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Medical Microbiology > Chapter 7 - Control of Microbial Growth > Flashcards

Chapter 7 - Control of Microbial Growth Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

What is sterilization, its common application, and common agents?

A

Destruction or removal of all forms of microbial life, including endospores and viruses from an inanimate item

Application: Preparation of surgical equipment and of needles used for injection

Agents: Pressurized steam (autoclave), chemicals, and radiation

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2
Q

What is commercial sterilization?

A

Sufficient heat treatment to kill endospores of C. botulinum in canned food

More resistant endospores of thermophilic bacteria may survive, but they will not germinate and grow under normal storage conditions

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3
Q

What is disinfection, its common application, and common agents?

A

Destruction or reduction of vegetative pathogens on inanimate objects through application of heat or antimicrobial chemicals

Application: Cleaning surfaces like laboratory benches, clinical surfaces, and bathrooms

Agents: Chlorine bleach, phenols (Lysol), glutaraldehyde

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4
Q

What is antisepsis, its common application, and common agents?

A

Destruction or reduction of vegetative pathogens on living tissue through application of an antimicrobial chemical

Application: Cleaning skin broken due to injury; cleaning skin before surgery

Agents: Boric acid, isopropyl alcohol, hydrogen peroxide, iodine (betadine)

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5
Q

What is degerming, its common application, and common agents?

A

Reduces microbial load on skin or tissue through gentle to firm scrubbing and the use of mild chemicals

Application: Handwashing

Agents: Soap, alcohol swab

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6
Q

What is sanitization, its common application, and common agents?

A

Reduces microbial load of an inanimate item to safe public health levels through application of heat or antimicrobial chemicals

Application: Commercial dishwashing of eating utensils; cleaning public restrooms

Agents: Detergents containing phosphates, industrial-strength cleaners containing quaternary ammonium compounds

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7
Q

What does bacteriostatic mean?

A

Inhibit the growth and multiplication of bacteria

Once bacteriostatic is removed, growth could resume

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8
Q

What does bactericidal mean?

A

Kills bacteria

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9
Q

What is decimal reduction time (DRT)?

A

Time it takes to kill 90% of the population (1 - log decrease in total population) when exposed to a specific microbial control protocol at a specified temperature

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10
Q

How is decimal reduction time used in sterilization?

A

Determines effectiveness - Lower DRT indicates a faster reduction of microbial population, meaning it is more efficient

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11
Q

What 4 factors influence the effectiveness of antimicrobial treatments?

A

Number of microbes
- The more microbes there are to begin with, the longer it takes to eliminate the entire population

Environmental influences (organic matter, temperature, biofilms)
- Concentration of disinfecting agent or intensity of exposure is important
- Higher temperature and higher concentrations of disinfectants kill microbes more quickly and effectively
- Presence of bodily fluids, tissue, organic debris, or biofilms limit contact between the agent and targeted cells, which increases the cleaning time or intensity of the microbial control protocol required to reach the desired level of cleanliness

Time of exposure
- Longer exposure times kill more microbes

Microbial characteristics
- Susceptibility of the microbe to that disinfecting agent or protocol

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12
Q

What should be considered when choosing a microbial control agent?

A

Cheap, fast, stable, and not harmful

Consider:
- Site to be treated
- Relative susceptibility
- Environmental conditions

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13
Q

What are the 3 levels of germicide?

A

High - all microbes plus spores

Intermediate - vegetative pathogens, fungal spores, protozoans

Low - vegetative only

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14
Q

What are the 3 mechanisms by which agents kill or inhibit microbes?

A

Damage to proteins:
- Proteins regulate everything (metabolism) - denaturing proteins/enzymes disrupts cell function

Damage to nucleic acids:
- Direct protein synthesis and replication (mutate = deadly) - destroy or damage is fatal

Alter the cytoplasmic membrane or cell wall:
- Cell wall counteracts the effect of osmosis (prevent bursting) - disruption makes cells more vulnerable
- Cytoplasmic membrane - controls passage of things in and out (disruption of lipid and proteins = inside leaks out)

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15
Q

How does heat kill microbes?

A

Denatures DNA in proteins

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16
Q

What is thermal death point (TDP)?

A

Lowest temperature at which all cells in a culture are killed in 10 minutes

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17
Q

What is thermal death time (TDT)?

A

Time during which all cells in a culture are killed at a specific temperature

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18
Q

Compare the effectiveness of moist and dry heat

A

Moist heat penetrates better, so it is more effective

Water conducts heat better than air, so the temperature will be distributed better in moist heat methods, making it a better method

Moist heat denatures proteins while dry heat kills by oxidation effects

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19
Q

What are the 3 methods of moist heat and how do they kill microbes?

