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Microbiology PMY 3 > Microbial Growth Control-week 7 > Flashcards

Microbial Growth Control-week 7 Flashcards

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1
Q

What are the basic principles of control?

A
  1. Microorganisms have specific environmental requirements
  2. Certain structures and/or processes are essential
  3. Any control strategy has to be tailored
    • What(is the object being treated)
    • How many (microorganisms are present)
    • What types/species are present
    • What is the end goal?
  4. Not all control methods are equally effective
  5. Not all microorganisms are equally susceptible
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2
Q

What are the 5 examples of antiseptic agents?

A

Alcohol

Iodophors

Chlorexidine

Parachlorometaxylenol

Triclosan

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3
Q

What microorganisms are susceptible to alcohol

?

A

Bacteria, myobacteria, fungi and viruses

Bacterial spores are not susceptible to alcohol

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4
Q

Describe heat as a common treatment for controlling microbial growth

A

Moist heat:

  • boiling
  • Autoclaving

Dry heat
-ovens

Incineration

Uses includes

Glassware
Lab media
Surgical instruments

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5
Q

Why does heat act as a medium for controlling microbial growth?

A

Coagulates proteins: hydrogen bonds are broken

Native protein becomes coagulated proteins

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6
Q

What is an autoclave?

A

A variation of a pressure cooker

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7
Q

What is the correlation between steam and temperature ?

A

Steam is put under pressure, to result in higher temperature

Steam @ 1 atm(normal pressure)=100 degrees celsius

Steam @ 2atm(+15 psi)= 121 degrees Celsius

This temperature for 15 minutes kills most microorganisms and their spores

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8
Q

What are the advantages of using autoclave/steam/ pressure to kill microorganisms?

A
  • Can be used on a range of items
  • Effective; inexpensive
  • Damages a wide range of microorganisms
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9
Q

What types of radiation are used to control microbial growth?

A

Non-ionizing radiation: Ultraviolet(UV)

Ionizing: gamma or X-ray

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10
Q

What is used on objects that cannot be autoclave?

A

Radiation

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11
Q

What objects use radiation when controlling microbial growth?

A
  • Heat sensitive plastics e.g., gloves, Petri dishes
  • Food items, including spices
  • Biological hoods/cabinets, surgical rooms
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12
Q

Contrast the wavelengths of ionizing and non-ionizing

A

Non-ionizing: gamma and x-rays have 0.1-40 nm wavelength

Ionizing: UV range= 50-400nmwavelength

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13
Q

Contrast ionizing and non-ionizing radiation in terms of chemical abilities and effect on DNA

A

Ionizing:
-Dislodges electrons from atoms

-Damages DNA and produces peroxides

Non-ionizing:

Absorbed by purines and pyrimidine bases and forms pyramiding dimers

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14
Q

Contrast ionizing and non-ionizing in terms of penetration abilities

A

Ionizing : penetrates well

Nom-ionizing: doesn’t penetrate well: limited to surface sterilization

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15
Q

When liquids cannot be autoclaved or radiated, how can microbial growth be controlled?

A

Filtration

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16
Q

How can filtration be done to to control microbial growth?

A

Physical separation using a filter, with pores that block the microorganism

E.g. 0.25 micron filter: 1-2 micron bacteria are too large to pass through the holes of the filter

-Mainly for sterilization of small volumes of liquids that are heat-sensitive

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17
Q

What are the basic principles of chemical control?

A

-Apply a chemical as a spray, solution, mist, etc.

  • Certain chemicals can inhibit/halt, kill or lyse microorganisms
    - effect can vary depending on:
    • microorganism
    • type of compound
    • concentration of the compound
  • Some chemical control agents have very general mechanism of action
    • e.g. damage cell membranes
      - might also be toxic to human cells
  • Some are very specific
    • e.g. target unique structures or processes
    • less likely to be toxic to human cells
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18
Q

How may a compound affect the growth of a microbe ?

A

Reactions include hydrolysis, oxidation, alkylation etc.

A. Reactions affecting proteins

B. Reactions affecting membranes

C. Reactions affecting cell components

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19
Q

What is the mechanism of alcohol as a chemical control agent?

A

Lipid solvent and protein denaturant

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20
Q

What is the mechanism of action of Hydrogen peroxide (3% solution) as an antiseptic)?

A

Oxidizing agent

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21
Q

What is the mechanism of action of iodophors as a chemical control agent?

A

Iodinated proteins

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22
Q

What is the mechanism of action of chlorine compounds(e.g. sodium hypochlorite [bleach] )?

