1
Microbial Control
2
Basic Principles of
Microbial Control
3
The Selection of Microbial Control Methods
• Factors Affecting the Efficacy of
Antimicrobial Methods
▫ Site to be treated
 Harsh chemicals and extreme heat cannot be used on
humans, animals, and fragile objects
 Method of microbial control based on site of medical
procedure
4
Relative susceptibilities of microbes to antimicrobial agents
Figure 9.2
5
The Selection of Microbial Control Methods
• Factors Affecting the Efficacy of
Antimicrobial Methods
▫ Relative susceptibility of microorganisms
 Germicides classified as high, intermediate, or low
effectiveness
 High-level kill all pathogens, including endospores
 Intermediate-level kill fungal spores, protozoan cysts,
viruses, and pathogenic bacteria
 Low-level kill vegetative bacteria, fungi, protozoa, and
some viruses
6
Effect of temperature on the efficacy of an
antimicrobial chemical
Figure 9.3
7
The Selection of Microbial Control Methods
• Methods for Evaluating Disinfectants and
Antiseptics
▫ Phenol coefficient
 Evaluates efficacy of disinfectants and antiseptics by
comparing an agent’s ability to control microbes to
phenol
 Greater than 1.0 indicates agent is more effective
than phenol
 Has been replaced by newer methods
8
The Selection of Microbial Control Methods
• Methods for Evaluating Disinfectants and Antiseptics
– Use-dilution test
• Metal cylinders dipped into broth cultures of bacteria
• Contaminated cylinder immersed into dilution of
disinfectant
• Cylinders removed and placed into tube of medium to see
how much bacteria survived
• Most effective agents entirely prevent growth at highest
dilution
• Current standard test in the U.S.
• New standard procedure being developed
9
The Selection of Microbial Control Methods
• Methods for Evaluating Disinfectants and
Antiseptics
▫ Kelsey-Sykes capacity test
 Alternative assessment approved by the
European Union
 Bacterial suspensions added to the chemical
being tested
 Samples removed at predetermined times and
incubated
 Lack of bacterial reproduction reveals minimum
time required for the disinfectant to be effective
10
The Selection of Microbial Control Methods
• Methods for Evaluating Disinfectants and
Antiseptics
▫ In-use test
 Swabs taken from objects before and after
application of disinfectant or antiseptic
 Swabs inoculated into growth medium and
incubated
 Medium monitored for growth
 Accurate determination of proper strength and
application procedure for each specific situation
11
Physical Methods of Microbial Control
• Heat-Related Methods
▫ Effects of high temperatures
 Denature proteins
 Interfere with integrity of cytoplasmic membrane
and cell wall
 Disrupt structure and function of nucleic acids
▫ Thermal death point
 Lowest temperature that kills all cells in broth in 10
min
▫ Thermal death time
 Time to sterilize volume of liquid at set temperature
12
Physical Methods of Microbial Control
• Heat-Related Methods
▫ Moist heat
 Used to disinfect (kill organisms and remove spores),
sanitize (kill organisms but not necessarily their spores),
and sterilize (kill all organisms and spores)
 Denatures proteins and destroys cytoplasmic membranes
 More effective than dry heat
 Methods of microbial control using moist heat




Boiling
Autoclaving
Pasteurization
Ultrahigh-temperature sterilization
13
Physical Methods of Microbial Control
• Heat-Related Methods
▫ Moist heat
 Boiling
 Kills vegetative cells of bacteria and fungi, protozoan
trophozoites, and most viruses
 Boiling time is critical
▫ Different elevations require different boiling times
 Endospores, protozoan cysts, and some viruses can
survive boiling
14
Physical Methods of Microbial Control
• Heat-Related Methods
▫ Moist heat
 Autoclaving
 Pressure applied to boiling water prevents steam from
escaping
 Boiling temperature increases as pressure increases
 Autoclave conditions – 121ºC, 15 psi, 15 min
15
The relationship between temperature and pressure
Figure 9.5
16
Sterility indicator
Figure 9.7
17
Physical Methods of Microbial Control
• Heat-Related Methods
▫ Moist heat
 Pasteurization
 Used for milk, ice cream, yogurt, and fruit juices
 Not sterilization
▫ Heat-tolerant microbes survive
 Pasteurization of milk
▫ Batch method
▫ Flash pasteurization (High temp, short time)
▫ Ultrahigh-temperature pasteurization (very high temp,
very short time)
18
Pasteurization of milk
Batch method
• The batch method uses a vat pasteurizer which consists
of a jacketed vat surrounded by either circulating water,
steam or heating coils of water or steam.
In the vat the milk is heated and
held throughout the holding period
while being agitated. The milk may
be cooled in the vat or removed hot
after the holding time is completed
for every particle.
19
Pasteurization of milk
Flash method
• High Temperature Short Time (HTST)
• Milk is heated to 72°C (161.6°F) for at least 15 seconds.
• Used for perishable beverages like fruit and vegetable
juices, beer, and some dairy products. Compared to
other pasteurization processes, it maintains color and
flavor better.
