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BI302 > R.O Lecture 5&6 > Flashcards

R.O Lecture 5&6 Flashcards

1
Q

What is the rate of microbial death affected by?

A

*Microbial characteristics/susceptibilities
*Environmental influences such as:
- 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

A

Reduction in the number of pathogenic microogranisms 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 destry 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

What are the ideal 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

Mechanisms of Action - Effects on Protein

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

Denaturation of Protein (Bacteriocidal)

A

Active Protein - Inactive Protein - No reconfiguration; permanentely denatured

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10
Q

Denaturation of Protein - Bacteriostatic

A

Active Protein - Inactive Protein - Reconfiguration, temporarily denatured

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11
Q

Mechanisms of Action - Effects on Membranes

A
  • Denaturationof Protein Component
  • Disruption of Lipids
    - Surfactants (Alcohols, detergents, quats)
    - Wetting agents
    - Indirect effect
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12
Q

Mechanisms of Action for Nucleic Acids

A

Nucleic Acids: Damage from heat, radiation, chemicals

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13
Q

Mechanisms of Action for Energy-producing systems

A

E.g. Fermentation inhibition by lactic acid or propionic acid

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14
Q

Mechanism of Action - Cell Walls

A

Dyes (e.g. crystal violet) can interfere with cell wall formation

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15
Q

Control Methods can be…?

A

Chemical or Physical

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16
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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17
Q

Chemical Antimicrobial Agents - Phenols

Phenol and phenol derivatives (phenolics):

A
  • 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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18
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 material
  • Iodophors (Iodine combined with organic molecule): slow release, less irritating , surgical scrubs and skin antiseptic
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19
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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20
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
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21
Q

Chemical AntiMicrobial Control - Oxidising Agents

A
  • Disrupt disulfide bonds - hydrogen peroxide is used to clean puncture wounds, potassium permangenate to disinfect instruments.
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22
Q

Chemical Antimicrobial Agents - Alkalating Agents

A

Disrupt structure of proteins and nucleic acids.
Fomehaldehyde is used to inactivate viruses without destroying antigenic properties, glutaraldehyde to sterilize equipmentn

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23
Q

Chemical Microbial Agents - Dyes

A
  • May interfere with replicatoin or block cell wall syntheisis
  • Acridine is used to clean wounds, crystal violet to treat some protozoan and fungal infections.
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24
Q

Name the Physical Agents used as control methods

A
  • Heat (Various Methods)
  • Refrigeration
  • Desiccation
  • Irradiation
  • Filtration
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25
Q

Heat

A
  • Cheapest, most effective and widely used control
  • Denatures enzymes
  • Suitable for materials undamaged by heat
  • Various approaches:
  • Dry heat
  • Moist heat
  • Pasteurisation
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26
Q

Dry Heat

A
  • Used to sterilise metal objects and glassware
  • Flame: Innoculating loops, flasks/tube mouths
  • Dry heat sterilisation for moisture-sensitive materials
  • Longer heating times/temperatues than moist heat
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27
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
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28
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

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29
Q

Physical Agents - Lower temperatures

A
  • Refrigeration: (2-8 degrees) Slows growth based on reduction in enzyme kinetics
  • Freezing : (-20 degrees) slows metabolic activity to prevent food spoilage but does not kill organisms.
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30
Q

Physical Agents - Dessication

A
  • Water absence inhibits enzymatic activity
  • Usually bacteriostatic, but may be bactericidal depending
    on the species
  • Used to preserve some foods
  • Freeze-drying: Lyphilisation - used to preserve bacterial cultures.
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31
Q

Physical Agents - Radiation. Name the 3 main types

A
  • Ultraviolet (UV) light
  • Ionising Radiation
  • Microwave Radiation
32
Q

Ultraviolet (UV) light

A

Ultraviolet (UV) light: (40 – 390 nm) Works best at 200nm;
Used for sterilising surfaces
Damages DNA and proteins; DNA repair can aid survival

33
Q

Ionising Radiation

A

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.

34
Q

Microwave Radiation

A

(1mm – 1m) Acts on water molecules which release
heat – not effective on spores

35
Q

Physical Agent - Filtration

A
  • Passage of liquid/gas through small pores; traps in a sizespecific 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
36
Q

What pore sizes of membrane filters are used most often?

