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BI302 Microbiology > Bacteriology lecture 5 > Flashcards

Bacteriology lecture 5 Flashcards

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1
Q

what is the rate of microbial death is affected by?

A
  • Microbial characteristics/susceptibilities
  • Environmental influences
  • Number of Microbes (Proportional death rates)
  • Time required for sterilisation
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2
Q

Sterilisation

A

The killing or removal of all microorganisms in a material or object

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3
Q

Disinfection:
Bactericide: Agent that kills bacteria (though not spores)

A

Reduction in the number of pathogenic microorganisms on surfaces/objects to the point where they pose no danger of disease

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4
Q

Antiseptic

A

Chemical agent that is safe to use externally on living tissue to destroy microbes or inhibit their growth

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5
Q

Bacteriostatic agent

A

An agent that inhibits the growth of bacteria

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6
Q

Bactericide

A

Agent that kills bacteria (though not spores)

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7
Q

I deal qualities for selecting a disinfectant

A
  • Fast-acting
  • Non-toxic
  • Non-damaging to material
  • Wide spectrum
  • Easy to prepare/stable
  • Inexpensive
  • Odour
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8
Q

Effects on Proteins

A

Denaturation of Protein:
- Permanent/Temporary
- hydrolysis by acids/alkalis
- oxidation by H2O2, KMnO4, halogens
- alkylating agents (e.g. some dyes) etc.

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9
Q

Effects on Membranes

A
  • Denaturation of Protein Component
  • Disruption of Lipids:
  • Surfactants (Alcohols, detergents, quats)
  • Wetting agents
  • Indirect effect
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10
Q

Effects on Other Cell Components

A
  • Nucleic Acids: Damage from heat, radiation, chemicals
  • Energy-producing systems: E.g. Fermentation inhibition
    by lactic acid or propionic acid
  • Cell walls: Dyes (e.g. crystal violet) can interfere with cell wall formation
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11
Q

Control methods can be

A
  1. Chemical
  2. Physical (e.g. heat or irradiation)
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12
Q

Chemical Antimicrobial Agents:
Soaps and Detergents

A

Remove microbes, oily substances and dirt
- Anionic: Clothes laundering, household cleaning agents (less effective)
- Cationic: Sanitize food utensils (kill some viruses)
- Quaternary ammonium compounds (quats)
- Mixtures can increase efficacy

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13
Q

Chemical Antimicrobial Agents: Phenols

A

Phenol and phenol derivatives (phenolics):
-Denature proteins/enzymes and disrupt membranes
-Action not impaired by organic material
-Halogen addition can increase effectiveness
-E.g. Amphyl and Lysol: retain properties for days, safe on skin and medical instruments

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14
Q

Chemical Antimicrobial Agents
Halogens

A
  • Particularly Iodine and Chlorine; alone (I2 or Cl2) or part of compounds (NaOCl)
  • Agent used in drinking water and swimming pools (HClO)
  • Can be inactivated by organic materials
  • Iodophors (Iodine combined with organic molecule): Slow-release, less irritating, surgical scrubs and skin antiseptic
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15
Q

Chemical Antimicrobial Agents:
Alcohols

A
  • Denature protein when mixed with water
  • Dissolve lipids (cell membranes)
  • Effective against bacteria & fungi, but not endospores/ unenveloped viruses
  • Evaporates quickly (low exposure time)
  • Used as skin antiseptic (isopropanol or ethanol; effective at 60-95% (v/v)
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16
Q

Chemical Antimicrobial Agents:
Heavy Metals and their compounds

A
  • Selenium, Mercury, Copper, and Silver
  • Very effective in small quantities (oligodynamic action) - Selenium sulphide: Kills fungi; Anti-dandruff shampoo
  • Silver wound dressings; Calamine lotion
17
Q

Many Physical Agents used for food preservation and preparation Includes:

A
  • Heat (Various Methods)
  • Refrigeration
  • Desiccation
  • Irradiation
  • Filtration
18
Q

Physical Agents: Heat

A
  • Cheapest, most effective and widely used control
  • Denatures enzymes
  • Suitable for materials undamaged by heat
  • Various approaches:
  • Dryheat
  • Moistheat
  • Pasteurisation
19
Q

Dry heat

A
  • Used to sterilise metal objects and glassware
  • Flame: Innoculating loops, flasks/tube mouths
  • Dry heat sterilisation for moisture-sensitive materials:
    1) 170 °C for 1 h
    2) 160 °C for 2 h
    3) 121°Cfor16h
20
Q

