

increase in temperature needed to reduce the D-value 10 fold
T2 - T1
———–
logD1 - logD2

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20
Q

What is autoclaving?

A

Moist heat with temp >100oC can only be achieved under pressure
Performed in autoclave - similar to domestic pressure cooker, but better facilities for control
Organisms killed by combination of
- temperature
- hydration
- time

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21
Q

What are the three types of steam?

A
  • Superheated steam is water in the vapour phase and behaves like a gas. If the temperature decreases, the pressure decreases
  • Supersaturated steam or wet steam is in liquid phase and is made up of small droplets of water held in suspension by convection currents
  • Dry saturated steam exists on the phase boundary. If you lower the temperature it will condense
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22
Q

What the two types of heat?

A
  • Sensible heat: when exchanged, results in change of temperature
  • Latent heat: when exchanged, results in change of physical state - there is no temperature change
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23
Q

What are the two types of autoclaves?

A

Portable bench-top sterilisers
- design is similar to domestic pressure cooker

Large scale sterilisers
- gravity displacement autoclave
- porous load autoclave (vacuum-assisted)

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24
Q

What is air ballasting?

A

Sterile fluids may be packaged in flexible plastic containers (e.g. IV fluids)
Pressure in airspace above fluid may lead to bursting
to prevent this, some air may be retained to create overpressure in specifically designed autoclaves
To prevent layering of air, such autoclaves may require fan or spraying mechanism to mix air and steam

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25
Q

What are the three effects of air in the autoclave?

A
  1. Unjacketed bench autoclave
    Usually controlled by pressure only
    Air leads to lower temperature
  2. Jacketed autoclave
    Both pressure and temperature controlled
    Air can lead to superheating
  3. Layering
    Density of air = ~2 x density of steam
    Air forms layer in any container in upright position
    Air will be cooler
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26
Q

What are the 4 uses of dry heat sterilisation?

A

Substances that can’t be subjected to moisture
- Water soluble powders (thermostable)

Materials not penetrable by steam
- Oils, fats, waxes, dry items enclosed in sealed container etc.

Glassware
- Glass vessels, ampoules, syringes etc.

Metal surgical instruments
- Scalpels, forceps etc

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27
Q

What are the 4 disadvantages of dry heat sterilisation?

A
  • may take long time to heat up
  • temperature must be higher for longer than for moist heat sterilisation
  • some objects may oxidise at high temperature
  • large temperature variations can be found in a load
28
Q

What are the 2 advantages of gas sterilisation?

A
  • good alternative for materials that are sensitive to heat and/or radiation
  • some processes will even work at RT
29
Q

What are the 3 disadvantages of gas sterilisation?

A
  • slow - not suitable for high throughput sterilisation
  • toxic - requires more complex equipment, safe working protocols
  • gas may be absorbed - requiring addition of more gas during process
30
Q

What are the 3 advantages of using ethylene oxide for sterilising?

A
  • broad spectrum, non-selective
  • bactericidal
  • can act at room temp
31
Q

What are the 3 disadvantages of using ethylene oxide for sterilising?

A
  • expensive
  • difficult, potentially dangerous - toxic
  • need to store products after sterilisation in safe area while gas leaches out and disperses
32
Q

What are the 3 advantages of using formaldehyde for sterilising?

A
  • broad spectrum, non-selective
  • bactericidal
  • not flammable or explosive
33
Q

What are the 3 disadvantages of using formaldehyde for sterilising?

A
  • toxic
  • low penetration power; needs vacuum pulsing
  • slow acting
34
Q

What are the 4 types of radiation sterilisation?

A

Gamma rays
- most common method; requires radioactive source

Electron beams
- lower penetration power

X rays
- slower than electron-beam irradiation

UV light
- low penetration, only suitable for surface cleaning

35
Q

What are the three pyrogen tests?

A
  • Rabbit pyrogen test (RPT)
  • Limulus amoebocyte lysate (LAL) test
  • Monocyte Activation Tests (MAT)
36
Q

How do you calculate PSNU?

A

PNSU 1 in 10 (=10-1)
reducing probability to 0.1: IF = 102/10-1 = 103= 3 log cycles of kill

PNSU 1 in 106 (=10-6)
reducing probability to 10-6: IF = 102/10-6 = 108 = 8 log cycles of kill

37
Q

What is the F concept?

A

F-value: expresses lethality of heat treatment at any temperature equivalent to treatment at a reference temperature
F-value depends on resistance of reference organism; if using B. stearothermophilus (Z value is 10oC), and a process at 121oC, F value is denoted as F0
F-value is expressed in minutes

38
Q

What are the 4 ideal properties of disinfectants?

A
  • Broad spectrum
  • Rapid kill (5 mins)
  • Must not damage material to be disinfected
  • Easy to prepare and use
39
Q

What are the 4 ideal properties of antiseptics?

A
  • Adequate spectrum anti-microbial activity
  • Immediate and persistent activity
  • Cumulative (residual) activity
  • Non-toxic, non-irritant
40
Q

What are the 5 factors affecting choice of chemical agent?

A
  • Intended application
  • Number + type of micro-orgs present
  • Environmental factors
  • Safety, stability, cost, ease of use
  • Properties of chemical agent
41
Q

What are the 4 liquid disinfectantant evaluation test?