A

Oxidizing agent

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23
Q

What is the mechanism of action of ethylene oxide gas as a chemical control agent?

A

Alkylating agent

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24
Q

What is the mechanism of action of pine oils (e.g. pine-sol) as a chemical control agent?

A

Protein denaturant

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25
Q

What are the possible outcomes of antimicrobial growth that can be due to antimicrobial agents?

A

Static- total cell count and viable cell count plateau.

Cidal- total cell count plateaus while viable cell count decreases

Lytic- both total cell count and viable cell count decrease

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26
Q

What are the features of sterilants, disinfectants and sanitizers used?

A

Non-living surfaces
E.g. sodium hypochlorite[bleach], gluteraldehyde, ozone
-inhibit or kill microorganisms present on inert surfaces

-Nonspecific mechanisms
    Damage cell membranes
    Denature proteins
    Inactivate enzymes
-Not usually suitable for use on living tissues

-can be combined with e.g. a surfactant(for better cleaning

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27
Q

What are applications of antiseptics?

A
  1. Reduce numbers of microorganisms from mucous membranes before surgery e.g. iodine
  2. Remove microorganisms from skin before an injection
    E.g. alcohol
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28
Q

What are therapeutic or “in Vivo”antimicrobials?

A

Natural or synthetic compounds with activity against microorganisms, that can be used therapeutically to treat infection

  • some can be used as creams, powders or lotions others are given orally or by injection
  • Tend to have more specific targets(such as a specific enzyme) compared to chemical control agents that might target e.g., membranes
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29
Q

How are antimicrobials classified?

A

A. Molecular structure

B. Mechanism of action, e.g. -protein synthesis inhibitors

C. Spectrum(range) of activity

D.2 basic categories of antimicrobials:

  1. Synthetic antimicrobial drugs
  2. Naturally occurring antimicrobial drugs “antbiotics”
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30
Q

Give some examples of molecular structures of therapeutic antimicrobials

A

Tetracyclines e.g. tetracycline protein inhibitors

Glycopeptides e.g. Vancomycin

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31
Q

Describe how main targets/ mechanism of action may differ among therapeutical antimicrobials

A
  1. Protein synthesis- 30s tetracyclines, 50s chloramphenicol
  2. Cell wall synthesis- B lactams
  3. Cell membrane function- Polymyxins
  4. metabolism- trimethoprim
  5. Nucleic acid synthesis- sulfonamides
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32
Q

What is selective toxicity?

A

Requirement for targeted effect on the microorganism, with minimal damage to host cells

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33
Q

Of all the drugs, only a fraction are clinically useful, why?

A

Side effects: toxic or harmful

-cellular damage to host

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34
Q

Describe synthetic antimicrobials

A

E.g, chemical dyes, manufactured compounds

Started with the work of Ehrlich and Domagk

Based around the idea of growth factor analogs:

  • structurally like a growth factor, e.g. a purine
  • But: subtle differences stop the microorganism from using it properly

E.g. sulfonamides, quinolone

35
Q

Describe antibiotics

A

.g. Naturally produced by soil fungi, other bacteria

Can be subsequently modified, e.g. to make them acid-stable (can be swallowed) or extend the range of bacteria they work against

Various microbial targets, including:
I. Interfering with protein synthesis

II. Interfering with bacterial cell wall synthesis

36
Q

What is a basic mechanism of antibiotics?

A

Basic mechanism: inhibit translation by interacting with ribosome

Examples of antibiotics in this category:

Amino glycosides-target 30S subunit: e.g., streptomycin-

Macrolides - target 50s subunit e.g. azithromycin

Tetracyclines-target 30s subunit e.g. tetracycline

37
Q

Describe the antibiotics that interfere with peptidoglycan synthesis

A

The antibiotics are structurally similar (“analogs”) to D-ala-D-ala

  • bind to and Schlage the transpeptidase enzyme
  • Can’t function —> no cross-linking
  • examples of antibiotics with this mechanism includes the B-lactate antobiotics
    • penicillins group (e.g. Amoxicillin, Penicillin G)
    • Cephalosporins
38
Q

Do therapeutic medicine categories work for other compounds they are designated for?

A

Antibiotics don’t work against fungi, antifungals don’t work against viruses etc.

With one or two exceptions

39
Q

What are the basic principle common with all therapeutic compounds?

A

Interfere with a fundamental process or structure

40
Q

What structures are affected by antifungals?