A

Boiling: Protein denaturation
- Does not kill all microbes (spores and viruses are not always killed)
- Kills within 10 minutes, sometimes up to 30 minutes for heartier microbes
- Easily accessible

Autoclaving: Protein denaturation
- Pressurized steam - most dependable
- Sterilizing agent is steam, not pressure
- All vegetative cells and their spores are killed in about 15 minutes
- Limitations: plastics, degrade chemicals, oils don’t mix with water

Pasteurization: Protein denaturation
- Reduces spoilage organisms and pathogens
- Not all are killed - those who withstand heat survive
- Batch method - 63℃ for 30 minutes
- High-temperature short-time - 72℃ for 15 seconds
- Ultra-high-temperature pasteurization - 135℃ for 1 second
- Ultra-high temperature sterilization - 140℃ (kills all)

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20
Q

What are the 3 methods of dry heat and how do they kill microbes?

A

Direct flaming: Burning contaminants to ashes
- Very effective for sterilization
- Used for inoculating loops

Incineration: Burning to ashes
- Very effect for sterilization
- Used for disposal of contaminated dressings, animal carcasses, and paper

Hot-air sterilization: Oxidation
- Very effective for sterilization
- Requires temperature of 170℃ for 2 hours
- Used for empty glassware that is placed in an oven

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21
Q

How does filtration suppress microbial growth?

A

Separation of bacteria from suspending liquid

High-efficiency particulate air (HEPA) filters - remove microbes from the air

Membrane filters - remove microbes from liquids

Removes microbes by passage of a liquid or gas through a screenlike material

Most filters in use consist of cellulose acetate or nitrocellulose

Useful for sterilizing liquids that are destroyed by heat (i.e., enzymes, vaccines)

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22
Q

What are the 3 methods of cold temperatures and how do they suppress microbial growth?

A

Refrigeration: decreased chemical reactions and possible changes in proteins
- Has bacteriostatic effect (slows growth)

Deep-freezing: Decreased chemical reactions and possible changes in proteins
- Effective for preserving microbial cultures, food, and drugs

Lyophilization: Decreased chemical reactions and possible changes in proteins
- Most effective for long-term preservation of microbial cultures, food, and drugs

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23
Q

How does high pressure suppress microbial growth?

A

Alteration of molecular structure of proteins and carbohydrates

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24
Q

How does desiccation suppress microbial growth?

A

Disruption of metabolism

Involves removing water from microbes

Primarily bacteriostatic

When water is made available, they can resume growth and division

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25
Q

How does osmotic pressure suppress microbial growth?

A

Plasmolysis

High concentrations of salts and sugars results in hypertonic environment that causes a loss of water from microbial cells

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26
Q

What are the 3 types of radiation and how do they kill microbes?

A

Ionizing radiation: Destruction of DNA
- Uses gamma rays, X rays, and high-energy electron beams
- Ionizes water to create reactive hydroxyl radicals
- Damages DNA by causing lethal mutations
- Kills all
- Used for sterilizing pharmaceuticals and medical and dental supplies

Nonizonizing radiation: Damages to DNA
- UV light
- Damages DNA by creating thymine dimers that inhibit correct replication during cell reproduction
- Damages but doesn’t kill spores
- Not very penetrating

Microwaves: Heat
- Not much of a direct effect
- Heat kills most vegetative pathogens

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27
Q

What are vegetative pathogens?

A

Growing form of bacteria

Not spore form

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28
Q

Is radiation safe to use on food?

A

Yes - process does not make food radioactive

Radiation passes through the food, killing germs without leaving residual radiation

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29
Q

How does pasteurization differ from other types of moist heat microbial control?

A

Generally uses mild temperatures compared to autoclaving and boiling (63-72 degrees vs. 121 degrees) - exception is ultra-high temperature pasteurization/sterilization that is 135-140 degrees (not often used)

Primary goal is to kill pathogens and reduce number of spoilage microbes, whereas other methods aim for sterilization and killing all microbes

Commonly used in dairy products and other beverages in order to make them safe for consumption, while other methods are used in medical and laboratory settings to sterilize equipment and materials

30
Q

What 5 factors can affect the efficacy of a disinfectant?

A

Concentration of disinfectant

Temperature - activity of disinfectant increases as temperature increases, but too high temperature can inactivate it

Presence of organic materials - can interfere with action of disinfectant

pH of medium - certain disinfectants work optimally at different pHs

Contact with microbes - area may need to be scrubbed and rinsed before disinfectant is applied in order to make effective contact

31
Q

What are the 3 levels of disinfectants?

