DMP 712 Bact Exam 1 Sterilization and Disenfection Section 5 Robertson
Terms
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- microbial death defn:
- irreversible loss of the ability to divide - probability of any one cell dying is constant per unit of time
- bacteriocidal defn:
- describes a compound/drug that kills bacteria
- bacteriostatic defn:
- describes a compound/drug that inhibits growth of bacteria
- sterilization defn
- the complete killing or removal of all living microbes from a growth medium
- disenfectant defn
- a chemical agent which causes death of microbes and reduces numbers, but does not produce a sterile environment
- biocide/germicide defn:
- refers to chemical agents that kill microbes
- sanitizers defn:
- only reduce the numbers of microbes on inanimate surfaces
- detergents defn:
- disperse and remove soil and organic material from surfaces and permit disenfectants to act
- thermal death point defn:
- the lowest temperature at which a 10 min exposure of a given volume of a broth culture results in sterilization
-
To kill a bacterial cell:
cause irreparable damage to its: (3) -
1) genome
2) envelope (g+ cell membrane or g- inner membrane and outer membrane)
3) inactivate/denature certain classes of proteins
=catabolic enzymes --> no energy
= biosynthetic enzymes --> no macromolecules
= structural proteins --> eg membrane - Disenfection goal:
- to reduce numbers, not produce a sterile environment
- Chemotherapy goal:
- kill all microbes
- Selective toxicity related to:
- 5 chemotherapy mechanisms with high to low selective toxicity
- Death Kinetics General Principles (3)
-
1) Fraction of microbes die during given interval
2) time to sterility depends on initial numbers
3) bacteria and viruses vary in susceptibility (g+ vs. g-, spores vs. vegetative cells) -
Death Kinetics:
Environmental conditions determine: -
Death Kinetics:
Environmental conditions determine: effectiveness of disenfectants -
Control of Microbial Growth
Protein Denaturation
moist heat (3 examples) -
1) boiling 100C 5-10min except spore formers
2) autoclave/pressure cooker 121C 2-3min vegetative 15 spore
3) flash pasteurization 71C 15sec -
Control of Microbial Growth
Protein denaturation
dry heat
temp:
time:
used for: -
Control of Microbial Growth
Protein denaturation
dry heat
temp: 160-170C
time:1-2hrs
used for:glassware and metal objects -
Control of Microbial Growth
Protein denaturation
Chemicals
effectiveness depends on (3):
Mechanisms (2): -
Control of Microbial Growth
Protein denaturation
Chemicals
effectiveness depends on (3): 1) concentration
2) time
3) temperature
Mechanisms (2):
1) disrupt protein water interactions with more protein protein interaction (aggregation and denaturation)
2) disrupt protein-lipid interaction (non-functional membrane) - Mechanisms of Chemical Disenfectants (5 mechanisms, 3 substances)
-
Mechanisms of Chemical Disenfectants (5 mechanisms)
1) denature proteins (alcohol)
2) denature proteins and bind phospholipids
3) denature proteins and lipids
4) denature lipids (alcohol)
5) alter membrane permeability (phenols) -
Control of Microbial Growth
Phenol
First used:
Importance to other disenfectants:
Common example: -
Control of Microbial Growth
Phenol
First used: antiseptic in surgery
Importance to other disenfectants: all compared to phenol ith phenol coefficient (PC)
Common example: Lysol - Calculate PC
-
Cpd a kills bacteria in 10 min dillution 1:450
phenol kills bacteria in 10 min dillution 1:90
PC = 450/90 = 5 -
Meaning of PC
PC > 1
PC = 1
PC < 1 -
Meaning of PC
PC > 1: more effective disenfectant
PC = 1: equally disenfectant
PC < 1: less effective -
Control of Microbial Growth
Disruption of Cell Membrane
Which 2 types of detergents? -
Control of Microbial Growth
Disruption of Cell Membrane
Which 2 types of detergents?
1) cationic detergents
2) anionic detergents -
Control of Microbial Growth
Disruption of Cell Membrane
Cationic detergents
works because:
group of compounds:
-mechanism:
-works against:
-example: -
Control of Microbial Growth
Disruption of Cell Membrane
Cationic detergents
works because: positive charge of detergent attracts negative charge on microbial cell surface
group of compounds: quaternary cpds e.g. benzylalkaonium chloride
-mechanism: some detergent action with disenfectant activity
-works against: most microbes, not spores
-example: Roccal D -
Control of Microbial Growth
Disruption of Cell Membrane
Anionic detergents
effectiveness vs. cationic:
example: -
Control of Microbial Growth
Disruption of Cell Membrane
Anionic detergents
effectiveness vs. cationic: less due to negative charge on microbial cell surface
example: sodium palmitate (skin antiseptic) -
Control of Microbial Growth by
oxidation of -SH Groups
reaction catalyzed by (2):
reaction: -
Control of Microbial Growth by
oxidation of -SH Groups
reaction catalyzed by (2): peroxidases and halogens
reaction:
R-SH + HS-R --> R-S-S-R'
(active) (active) (inactive) -
Modification of -SH Gropus
Reaction catalyzed by:
eg: -
Modification of -SH Gropus
Reaction catalyzed by: heavy metal salts
eg: bismuth salicylate active ingredient in Pepto-Bismol -
Lethal Damage to DNA:
expose to:
causes: -
Lethal Damage to DNA:
expose to: electroagnetic radiation
causes: causes irreversible damage to DNA (ss and ds breaks, UV also causes thymine dimers) -
Lethal Damage to DNA
Electromagnetic Radiation
3 types and uses: -
Lethal Damage to DNA
Electromagnetic Radiation
3 types:
1) Ultraviolet irradiation (germicidal lams to clean rooms (air and surfaces))
2) X rays (sterilize food products)
3) Cobalt 60 (gamma rays) (sterilize disposable plastic products) -
Miscellaneous Sterilization Methods (3)
All are: -
Miscellaneous Sterilization Methods (3)
All are: Alkylating agents
1) Formaldehyde gas
2) Glutaldehyde
3) Ethylene oxide - mutagenic