CH. 7: The Control of Microbial Growth Flashcards
1
Q
ignaz semmelweis/joseph lister
A
first efforts on microbial control (~100 years ago)
2
Q
methods of control (2)
A
physical
chemical
3
Q
sepsis:
A
refers to microbial contamination
4
Q
asepsis:
A
the absence of significant contamination
5
Q
sterilization:
A
removing ALL microbial life
via heating and filtration
6
Q
sterilant:
A
sterilizing agent
7
Q
commercial sterilization (and procedure):
A
killing C. botulinum endospores (via heating)
8
Q
disinfection:
A
removing/destroying pathogens (vegetative cells, NOT endospores)
9
Q
antisepsis:
A
removing pathogens from (disinfection of) LIVING TISSUE
10
Q
degerming:
A
removing microbes from a limited area
- *mechanical removal**
e. g. alcohol swabs
11
Q
sanitization:
A
lowering microbial counts to levels safe for public health and to minimize disease transmission
12
Q
biocide/germicide:
A
killing microbes (NOT endospores)
13
Q
bacteriostasis:
A
INHIBITING, not killing, microbes
i.e. stops growth temporarily
14
Q
rate of microbial death?
A
bacterial populations tend to die at a constant rate
15
Q
effectiveness of antimicrobial treatment depends on:
A
- number of microbes
- environment
- time of exposure
- microbial characteristics
16
Q
[# of microbes] larger populations…
A
take longer to eliminate
17
Q
[environment] organic matter…
A
inhibits antimicrobial chemicals
18
Q
[environment] temperature:
A
disinfectants work better in warmer environments
19
Q
[environment]
A
biofilms
fat/proteins protect microbes when heat treated
acidic conditions are favourable for disinfectants
20
Q
[time of exposure]
A
extended exposure time is more effective against resistant microbes or endospores
21
Q
[microbial characteristics] gram positive…
A
gram + bacteria more susceptible than gram negative (due to lipopolysaccharide in gram negative cell wall)
22
Q
actions of microbial control agents (3)
A
- alteration of membrane permeability
- damage to proteins
- damage to nucleic acids
23
Q
[actions of microbial control agents]
alteration of membrane permeability
A
–> target phospholipids and proteins to cause leaks in plasma membrane
24
Q
[actions of microbial control agents]
damage to proteins
A
–> heat and chemicals can denature enzymes (hydrogen bonds are more easily destroyed than covalent bonds)
25
[actions of microbial control agents]
| damage to nucleic acids
- -> heat, chemicals, radiation can damage DNA/RNA thus interfering with vital functions (replications, metabolic enzymes)
- -> often lethal to microbial cells
26
Heat
- used to sterilize (lab media, glassware, hospital instruments, preserve canned food)
- - DENATURES & INACTIVATE PROTEINS
27
resistance of microbes to heat treatment is assessed by:
thermal death point (TDP) and thermal death time (TDT) (these give an idea of severity of treatment to kill a population of bacteria)
28
thermal death point (TDP):
lowest temperature at which cells in a culture are killed IN TEN MINUTES.
29
thermal death time (TDT):
minimal time during which ALL CELLS in a culture are killed at a given temperature.
30
decimal reduction time (DRT):
minutes required to kill 90% of a population at a given temperature
31
moist heat sterilization
DENATURES proteins
boiling for 10 mins = kills vegetative forms of bacteria, fungi, and their spores, and most viruses
(not perfect for sterilization - some viruses, endospres can resist boiling for a long time)
32
(moist heat sterilization) autoclave
steam under pressure
| @ 15 psi & 121C: all organisms AND endospores in contact will die within 15 minutes
33
steam sterilization, steam must...