A

Fungal cell wall, cytoplasmic membrane

41
Q

Why are there much less antivirals than antibiotics?

A

Treating viral infections requires compounds that have different targets relative to antibiotics

42
Q

What is the rationale of inhibitors of reverse transcriptase?

A

Due to genetic variation material of virus, replication of nucleic acid requires the virus to encode for a specialized enzyme

43
Q

Some antivirals inhibit reverse transcriptase, why is this a good strategy?

A

Reverse transcriptase is UNIQUE to certain viruses (e.g. HIV, HBV); no equivalent exists in the eukaryotic cells

44
Q

What is the mechanism of inhibiting reverse trsnscriptase?

A

Nucleoside analog*

  • Activated (phosphorylated) inside the infected cell
  • Inhibit the viral polymerase (reverse transcriptase)
45
Q

Give examples of antivirals which inhibit reverse transcriptase

A

Zidovudine(AZT)

Stavudine

46
Q

What is the general challenge with viruses?

A

How to target the virus without (negatively) impacting the host cell that it is replicating in, using the enzymes of, etc.

Inhibiting reverse transcriptase is a common mechanism in antivirals. But other polymerases can be affected

47
Q

What is the outline of inhibiting viral enzymes and RNA polymerase?

A
  1. Acyclovir (acycloguanosine)converted by a viral thymidine kinase
  2. This creates ACV-monophosphate which is converted to cellular thymidine kinases
  3. This creates ACV-diphosphate
  4. ACV-triphosphate then inhibits viral DNA polymerase
48
Q

What is the mechanism usually used by antifungals?

A

Inhibitors of Ergosterol

49
Q

What is the rationale of antifungals inhibiting ergosterol?

A

By impacting ergosterol, the fungal cell membrane is weakened and doesn’t function properly

50
Q

Why is inhibiting ergosterol for antivirals, a good idea?

A

Ergosterol is UNIQUE to fungi; not present in mammalian membranes

51
Q

Give an example of inhibiting ergosterol for antifungals

A

A) bind to ergosterol and cause formation of pores —> leakage of cell contents and cell death

B) interfere with pathway for ergosterol formation —> weakened fungal formation

52
Q

Give examples of antifungals that inhibit ergosterol

A
  1. Bind directly to ergosterol: polyenes

2. Inhibit fungal enzyme used in ergosterol synthesis: azoles

53
Q

Outline how antifungals bind directly to ergosterol to inhibit it

A
  1. Bind directly to ergosterol such as polyenes e.g. Amphotercin B

Antifungals that do this: polyenes e.g. amphotercin b

  • normal role of fungal sterols = maintain structure and function of membrane
  • binding of antifungal to sterols —>
  • channel function
  • leakage of f cytoplasmic contents

-death of the fungus

54
Q

Outline how antifungals may inhibit ergosterol synthesis pathway

A

Antifungals such as Azoles e.g. fluconazole

  • Target the enzyme that converts lanosterol into ergosterol
  • Lanosterol builds up in fungal cell
  • Cell membrane isn’t properly permeable
  • Cell contents leak out
    • fungi are killed
55
Q

Why is microbial resistance/or lack of susceptibility a problem?

A

Drugs no longer work:
-higher, more toxic concentrations needed

  • switch to a more expensive treatment
  • longer period for treatment
  • side effects
  • most genes encoding for resistance are carried on mobile genetic elements such as plasmids and transposons
    - enables rapid spread

-Single gene (1 antibiotic), or multiple —> resistance to many different antibiotics, or entire families(e.g., resistance to all B-lactate antibiotics)

56
Q

What is resistance?

A

Normal therapeutic methods are no longer working

57
Q

How can resistant bacteria increase in number due to antibiotics?

A

Resistant bacteria cannot be killed

Resistant bacteria multiply

Resistant genes are often encoded on transmissible genetic elements such as plasmids

58
Q

How bacteria evade antibiotics?

A

-Prevent accumulation -decrease/block uptake
E.g. Multi-drug resistance pumps

  • Change target site-Change in receptor site affinity, modification of target pathway
  • Produce an inactivating enzyme- e.g. B-lactamases

Chloramphenicol acetyltransferases

59
Q

Describe cross linkage in gram positive bacteria and the enzyme responsible

A

Cross linking of the peptidoglycan layers requires removal of terminal D-ala

Done by an enzyme: Transpeptidase/ penicillin- binding protein

60
Q

What kind of bacteria is S. Aureus?