A

Low level: kills some viruses and vegetative bacteria (quaternary ammonium compounds)

Intermediate level: kills mycobacterium, most viruses, and all vegetative bacteria (phenolics, halogens, diluted alcohols)

High level: kills all organisms except high levels of bacterial spores and prions (ethylene gas, formaldehyde, glutaraldehyde, hydrogen peroxide)

32
Q

What are the 5 methods for evaluating disinfectants and antiseptics?

A

Phenol coefficient

Use-dilution test

In use test

Disk-diffusion

Minimum inhibitory concentration

33
Q

What are the steps for a phenol coefficient?

A

Dilute concentration of phenol and see how long it takes to kill organisms in 10 minutes but not 5 minutes

Also dilute disinfectant concentration to see how long it takes to kill organisms in 10 minutes but not 5 minutes

Then divide disinfectant concentration by phenol concentration to see phenol coefficient

34
Q

What is the protocol for a use-dilution test?

A

Current standard in US

Utilize 3 bacteria in lab test

Metal rings dipped in pure culture

Dried at 37 degrees

Rings placed in disinfectant for 10 minutes at 20 degrees

Rings placed on media - count number of colonies grown

35
Q

What is the protocol for an in use test?

A

Swab area before and after cleaning

Inoculate broth

See if it grows

36
Q

What is the protocol for a disk-diffusion test?

A

Evalutates efficacy of chemical agents

Filter paper disks are soaked in a chemical and placed on a culture

Look for zone of inhibition around disks

37
Q

What is the protocol for a minimum inhibitory concentration test?

A

Serial dilutions of an antimicrobial agent of known concentration

Inoculate and incubate the tubes

MIC is lowest concentration of antimicrobial agent needed to inhibit growth

After determining MIC, plate bacteria in tubes where there was no growth and put them on a nutrient agar plate and see if anything grows to determine if bactericidal or bacteriostatic
- MBC - minimum concentration that kills bacteria

38
Q

What is the recommended optimal concentration of alcohol to kill bacteria?

A

70% ethanol

39
Q

What are the 4 targets for a chemical antimicrobial?

A

Cell walls, cytoplasmic membranes, proteins, or DNA

40
Q

How are different microbes affected by disinfectants?

A

Often more effect against enveloped viruses and vegetative cells of bacteria, fungi, and protozoa (endospores harder to kill)

Enveloped viruses have a lipid layer outside – easier to desiccate

Non-enveloped viruses have protein layer outside – harder to kill

Gram+ easier to kills than Gram- because of the presence of an outer membrane in Gram-

41
Q

What is the order of resistance of microbes to chemical biocides from most resistant to least resistant?

10 total

A

Prions

Endospores of bacteria

Mycobacteria

Cysts of protozoa

Vegetative protozoa

Gram-negative bacteria

Fungi, including most fungal spores

Viruses without envelopes

Gram-positive bacteria

Viruses with lipid envelopes

42
Q

What are examples of halogens, its mechanism, and applications?

A

Examples: Chlorine, iodine

Mechanism: Denatures proteins

Applications: Water treatment, skin antisepsis

43
Q

What are examples of phenolics, its mechanism, and applications?

A

Examples: Triclosan, chlorohexidine

Mechanism: Denature proteins, disrupt cell membranes

Applications: Surface disinfection, skin antisepsis

44
Q

What are examples of alcohols, its mechanism, and applications?

A

Examples: 70% ethanol, 75% isopropyl

Mechanism: Denatures proteins, dissolves lipids, dehydrating agent

Applications: Instrument disinfection, skin antisepsis

45
Q

What are examples of quaternary ammonium compounds, its mechanism, and applications?

A

Examples: Cationic detergents

Mechanism: Disrupt lipids in cell membrane

Applications: Instrument disinfection and skin antisepsis

46
Q

What are examples of heavy metals, its mechanism, and applications?

A

Examples: Mercury, copper, silver

Mechanism: Denatures proteins

Applications: Skin antisepsis, disinfectants, algaecide in pool and water supply, antiseptic in eyes

47
Q

What are examples of peroxides, its mechanism, and applications?

A

Examples: Benzoyl peroxide, hydrogen peroxide

Mechanism: Denatures proteins, radicals attack DNA, lipids, and proteins

Applications: Skin antisepsis, surface disinfection, contact sterilization

48
Q

What are examples of aldehydes, its mechanism, and applications?