contact item's surface
34
pasteurization
reduces spoilage organisms and pathogens
35
equivalent tx to pasteurization
30 mins at 63C
36
high-temperature short-time pasteurization:
72C for 15 seconds for milk
- - thermoduric organisms survive
- unlikely to cause disease
37
ultra-high-temperature sterilization:
140C for <1 sec for milk
38
dry heat sterilization
kills by OXIDATION
- - dry heat
- - flaming
- - incineration
- - hot-air sterilization = longer time than moist heat because it takes longer for heat in air to be transferred to a cold body (ie. hot air needs 170C for 2 HRS; autoclave needs 121C for 15 mins)
39
filtration
- - used for heat sensitive materials
| - - passage of liquid or air through a screen-like material with pores small enough to catch intended target
40
HEPA filter removes microbes
>0.3 um
41
Membrane filtration removes microbes
>0.22 um
42
physical methods of microbial control (3)
lower temperature/quick freezing
high pressure
dessication
osmotic pressure
43
[physical control] low temperature
inhibits microbial growth
- - refigeration is generally bacteriostatic
- - deep-freezing
- - quick freezing will usually make bacteria dormant (a slow thaw will do more damage)
44
[physical control] high pressure
denatures proteins and carbohydrates
| -- preserves flavours, colours, and nutrients
45
[physical control] dessication
prevents metabolism but DOES NOT KILL immediately
- - lyophilization (freeze-drying)
- - no effect on endospores or viruses
46
[physical control] osmotic pressure causes..
plasmolysis
| -- NOT effective against moles
47
radiation effect depends on (3)
wavelength
intensity
duration
48
ionizing radiation mechanism
ionizes water to release OH hydroxyl (funny little dot thing)
damages DNA
49
ionizing radiation examples
x-rays, gamma rays, electron beams
50
nonionizing radiation mechanism
damages DNA
51
nonionizing radiation example
UV, 260 nm
52
microwaves kill by
heat; not especially antimicrobial
53
ionizing radiation
have shorter wavelength - usually <1nm
| have more energy
54
ionizing radiation used in sterilization of
pharmaceuticals
disposable dental and medical supplies -- plastic syringes, gloves, suturing materials, catheters
some foods (low-level ionizing radiation)
55
ionizing radiation target theory of damage
- - passage of radiation through cellular structures = called a hit
- - one or few hits cause nonlethal mutations
- - many hits are likely to cause sufficient deleterious mutations
56
nonionizing radiation
longer wavelength (e.g. UV)
- damages DNA by formation of covalent bonds between adjacent pyrimidines, usually thymines (forms thymine dimers)
- thymine dimers interfere with DNA replication
- most effective wavelength for killing bacteria is 260 nm
- UV lamps used in hospital rooms, nurseries, operating rooms, cafeteria
- used to disinfect vaccines and certain medical products
- UV not very penetrating, so organism must be directly exposed to it
- disadvantage: can damage our eyes, cause burns and skin cancer
- UV from sun has shorter damaging wavelength but it's filtered by ozone layer
- microbial pigments may also protect from sun
57
chemical methods of microbial control
few achieve sterility
-- most reduce populations to safe levels or remove vegetative vells of pathogens
no one single disinfectant is appropriate for all situations
58
5 principles of effective disinfection
1. concentration of disinfectant
2. organic matter
3. pH
4. ability of disinfectant to contact microbe
5. time
59
two methods for testing disinfectant effectiveness
1. use-dilution test (recommended)
| 2. disk-diffusion method (used in teaching labs)
60
use-dilution test
- metal cylinders dipped in test bacteria then dried
- dried cultures are placed in disinfectant for 10 min at 20C
- cylinders are transferred to culture media to determine whether bacteria survived treatment
61
phenol and penolics
disrupt plasma membranes
- remain active on surfaces for longer periods and when in contact with organics
- effective on Mycobacterium tuberculosis
- suitable for pus, saliva and feces
62
phenol
- first used by Lister