Moist heat

A
  • Causes denaturation of proteins and may disrupt membrane lipids-widely used
  • Boiling water can kill most vegetative bacteria and fungi
    Heating water under pressure (higher temps) in an autoclave: 121 °C for 15-20 min can kill also spores
21
Q

Moist heat

A
  • Causes denaturation of proteins and may disrupt membrane lipids-widely used
  • Boiling water can kill most vegetative bacteria and fungi
    Heating water under pressure (higher temps) in an autoclave: 121 °C for 15-20 min can kill also spores
22
Q

Pasteurisation

A
  • Invented by Pasteur; does not achieve sterility
  • Kills pathogenic organisms in raw products (milk etc)
  • Flash method: 71.6 °C for 15 sec
  • Holding method: 62.9 °C for 30 min
  • Ultrahigh temperature processing (UHT): 74°C140°C 74°C (5 sec) Can be stored at RT
23
Q

Lower temperatures

A
  • Refrigeration: (2 – 8 °C) Slows growth based on reduction in enzyme kinetics
  • Freezing: (-20 °C) Slows metabolic activity to prevent food spoilage but does not kill organisms
24
Q

Dessication

A
  • Water absence inhibits enzymatic activity
  • Usually bacteriostatic, but may be bactericidal depending on the species
  • Used to preserve some foods
  • Freeze-drying: (Lyophilisation)
  • Freeze-dried coffee
  • Used to preserve bacterial cultures
25
Q

Radiation

A
  • Ultraviolet (UV) light: (40 – 390 nm) Works best at 200nm; Used for sterilising surfaces
  • Damages DNA and proteins; DNA repair can aid survival
  • Ionising Radiation: X-rays and gamma rays (< 40 nm) – dislodge electrons from atoms, creating ions and radicals.
  • Radicals kill by interacting with DNA, proteins, lipids etc.
  • Microwave Radiation: (1mm – 1m) Acts on water molecules which release heat – not effective on spores
26
Q

Filtration

A
  • Passage of liquid/gas through small pores; traps in a size- specific manner
  • Membrane filters: Specified pore sizes (0.025 – 25 μm)
  • Suitable for heat-sensitive materials (e.g. media supplements, drugs, vitamins)
  • HEPA (High-efficiency particulate air) filters in labs
27
Q

Osmotic Pressure

A
  • High salt/sugar concentrations draw water from cells
  • Bacteriostatic: metabolism cannot progress
  • Food preservation: Curing, pickling, jams etc.
28
Q

Sound

A
  • Ultrasonic waves can cause bacteria to cavitate – denatures proteins and disintegrates bacteria
  • Can be used to lyse bacteria to release components for study, but not practical for sterilisation
29
Q

Sound

A
  • Ultrasonic waves can cause bacteria to cavitate – denatures proteins and disintegrates bacteria
  • Can be used to lyse bacteria to release components for study, but not practical for sterilisation
30
Q

what is used when
Evaluating A Disinfectant?

A
  • Phenol coefficient:
  • Filter Paper Method:
  • Use-Dilution Test:
    Agents that prevent growth at the lowest concentrations are considered the most effective disinfectants
31
Q

Phenol coefficient

A
  • Comparison to the ‘original’ disinfectant
  • Some Disadvantages
32
Q

Use-dilution Tests steps

A
  1. Test bacteria coated onto
    carrier rings
  2. Incubated in test solutions (time based on product)
  3. Cultured in broth to detect surviving microbes
33
Q

Filter Paper Method

A

Efficacy of a Chemical Agent applied to a filter paper disc In vitro results may not translate in practice

34
Q

What methods are used in
Measuring sensitivity to an antimicrobial agent?

A
  • Disc-diffusion (Kirby-Bauer) method
  • E (epsilometer) test
  • The dilution method
35
Q

Disc-diffusion (Kirby-Bauer) method

A
  • Lawn of target bacteria spread over plate
  • Specific concentrations of antimicrobial agents on filter paper discs
  • Zones of inhibition measured (diameter)
  • Issues due to bacteriostatic vs. bactericidal actions
36
Q

E (epsilometer) test

A

E (epsilometer) test determines sensitivity to antibiotic and also minimum inhibitory concentrations (MIC) – antimicrobial gradient

Gradient of antibiotic concentrations on a strip (high to low)

Intersection of zone of inhibition with the strip used to determine the MIC

37
Q

The dilution method

A
  • Bacteria inoculated into serial dilutions of an antimicrobial agent
  • MIC can be determined
  • Can combine with second test to determine if bacteriostatic or bacteriocidal (minimum bactericidal concentration; MBC)

BI302 Microbiology (2 decks)

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