Download Chapter 7 Control of Microbial Growth

Chapter 7
Control of Microbial Growth
• Boiling kills microbes by coagulating the
proteins – endospores are not destroyed.
• Autoclaving - Temperature 121oC, 15 PSI,
15 min – even the endospores are
destroyed.
• Dry heat – direct flaming is used to
sterilize the inoculating loop.
• Refrigeration – slows down the growth of
microbes. It does not kill the microbes.
• Osmotic environment – high concentration
of salt – plasmolysis.
• UV light – mutation – inducing the
formation of thymine dimers.
• Iodine - inactivates enzymes – skin
infection, wound infection.
• 1% silver nitrate – ophthalmea
neonatorum – eye infection of the
newborn.
• Gas sterilization – ethylene oxide –
mattresses, petri plates.
• Quaternary ammonium compounds –
damage to the plasma membrane –
mouthwash.
• Sodium nitrite – preserve meat products –
prevents the germination of botulism
endospores – used to preserve hot dogs.
The Terminology of Microbial
Control
• Sepsis refers to microbial contamination
• Asepsis is the absence of significant
contamination
• Aseptic surgery techniques prevent
microbial contamination of wounds
The Terminology of Microbial
Control
• Sterilization: Removing all microbial life
• Commercial sterilization: Killing C.
botulinum endospores
• Disinfection: Removing pathogens
• Antisepsis: Removing pathogens from
living tissue
The Terminology of Microbial
Control
• Degerming: Removing microbes from a
limited area
• Sanitization: Lowering microbial counts on
eating utensils
• Biocide/germicide: Kills microbes
• Bacteriostasis: Inhibiting, not killing,
microbes
• The usual definition of sterilization is the
removal or destruction of all forms of
microbial life;
Effectiveness of Treatment
• Depends on
– Number of microbes
– Environment (organic matter, temperature,
biofilms)
– Time of exposure
– Microbial characteristics
Actions of Microbial Control
Agents
• Alteration of membrane permeability
• Damage to proteins
• Damage to nucleic acids
Moist Heat Sterilization
• Moist heat denatures proteins
• Autoclave: Steam under pressure
An Autoclave
Figure 7.2
Pasteurization
• Reduces spoilage organisms and
pathogens
• Equivalent treatments
– 63°C for 30 min
Dry Heat Sterilization
• Kills by oxidation
– Dry heat
– Flaming
– Incineration
– Hot-air sterilization
Equivalent Treatments
Hot-Air
Autoclave
170˚C, 2 hr
121˚C, 15 min
Filtration
• Membrane
filtration
removes
microbes
>0.22 µm
Figure 7.4
Physical Methods of Microbial
Control
• Low temperature inhibits microbial growth
– Refrigeration
– Deep-freezing
– Lyophilization
• High pressure denatures proteins
• Desiccation prevents metabolism
• Osmotic pressure causes plasmolysis
Radiation
Figure 7.5
Principles of Effective
Disinfection
•
•
•
•
Concentration of disinfectant
Organic matter
pH
Time
Bisphenols
• Hexacholorphene, triclosan
– Disrupt plasma membranes
Figure 7.7c, d
Biguanides
• Chlorhexidine
– Disrupt plasma membranes
Halogens
• Iodine
– Tinctures: In aqueous alcohol
– Iodophors: In organic molecules
– Alter protein synthesis and membranes
• Chlorine
– Bleach: Hypochlorous acid (HOCl)
– Chloramine: Chlorine + ammonia
– Oxidizing agents
Heavy Metals
• Ag, Hg, and Cu
– Silver nitrate may be used to prevent
gonorrheal ophthalmia neonatorum
– Silver sulfadiazine used as a topical cream on
burns
– Copper sulfate is an algicide
• Oligodynamic action
– Denature proteins
Chemical Food Preservatives
• Organic acids
– Inhibit metabolism
– Sorbic acid, benzoic acid, and calcium
propionate
– Control molds and bacteria in foods and
cosmetics
• Nitrite prevents endospore germination
• Antibiotics
– Nisin prevent spoilage of cheese
Gaseous Sterilants
• Denature proteins
• Use: Heat-sensitive material
– Ethylene oxide
Chapter 18
Practical Applications of
Immunology
History of Vaccines
• Variolation: Inoculation of smallpox into skin
(18th century)
• Vaccination:
– Inoculation of cowpox virus into skin (Jenner) 1790
Types of Vaccines
• Attenuated whole-agent vaccines
– MMR
• Inactivated whole-agent vaccines
 Salk polio
• Toxoids
– Tetanus
Types of Vaccines
• Subunit vaccines
– Acellular pertussis
– Recombinant hepatitis B
• Nucleic acid (DNA) vaccines
– West Nile (for horses)
– DNA injected into skin cells, protein made –
stimulates immune system.
The Development of New
Vaccines
• Culture pathogen
• rDNA techniques
– In plants
• Adjuvants
• Deliver in combination
Diagnostic Immunology
• Sensitivity: Probability that the test is
reactive if the specimen is a true positive
• Specificity: Probability that a positive
test will not be reactive if a specimen is a
true negative
Monoclonal Antibodies (Mabs)
• Hybridoma: “Immortal” cancerous B cell
fused with an antibody-producing normal B
cell, produces
• Monoclonal antibodies
Monoclonal Antibodies
Figure 18.2
Monoclonal Antibodies
Figure 18.2
Monoclonal Antibodies
Figure 18.2
Monoclonal Antibodies (Mabs)
• Infliximab: For Crohn’s disease, blocks
cytokine
• Ibritumomab + rituximab: For nonHodgkin’s lymphoma, destroy cancer cells
• Trastuzumab: Herceptin for breast cancer
• Spread of cancer
Agglutination Reactions
• Particulate
antigens and
antibodies
• Antigens on a
cell (direct
agglutination)
Figure 18.5
Indirect Agglutination
Figure 18.7
Complement Fixation Test
Figure 18.10
Complement Fixation Test
Figure 18.10
Fluorescent-Antibody (FA)
Techniques
• Direct FA
Figure 18.11a
Indirect Fluorescent-Antibody
Test
Figure 18.11b
Enzyme-Linked Immunosorbent
Assay
• Also called ELISA
• Enzyme linked to Ab is the indicator
Direct ELISA
Figure 18.14a
Indirect ELISA
Figure 18.14b
Serological Tests
Figure 18.13
Serological Tests
• Direct tests detect antigens (from
patient sample)
• Indirect tests detect antibodies (in
patient’s serum)
ELISA
• Enzyme liked immunosorbent assay
• Plastic plates with wells in them are used
• Direct ELISA – presence of antigen in a
sample
• Indirect ELISA – presence of antibodies
against a specific antigen in a sample.
Neisseria
gonorrhoeae
Antibodies against
HIV
Secondary antibodies
Enzyme linked
antibodies
Substrate – colorless
Product – blue
Against human
Antibodies.