Transcript Physical and Chemical Control of Microorganisms

Physical and Chemical Control of
Microorganisms
I. Terms
II. Factors which determine the effectiveness
of control methods
III. Methods of physical control
IV. Chemical agents
Terms
1) “Control” -- Limiting exposure to
_______________________ agents

Microorganisms are part of our environment

Infection can be controlled by limiting exposure to infectious
agents
2) _______________ -- Removal or destruction of all
_________________ microorganisms. “sterile”
3) Disinfection -- Removal or destruction of pathogens
from ________________________ areas. “disinfectant”
4) Antisepsis -- Removal or destruction of vegetative forms
from _______ _____________. “antiseptic”
Note: Antiseptics and disinfectants do the same thing, but in different environments
Terms (continued)
5) Sanitization -- any cleansing technique that
mechanically removes microorganisms. Usually
soaps
More terms
6) “-cide” refers to
______________.
“Bacteriocide” kills
bacteria,
“fungicide” kills
fungi, etc.
7) “-static” means ‘to stand
still’. Refers to an agent
which prevents
_______________ but
doesn’t kill.
“Bacteriostatic” or
“fungistatic” or
“virustatic” agent
Factors which determine the
effectiveness of a control method
1. The number of microorganisms
“Death curve”
107
106
# of
105
________ 104
cells
Note log scale on y axis
(each increment is 10X
reduction in numbers)
103
102
101
100
1
2
3 4 5
Time (min.)
6
7
8
107
106
105
104
103
102
101
100
1
2
3 4 5
Time (min.)
6
7
8
Decimal reduction time (DRT) -- Time for a _____
reduction in population size. Here DRT = ______
If the goal is to reduce numbers to 102 then the size of the initial
population will determine how long it will take, in this case,
____________ minutes.
Factors which determine the
effectiveness of a control method (cont.)
Spore formers vs. non-spore formers
107
106
# of
105
viable
4
cells 10
103
102
101
100
__________________
Vegetative
cells
1
2
3 4 5
Time (min.)
6
7
8
Factors which determine effectiveness of
a control agent (cont.)
•
Temperature and _______ of the environment
•
___________________ of the agent
•
Mode of action of the agent
•

Microbistatic vs. microbicidal

Cellular target
Presence of ________________ compounds or
inhibitors of the control agent
Methods of Physical Control: Heat
_________ heat
 Hot
water, boiling water, steam
 60° - 135° C
 Denatures proteins, nucleic acids
__________ heat
 Ovens
 160°
- >1000° C
 Denatures, oxidizes
At lower temperatures, moist heat is __________ effective than dry heat
Moist heat methods
I. Boiling water -- ________ min. boiling kills all
vegetative cells
II. Pasteurization -- Heating to temp. below boiling to kill
specific pathogens and increase shelf-time

Batch method -- 63°-66° for 30 min.

___________ method -- 71.6° for 15 sec.
Results in killing of most viruses and 97-99% reduction in veg. stages
of bacteria and fungi

UHT (Ultra High Temp) -- 134° 1-2 ___________.
Milk can last up to 3 months unrefrigerated
Primary pathogen targets of pasteurization: ______________,
Listeria, Mycobacterium, Campylobacter, Brucella
Moist heat methods (cont.)
III. Steam under pressure

Highest temp. of moist heat at sea level -- _________° C

If ____________ increased, higher temps. can be reached
Autoclaving
Commonly:
_______° C at
15 PSI
________ min. at
this temp. is
very effective
Effects on cellular proteins
Text, Fig. 11.4
Physical methods: radiation
Physical methods: radiation
____________ -- knocks
electrons off atoms --> ions
e.g. gamma rays, x-rays
 Damages
DNA and
proteins by breaking bonds
-- Fig. 11.8
 Exposure hazard to
humans
 Penetrates ___________
and liquids
 Used in fruits &
vegetables, now meats
Non-ionizing -- excites
atoms but doesn’t ionize
e.g. ____________,
sunlight
 Damages DNA by
creating T-T dimers -Fig. 11.8, 11.10
 Relatively safe to use
 Doesn’t penetrate
solids or liquids well
 ______________
sterilization, water
treatment
Text, Fig. 11.8
Text, Fig. 11.10
Other physical control methods
Sonication -- Disruption using ___________ waves
Filtration
Text, Fig. 11.13
Chemical control agents
I. Many kinds but most function by:
 Disrupting
 Altering
__________________
________________ and/or nucleic
acid structure
II. Effectiveness is determined by:
 Concentration
 Contact
time
Major groups
•
•
•
•
•
•
________________
Phenol and its derivatives
Alcohols
Hydrogen peroxide
Detergents
Heavy ___________
Halogens
•
Mainly _______________, also iodine and fluorine
•
Iodine “iodophors” most common iodine compound used
in hospitals: Betadine, Povidone, etc. Less ____________
than free iodine due to slow release of free iodine.
•
3 Chlorine forms:
Cl2 (chlorine gas)
OCl (hypochlorite -- common ‘bleach’)
NH2Cl (chloramines)
In solution, these compounds combine with water to form hypochlorous
acid (HOCl). This is the active form which destroys by ____________
Effective against: bacteria, fungi, spores, viruses
Limitations:

ineffective at _____________ pH

______________: light and O2 cause breakdown
Phenols
p-cresol (lysol)
phenol
OH
OH
CH3
Hexachlorophene (phisohex)
OH
Cl
OH
CH2
Cl
Cl Cl
Cl
Cl
Phenolics affect
protein function
and/or disrupt
membranes
Alcohols
•
Ethanol -- 70% to 95%
•
Isopropanol -- more microbicidal but also
more __________
Destroy cell membranes, can coagulate
proteins
Hydrogen peroxide (H2O2)
Forms _______________ free radicals (e.g.
superoxides, hydroxyl radicals: see last
lecture) which are toxic to all cells
Also breaks down to H2O and O2, therefore is
strongly effective against _____________.
Detergents
All solubilize membranes and disrupt proteins
Text, Fig. 11.3
Detergents (cont.)
Two types: ___________ (charged) and non-ionic
Non-ionic and anionic detergents (like soaps) are not very
microbicidal, although they may be very effective in sanitization.
_____________ detergents (like benzalkonium chloride) are the
most effective ionic detergents.
Heavy metals
Mainly only mercury and silver preparations
are used now.
Merthiolate, mercurochrome, silver nitrate, etc.
Form ions which complex with cell
components, stopping growth
Disadvantages:
 _________________
 _________________
 Microbes
can develop ___________________