A

Gram positive

61
Q

How can an organism get around being affected by an antibiotic such as penicillin?

A

Change the pathway, e.g. use a different or modified transpeptidase enzyme

  • don’t have peptidoglycan
  • Produce an enzyme that stops it from working
  • grow very slowly or not at all
    • if not synthesizing peptidoglycan, it won’t be affected
  • pump the drug out before it accumulates to a high enough level inside the cell
62
Q

How do some bacteria have resistance to B-lactamase?

A
  • Some bacteria secrete a B-lactamase (an enzyme that lyses the B-lactam antibiotic)
  • Inactivation of the antibiotic by the enzyme —> no effect on the transpeptidase enzyme —> normal cross-linking and bacterial growth
63
Q

Why do we have problems of resistance?

A
  1. Inclusion of antibiotics in animal feed as a growth supplement
  2. Inappropriate use/prescription of antibiotics by physicians
  3. Poor patient adherence to treatment regimes
  4. Self medication with black market medications
  5. Use of standard/improperly stored antibiotics
  6. Natural bacterial response to a harmful selective pressure
64
Q

Why is it important assess antimicrobial activity in clinical settings?

A

-prevents unnecessary use of ineffective, expensive and/or compounds with side effects

  • Helps guide treatment decisions
    • tests that help determine what works and at what concentration:
  • MIC
  • Disk diffusion assay
  • PCR for specific resistance genes
65
Q

Describe MIC( minimum inhibitor concentration) broth dilution method

A

MIC= 1st tube without visible growth

Plate out onto agar

MBC- plate without visible colonies

66
Q

Describe eTest strips

A
  • Another way to determine the MIC
  • Plastic strip with graded concentrations of antibiotic
  • Area where growth touches the strip is the MIC
67
Q

Describe the Disk-Diffusion (Kirby-Bauer Technique)

A

-Bacteria are inoculated onto surface of a special type of media

  • Discs containing set concentrations of antibiotic are added:
    • antibiotic diffuses out from the disc:
      • close to the disc= highest concentration
      • further away= lower concentration

-plates are incubated

-Zones of inhibition (clearing) measured
-the larger the zone, the more sensitive the bacteria are
Because lower concentrations of antibiotics are inhibiting them

68
Q

What are the multiple factors that determine whether microorganisms are impacted by a treatment?

A

Population size: larger the population, the longer it will take for the effect to be shown

Population composition: microbes differ in terms of susceptibility and also, presence of endospores increase time required

Time exposure

D. Environmental conditions-temperature, presence of organic matter(blood, pus, etc) and pH

69
Q

What does sterilization mean?

A

Making something free of living microorganisms

70
Q

What is a disinfectant?

A

A chemical liquid that destroys all pathogenic organisms except spores(May or may not be destroyed)

71
Q

What is pasteurization?

A

The partial sterilization of a product, like wine or millk, to make it safe for consumption and improve its keeping quality

72
Q

What does antisepsis mean?

A

Prevention of infection by inhibiting growth. Implies scrupulously clean of all living organisms

73
Q

What disinfectants can destroy endospores?

A

Hydrogen peroxide, formaldehyde, chlorine, gluteraldehyde

74
Q

What are the 2 most resistant microganksms?

A

Prions the most, endospores, the least

75
Q

What microbes are the most sensitive?

A

Gram positive the second most sensitive

Envelopes virus the most

76
Q

How are inert surfaces cleansed?

A

Physical- non ionizing radiation,

Chemical- disinfectants

77
Q

How are lab and surgical equipment cleansed?

A

Physical- autoclave/heat and ethylene oxide

Chemical-certain disinfectants

78
Q

How are lab media cleansed?

A

Autoclave and filtration

79
Q

How is skin cleansed?

A

Chemical- antiseptics

Therapeutic- topical antimicrobials

80
Q

How are mucus membranes cleansed?

A

Antiseptics and antimicrobials

81
Q

How are tissues and organs cleansed?

A

Antimicrobials

82
Q

What is the function and active components in listerine?

A

Active components- eucalyptol, menthol, methyl salicylate and thymol

Action- bacterial cell wall destruction

Bacterial enzymatic inhibition

Extraction of bacterial LPS1

83
Q

What are the active components and function of Savlon?

A

Active components- cetrimide, chloroexidine, gluconqte

Function- quarternary ammonium compound

84
Q

What are the active components of detox and it’s main functions?

A

Active components- chloroxyleno
Action-disrupt cell membranes

In activation of proteins

Microbiology PMY 3 (24 decks)

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