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Microbiology Exam Study Guide

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1. Approaches to Control Microbes a. Physical Methods i. Dry 1. incineration or dry oven  sterilization ii. Moist heat 1. Boiling water, steam under pressure  sterilization 2. Kills microbes by denaturing enzymes 3. Ex. Autoclaving iii. Radiation 1. Irradiation – bombardment wit...

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  • January 27, 2021
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Microbiology Exam 2 Study Guide

Chapter 11 – Controlling Microbes
1. Approaches to Control Microbes
a. Physical Methods
i. Dry
1. incineration or dry oven  sterilization
ii. Moist heat
1. Boiling water, steam under pressure  sterilization
2. Kills microbes by denaturing enzymes
3. Ex. Autoclaving
iii. Radiation
1. Irradiation – bombardment with radiation
2. Ionizing – can penetrate a solid barrier, bombard a cell, enter it,
and dislodge electrons form molecules
a. x-ray, cathode, gamma  sterilization
3. Nonionizing – enters a cell, strike molecules, and excites them.
Results? Mutation of DNA
a. Note: non-ionizing radiation cannot penetrate a solid
barrier
b. UV  disinfection
iv. Chemical Methods
1. Antimicrobial chemicals  disinfection or sterilization
2. Gases  disinfection of sterilization
v. Mechanical Methods
1. Filtration of air and liquids  decontamination

2. Physical Controls
a. Heat
i. Moist heat – boiling water (100oC, 30 min)
ii. Pasteurization – milk, fruit juices; flash method (~72oC, 15 sec)
iii. Pressurized steam – autoclave (121oC, 15psi); used for surgical
instruments, commercial canning (clostridium botulinum, problem in
canning)
b. Radiation
i. Gamma radiation – DNA
1. Medical equipment, drugs, food-safe
ii. Ultraviolet radiation – DNA
iii. Microwave – heat

, 3. Factors in Treatment
a. Situation – home, hospital, lab, factory
i. Sepsis – the growth of microorganisms in the blood & other tissue
b. Surface or medium
c. Type and number of microorganisms
i. Highest resistance = endospores
ii. Moderate resistance = mycobacterium, S. aureus
iii. Least resistance = non-endospore formers
d. Environment
e. Concentration of agent being used
f. Mode of action

4. Mechanical Controls
a. 2 kinds
i. Fluid filtration
ii. Air filtration – HEPA; hospitals
b. Decontaminating Congress – letters containing Bacillus anthracis were opened in
Hart Office of US Senate in 2001
i. B. anthracis is spore-forming – eradication is tough; building was heavily
populated, needed to decontaminate heating/AC vents, carpet, furniture,
office equipment, sensitive papers, artwork, personal belongings
c. Decontamination Process
i. Size/scope – samples taken from 25 buildings
ii. Decontamination – vacuum with HEPA filter followed by tx with liquid
chlorine dioxide (sterilant used for treatment of medical waste) or a
decontamination foam; heavily contaminated areas used gaseous ClO 2

5. Chemical Controls
a. Factors for choosing appropriate germicide: storage/stability, residue,
cost/availability, environmental risk
b. Germicidal Chemical:
i. Alcohols, hydrogen peroxide (H2O2), ethylene oxide (used on medical
instruments, plastics; sugar, spices)

6. –static? or –cidal?
a. Bactericide – a chemical that destroys bacteria except for those in the endospore
stage
b. Germicide/Microbicide – chemical agents that kill microorganisms
c. Bacteristatic – prevent the growth of bacteria on tissues or on objects in the
environment
d. Fungistatic – inhibit fungal growth
e. Microbistatic – antiseptics & drugs (used in the body)
f. Degermination – reducing the number of microbes on the skin (ex. hand
sanitizers)

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