A
  • 0.45 - a few bacteria, viruses molecules
  • 0.22 - viruses, molecules
  • 0.10 - medium-sizes to small viruses molecules
37
Q

Physical Agent - Osmotic Pressure

A

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

38
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.
39
Q

Physical Antimicrobial Agent - Strong Physical Light

A
  • Oxidation of light-sensitive materials - can be used with dyes to destroy bacteria and viruses: may help sanitize clothing.
40
Q

What are the methods for evaluating a disinfectant?

A
  • Phenol coefficient
  • Filter Paper Method
  • Use-dilution Test
41
Q

How do we decide whethere a disinfectant is effective?

A

Agents that prevent growth at the lowest concentrations
are considered the most effective disinfectants

42
Q

Phenol coefficient

A
  • Comparison to the ‘original’ disinfectant
  • Some disadvantages
43
Q

Use-dilution tests

A
  • Test bacteria coated onto carrier rings
  • Incubated in test solutions (time based on product)
  • Cultured in broth to detect surviving microbes
44
Q

Filter Paper Method

A

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

45
Q

Name the methods for Measuring sensitivity to an antimicrobial agent.

(antibiotic susceptibility testing)

A
  • Disc-diffusion (Kirby-Baeur) method
  • E (epilsometer test)
  • Dilution Method
46
Q

Disc-diffusion (Kirbay-Bauer) method

(antibiotic susceptibility testing)

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
47
Q

E (epsilometer test)

antibiotic susceptibility testing

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
48
Q

The dilution method

(antibiotic susceptibilty testing)

A
  • Bacteria inoculated into serial dilutions of an antimicrobial agent
    MIC can be determined
  • Measuring sensitivity to an antimicrobial agent
    (antibiotic susceptibility testing)
  • Can combine with second test to determine if bacteriostatic or
    bacteriocidal (minimum bactericidal concentration; MBC)
49
Q

Antimicrobial agent/drug

A

Chemical substance used to treat diseases cause by pathogenic mcrobes

50
Q

Antibiotic

A

Chemical substance (drug) produced by microogransims, with the capacity to control growth/kill microbes.

Bacteriostatic or bacteriocidal
Synthetic or natural product (bacteria/fungi)

51
Q

Who discovered antibiotics? Exaplain the discovery.

A
  • Alexander Fleming (1929)
  • Penicillium notatum inhibited S.aureus
  • Recognised growth inhibition potential - Penicillin
  • Mass production by 1940s (WW2)
  • Post-war studies led to discovery of new antibiotics
52
Q

Properties of useful chemoterapeutic agents

A
  • Selectively toxic to pathogens; non-toxic to host and minimal effect on normal microbial flora – determine chemotherapeutic index
  • Should not stimulate an allergic reaction (hypersensitivity)
  • Host should not destroy or neutralise drug before effective
  • Pathogens should not easily become resistant to the drug
  • Agent should reach the site of infection (solubility)
53
Q

Chemotherapeutic index

A

Chemotherapeutic index. The ratio of the minimal effective dose of a chemotherapeutic agent to the maximal tolerated dose.

54
Q

Spectrum of activity

Look at slide 22

A

Range of different microogranisms treatable with an agent

55
Q

Broad Spectrum

Antimicrobial Agents

A

Broad spectrum: Active across a wide range of taxonomic
groups; useful for untargeted treatment without pathogen
identification

56
Q

Narrow Spectrum

Antimicrobial Agents

A
  • Narrow spectrum: Specifically targets small number of
    organisms; may protect host microflora; reduces development
    of drug resistance
57
Q

Name the 5 major modes of action of common antimicrobial agents

A
  1. Inhibition of Cell Wall Synthesis
  2. Disruption of Cell Membrane Function
  3. Inhibition of Protein Synthesis
  4. Inhibition of Nucleic Acid Syntheisis
  5. Action as Antimetabolites
58
Q

Name the antibiotics used for the Inhibition of cell Wall Synthesis

A
  • Penicillins
  • Cephalosporins
  • Bacitracin
  • Vancomycin
59
Q

Penicllins - Inhibition of Cell Wall Syntheisis

Mechanisms of antimicrobial agent activity

A
  • Penicillins: Bactericidal; All contain a β-lactam ring;
  • Natural penicillins (G, V) are penicillinase sensitive and
    narrow spectrum.
  • Semi-synthetic penicillins are modified to increase penicillinase resistance and broaden spectrum (e.g.methicillin, ampicillin, amoxicillin)
  • Interfere with PG cross-linking: Targets PBP
60
Q