A

Examples: Glutaraldehyde, formaldehyde

Mechanism: Denatures proteins, inactivates nucleic acids

Applications: Sterilize surgical equipment, embalming, vaccine production

49
Q

What are examples of sterilizing gases, its mechanism, and applications?

A

Example: Ethylene oxide gas

Mechanism: Denatures proteins, inactivates nucleic acids

Applications: Sterilize surgical equipment, heat sensitive objects

50
Q

How do bisphenols work?

A

Disrupt plasma membrane

51
Q

How do biguanides work?

A

Disrupt plasma membrane

52
Q

What are the 3 types of surface active agents?

A

Soaps and detergents

Acid-anionic sanitizers

Quaternary ammonium compounds

53
Q

How do soaps and detergents work?

A

Mechanical removal of microbes through scrubbing

54
Q

How do acid-anionic sanitizers work?

A

Disrupt plasma membrane

55
Q

What are the 2 types of food preservatives?

A

Organic acids

Nitrates/nitrites

56
Q

How do organic acids work?

A

Metabolic inhibition

Mostly affecting molds

Action not related to acidity

57
Q

How do nitrates/nitrites work?

A

Active ingredient is nitrite, which inhibits certain iron-containing enzymes of anaerobes

58
Q

What is selective toxicity?

A

An antimicrobial’s ability to selectively find and destory pathogens without damaging the host

Targets: Cell wall synthesis and ribosomes

59
Q

What is chemotherapy?

A

The use of chemicals to treat a disease

60
Q

What is an antibiotic?

A

A substance produced by a microbe that, in small amounts, inhibits another microbe

61
Q

What is an antimicrobial drug?

A

Synthetic substance that interferes with the growth of microbes

62
Q

What are broad spectrum antibiotics?

A

Antibiotics that affect a broad range of Gram-positive and Gram-negative pathogenic bacteria

63
Q

What are narrow spectrum antibiotics?

A

Antibiotics that target very specific types of bacteria

64
Q

What are the 5 modes of action of antibiotics?

A

Inhibition of cell wall synthesis

Inhibition of protein synthesis

Inhibition of nucleic acid synthesis

Injury to plasma membrane

Inhibition of essential metabolite synthesis

65
Q

How do antibiotics inhibit cell wall synthesis?

A

Penicillin prevents synthesis of peptidoglycans (beta-lactams)

Vancomycin binds PG subunits

Cell wall is greatly weakened, and the cell undergoes lysis

66
Q

How do antibiotics inhibit protein synthesis?

A

Inhibits translation by targeting bacterial 70S ribosomes (30S or 50S subunit)

67
Q

How do antibiotics inhibit nucleic acid synthesis?

A

Interfere with DNA replication and transcription (RNA polymerase)

Rifamycin inhibits RNA synthesis

68
Q

How do antibiotics injure plasma membranes?

A

Polypeptide antibiotics change membrane permeability

Antifungal drugs combine with membrane sterols

69
Q

How do antibiotics inhibit essential metabolite synthesis?

A

Antimetabolites compete with normal substrates for an enzyme

Often inhibit enzymes

70
Q

What are the 3 tests for antibiotic effectiveness?

A

Disk-diffusion method (Kirby-Bauer test)
- Tests effectiveness of chemotherapeutic agents
- Paper disks with agent placed on agar containing organism
- Zone of inhibition around the disk determines sensitivity of organism to antibiotic

E test
- Determines MIC
- Gradients of certain antibiotic concentrations are on a strip so you can see what concentration is effective

Broth dilution tests
- Determine MIC and MBC of antibiotic
- Test organism is placed into wells of a tray containing dilutions of a drug - growth is determined
- Antibiograms - reports that record susceptibility of organisms encountered clinically

71
Q

What are the 5 clinical considerations in prescribing antibiotics?

A

Routes of administration
- Topical for external infections
- Oral routes are self-administered and no needles
- Intramuscular delivers drug via needle into muscle
- Intravenous delivers drug directly into bloodstream

Toxicity
- Cause of adverse reactions is poorly understood
- Drugs can be toxic to kidneys, liver, or nerves
- Considerations for pregnant women
- Therapeutic index - ratio of drug dose that can be tolerated to the drug’s effective dose

Allergies
- Allergic reaction are rare but can be life-threatening
- Anaphylactic shock

Disruption of normal microbiota
- May result in secondary infections
- Overgrowth of normal flora causing superinfections
- Greatest concern in hospitalized patients

Overuse and misuse of antibiotics
- Antibiotic resistance

Medical Microbiology (4 decks)

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