- was effective at controlling sewage odour
- >1% concentration has significant antimicrobial effects
63
phenolics
less irritating or increased activity
64
bisphenols
also disrupt plasma membranes
65
(bisphenol) hexachlorophene
- used in hospitals (surgeries, nurseries)
| - prescription lotion
66
(bisphenol) triclosan
- soaps
- toothpaste
- incorporated into kitchen equipment (knife handles, cutting boards)
- resistance is being reported
- inhibits an enzyme affecting lipid synthesis
67
biguanides mechanism
primarily disrupt plasma membranes
68
(bisguanides) chlorhexidine
- used on skin and mucous membranes
| - in alcohol or detergent solution, can be used for surgical hand scrubs and pre-op skin preparation
69
(bisguanides) alexidine
- more rapid
70
(halogen) iodine
- very effective: works against all bacteria, many endospores, some fungi and viruses
- alter protein synthesis and membranes by complexing amino acids and unsaturated fatty acids
71
(iodine) Tinctures
in aqueous alcohol
72
(iodine) Iodophores
in organic molecules, e.g. Betadine
73
(halogen) chlorine
- hyochlorous acid (HOCl) formed with water
CHLORAMINE: chlorine + ammonia
--> is less effective than hypochlorite but long-lasting
- oxidizing agents, prevents enzymes from functioning
- effective against cysts and endospores at higher concentrations
- widely used (municipal systems, swimming pools, surface disinfectant)
74
alcohols
- kills bacteria and fungi, enveloped viruses
- ethanol (70% is optimal), isopropanol (denature proteins, dissolve lipids, requires water)
- not really useful as an antiseptic
- enhance effects of other chemical agents
75
metals and what kind of action?
- Ag, Hg, Cu, and Zn
| - have Oligodynamic action (denatures proteins)
76
silver sulfadiazine used
as a topical cream on burns
77
copper compounds used
as either an algicide or antifungal agent
78
Hg used
as an antifungal agent in paints
79
Zn is used
as an antimicrobial put into some construction materials, mouthwashes, and antidandruff shampoos
80
[surfactants/surface-active agents]
| soap:
mechanical (emulsification)
| degerming
81
[surfactants/surface-active agents]
| acid-anionic detergents:
- anion reacts with plasma membrane
| - sanitizing and nontoxic
82
[surfactants/surface-active agents]
| quaternary ammonium compounds (cationic detergents):
- denature proteins, disrupt plasma membrane
| - bactericidal, virucidal (enveloped viruses), fungicidal, amebicidal
83
[chemical food preservatives]
| organic acids and their salts:
- inhibit metabolism
- sorbic acid, sodium benzoate, calcium proprionate
- -> control molds and bacteria in foods and cosmetics
84
[chemical food preservatives]
| nitrate (from NaNO3 and NaNO2) prevents..:
endospore germination in meats (controls botulism)
85
[chemical food preservatives]
| antibiotics in food
Nisin and natamycin prevent spoilage of cheese
86
aldehydes
- very effective
- inactivate proteins by covalent cross-linking with functional groups (-NH2, -OH, -COOH, -SH)
- Glutaraldehyde and ortho-phthalaldehyde (use: medical equipment)
- formaldehyde gas
87
gaseous sterilants
- used in a closed chamber
- cross-linking of nucleic acids and proteins
- use: heat-sensitive material (ethylene oxide)
88
plasma
- gas excited by electromagnetic field
- free radicals destroy microbes, even endospores
- use: tubular instruments (e.g. scopes)
89
supercritical fluids
- compressed CO2 with gaseous and liquid properties
| - use: medical implants and food
90
peroxygens
- oxidizing agents
| - use: contaminated surfaces (O3, H2O2, peracetic acid, benzoyl peroxide)
91
[peroxygens] gaseous hydrogen peroxide (H2O2) use
sterilize hospital rooms
92
[peroxygens] peracetic acid use
powerful sterilant and leaves no toxic residues, just water and acetic acid, and can be used on food
93
[peroxygens] ozone (O3) use
supplements chlorine, too reactive to use on its own
94
order of microorganisms from most resistant to least resistant to CHEMICAL biocides:
```
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
```
95
_____ (chemical antimicrobial) is most effective against endospores and mycobacteria
Glutaraldehyde