Cephalosporins - Inhibition of cell wall synthesis

Mechanims of Antimicrobial Agent Activity

A
  • Cephalosporins - effective against Gram-negatices
  • Resistant to Penicilliniases
  • More expensive; mainly IV/IM
  • Interfere with PG cross-linking Targets PBP
61
Q

Bacitracin- Inhibition of cell wall syntheis

Mechanisms of Antimicrobial Agent Activity

A
  • Bacitracin: Polypeptide antibiotic
  • Effective against Gram positives
  • Topical application
  • Interfere with linear PG strand formation
62
Q

Vancomycin

A
  • Vancomycin: Glycopeptide antibiotics;
  • Narrow spectrum;
  • toxic
  • Penicillinase-resistant
  • Interfere with linear PG strand formation
63
Q

Penicillin and Cephalosporin both bind to target enzymes (PBP) via B-lactam ring. Penicillin has 1 R site, Cephalosporin has 2. Why is this significant?

PBP- transpeptidase

A
  • Peniclllin has one R site, which means it can only bind to one target in bacteria. This limits its spectrum of activity and makes it more effective against certain types of bacteria than others.
  • Cephalosporsins, have two R sites, which gives them a broader spectrum of actiity and makes them more effecive against a wider range of bacteria than penicllin. These two R sites also make cephalosprins more resistant to certai bacterial enzymes than can break down penicllin.

look at slide 25 for the common method of administration of each.

64
Q

Describe how the disruption of cell membrane Functions.

Mechanism of antimicrobial agent activity

A

Alter permeability of bacterial cell membranes; Polypeptide
antibiotics; clinical application limited to certain members due to
similarities between host and bacterial cell membranes

65
Q

Polymyxins - Disruption of cell membrane function

A
  • Polymyxins: (A, B, C, D, E) used only when pathogen is
    resistant to other less toxic antibiotics; Gram negatives; Topical
66
Q

Nystatin - disruption of cell membrane function

A

combine with sterols; therefore effective against
mycoplasmas (and also systemic fungal infections).

67
Q

Colicins - disruption of cell membrane function

A
  • Bacteriocin of E.coli; encoded by Col plasmid, which
    also codes for immunity protein.
  • Kills bacterial cells not carrying the plasmid e.g. cells of same species.
68
Q

Bacteriocin

A
  • Similar to antibiotics
  • Produced only by bacteria
  • Specific to certain bacterial strains , wheras antibiotics can be effective against a broad range of bacteria.
69
Q

Inhibition of Protein SYntheisis

A

Takes advantage of differences between bacterial and eukaryotic ribosome - selective toxicity

70
Q

Aminoglycosides - inhibition of protein syntheisis

A
  • Amino sugars linked by glycoside bonds. Broad
    spectrum.
  • Bacteriocidal; bacteriostatic at lower doses. Work
    synergistically with other compounds (e.g. penicillin)
  • Streptomycin (1940s); now has high resistance levels; toxic.
  • Other compounds (kanamycin, gentamicin etc.)
71
Q

Tetracylines - inibition of protein syntheisis

A

Tetracyclines: Interfere with tRNA attachment. Bacteriostatic; very
broad spectrum; can inhibit intestinal microflora

72
Q

Chloramphenicol - Inhibition of Protein Synthesis

A

Bacteriostatic; broad spectrum ; inhibits peptide bond formation. Damages bone marrow.

73
Q

Macrolides - Inhibition of protein syntheisis

A

Macrolides: Erythromycin – Bacteriostatic. Can not penetrate
Gram negative cell walls. Used as an alternative to Penicillin

74
Q

Inhibition of nucleic acid syntheisis

A

Can be Toxic to host cells due to common targets.
* Rifampin: Inhibits mRNA synthesis by binding RNA polymerase;
High absorbance into tissues and cells; Bactericidal; Broad
Spectrum; Interacts with other drugs; Treatment of mycobacteria
infections-leprosy and tuberculosis
* Quinolones: Blocks bacterial enzyme that unwinds DNA prior to
replication; Broad spectrum; Used for UTIs; Can affect cartilage
development

75
Q

Actions as Antimetabolites

A

Compounds that interfere with metabolic reactions by:
1) Competitive inhibition of enzymes or
2) Erroneous incorporation into important molecules

BI302 (11 decks)

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