A

Suspension test: Calculates concentration of disinfectant/ antiseptic required to kill 99.999% of organisms

Time Kill:
Quantitative method particularly useful for antiseptics. (2 mins)

Minimum Inhibitory Concentration (MIC):
Semi Qualitative: MIC is lowest concentration showing no growth (overnight culture)

Disc test:
Qualitative indication of susceptibility to chemical agents (overnight growth)

42
Q

What are the 4 ideal properties of an excipient?

A

Cheap / inexpensive

Biologically inert – no physiological effects

Chemically inert – no reaction with API

Able to produce a range of physico-chemical properties – depending on application, e.g. viscosity and/or solubility

43
Q

What are the top 4 most common excipients?

A
  • Lactose
  • Microcrystalline cellulose
  • Cellulose ethers
  • Methylcelluloe
44
Q

What are the 5 advantages of aliphatic alcohol?

A
  • Broad antimicrobial activity
  • Rapid kill
  • Water soluble
  • Relatively non toxic
  • No residues
45
Q

What are the 5 disadvantages of aliphatic alcohol?

A
  • Not sporicidal
  • Some not virucidal
  • Poor penetration of organic matter
  • High dilution coefficient (used at >50%)
  • Flammable
46
Q

What are the 4 advantages of aldehydes?

A
  • Broad spectrum
  • Sporicidal
  • Rapid kill
  • Not affected by organic matter
47
Q

What are the 2 disadvantages of aldehydes?

A
  • Unstable
  • Toxic
48
Q

What are the 2 advantages of biguanides?

A
  • Good bactericidal activity
  • Non toxic
49
Q

What are the 4 disadvantages of biguanides?

A
  • Not active against mycobacteria or viruses
  • Not sporicidal
  • Not v. soluble in water
  • Activity ↓ by anionic compounds
50
Q

What are the 4 advantages of Hypochlorites?

A
  • Readily available
  • Cheap, Compatible
  • Broad spectrum
  • Rapid kill
51
Q

What are the 4 disadvantages of Hypochlorites?

A
  • Corrosive
  • Irritant
  • Inactivated by organic matter
  • Unstable
52
Q

What are the 3 advantages of Iodine?

A
  • Broad spectrum
  • Rapid kill
  • Less affected by pH, temp & organic matter than Cl2 based compounds
53
Q

What are the 2 disadvantages of Iodine?

A
  • stains skin & fabric
  • irritant
54
Q

What are the 2 advantages of Peroxygen compounds?

A
  • Powerful antimicrobials & sporicides
  • Active in presence of organic matter
55
Q

What are the 3 disadvantages of Peroxygen compounds?

A
  • Unstable in sunlight
  • Irritant
  • Corrosive
56
Q

What are the 2 advantages of phenolics?

A
  • Good antimicrobial activity; poor sporicide
  • Cheap
57
Q

What are the 3 disadvantages of phenolics?

A
  • some harmful / toxic
  • some have strong odour
  • some corrosive
58
Q

What are the 4 advantages of substituted phenols?

A
  • Broad spectrum
  • Rapid kill
  • Cheap
  • Not affected by organic matter
59
Q

What are the 2 disadvantages of substituted phenols?

A
  • Not sporicidal
  • Leave residues
60
Q

What are the 5 advantages of Cationic surface-active agents: QACs?

A
  • Water soluble
  • Non toxic
  • Non corrosive
  • Broad spectrum
  • Active at low conc
61
Q

What are the 2 disadvantages of Cationic surface-active agents: QACs?

A

Not sporicidal
Activity decr. by organic matter

62
Q

What are the 3 requirements for antimicrobial activity?

A
  • Adsorption to cell surface (requires moisture - must be wet, all disinfectants have a ‘wet time’ or contact time)
  • Passage into cell (structure of outer surface effects sensitivity to disinfectants)
  • Interaction with target (once inside cell disinfectants have a specific target (eg ribosme/ nucleoid etc)
63
Q

What is the mode of action of oxidation as resistance?

A

Strand breakage, binding to DNA or RNA-
Disruption of transcription, translation and replication

Reaction and degradation of unsaturated fatty acids in cell membranes
(disrupts membrane and ultimately leads to leakage of cytoplasmic contents)

Modification of bonds in proteins = loss of structure
Disrupts enzyme function = in cell death

64
Q

What is the mode of action of coagulation and x-linking as resistance?

A

Coagulation
Macromolecule denaturation– leads to extensive coagulation and precipitation, (disruption of cytoplasm, lipid membranes etc)

X-linking
Aldhehydes cause the cross linking of lysine residues to other amino acids- changes protein structure and causes protein aggregation.

65
Q

What is the mode of action of disruption as resistance?

A

Disruption of functional structures ( cell wall/ cytoplasmic membrane)
- Positively charged ions have affinity for negatively charged microbial membranes
- This affinity causes disruption of the proton motive force
- Disrupts cell membrane-associated activities eg energy generation

66
Q

What is acquired phenotypic resistance?

A
  • intracellular bacteria
  • biofilms
67
Q

What is acquired genetic resistance?

A
  • chromosomal mutation / gene transfer
  • efflux
  • MDR plasmids