• It is done prior to filling into containers in order to kill
spoilage microorganisms, to make the products safer and
extend their shelf life. Flash pasteurization must be used
in conjunction with sterile fill technology.
20
Pasteurization of milk
Ultrahigh-temperature method
• Heating for 1-2 seconds at a temperature exceeding
135°C (275°F), which is the temperature required to kill
spores in milk.
• The most common UHT product is milk, but the process
is also used for fruit juices, cream, soy milk, yogurt,
wine, soups, and stews.
• Can cause browning and change the taste and smell of
dairy products.
• UHT canned milk has a typical shelf life of six to nine
months, until opened.
21
Physical Methods of Microbial Control
• Heat-Related Methods
▫ Moist heat
 Ultrahigh-temperature sterilization
 140ºC for 1 sec, then rapid cooling
 Treated liquids can be stored at room temperature
22
Physical Methods of Microbial Control
• Heat-Related Methods
▫ Dry heat
 Used for materials that cannot be sterilized with
moist heat
 Denatures proteins and oxidizes metabolic and
structural chemicals
 Requires higher temperatures for longer time than
moist heat
 Incineration is ultimate means of sterilization
23
Physical Methods of Microbial Control
• Refrigeration and Freezing
▫ Decrease microbial metabolism, growth, and
reproduction
 Chemical reactions occur slower at low temperatures
 Liquid water not available
▫ Psychrophilic microbes can multiply in
refrigerated foods
▫ Refrigeration halts growth of most pathogens
▫ Slow freezing more effective than quick freezing
▫ Organisms vary in susceptibility to freezing
24
Physical Methods of Microbial Control
• Dessication and Lyophilization
▫ Dessication is drying (98% of the water is
removed) inhibits growth due to removal of water
▫ Lyophilization (freeze-drying)
 Substance is rapidly frozen and sealed in a vacuum
 Substance may also be turned into a powder
▫ Used for long-term preservation of microbial
cultures
 Prevents formation of damaging ice crystals
25
The use of dessication as a means of preserving
apricots
Figure 9.8
26
Filtration equipment used for microbial control
Figure 9.9
27
The role of HEPA filters in biological safety cabinets
High-Efficiency Particulate
Arresting (HEPA) air filters are
used in medical facilities,
automobiles, aircraft, and
homes. The filter must remove
99.97% of all particles greater
than 0.3 micrometer from the
air that passes through.
Figure 9.10
28
Physical Methods of Microbial Control
• Osmotic Pressure
▫ High concentrations of salt or sugar in foods to
inhibit growth
▫ Cells in hypertonic solution of salt or sugar lose
water
▫ Fungi have greater ability than bacteria to survive
hypertonic environments
29
Physical Methods of Microbial Control
• Radiation
▫ Ionizing radiation
 Wavelengths shorter than 1 nm
 Electron beams, gamma rays
 Ejects electrons from atoms to create ions
 Ions disrupt hydrogen bonding, cause oxidation, and
create hydroxide ions
 Hydroxide ions denature other molecules (DNA)
 Electron beams – effective at killing but do not
penetrate well
 Gamma rays – penetrate well but require hours to kill
microbes
30
Increased shelf life of food achieved by ionizing
radiation
Figure 9.11
31
32
Physical Methods of Microbial Control
• Radiation
▫ Nonionizing radiation
 Wavelengths greater than 1 nm
 Excites electrons, causing them to make new covalent
bonds
 Affects 3-D structure of proteins and nucleic acids
 UV light causes pyrimidine dimers in DNA
 UV light does not penetrate well
 Suitable for disinfecting air, transparent fluids, and
surfaces of objects
33
Physical Methods of Microbial Control
• Biosafety Levels
▫ Four levels of safety in labs dealing with
pathogens
 Biosafety Level 1 (BSL-1)
 Handling pathogens that do not cause disease in
healthy humans
 Biosafety Level 2 (BSL-2)
 Handling of moderately hazardous agents
 Biosafety Level 3 (BSL-3)
 Handling of microbes in safety cabinets
 Biosafety Level 4 (BSL-4)
 Handling of microbes that cause severe or fatal disease
34
A BSL-4 worker carries
Ebola virus cultures
Figure 9.12
35
Chemical Methods of Microbial Control
• Affect microbes’ cell walls, cytoplasmic
membranes, proteins, or DNA
• Effect varies with differing environmental
conditions
• Often more effective against enveloped viruses
and vegetative cells of bacteria, fungi, and
protozoa
36
Chemical Methods of Microbial Control
• Phenol and Phenolics
▫
▫
▫
▫
▫
Intermediate- to low-level disinfectants
Denature proteins and disrupt cell membranes
Effective in presence of organic matter
Remain active for prolonged time
Commonly used in health care settings, labs, and
homes
▫ Have disagreeable odor and possible side effects
37
Chemical Methods of Microbial Control
• Alcohols
▫ Intermediate-level disinfectants
▫ Denature proteins and disrupt cytoplasmic
membranes
▫ More effective than soap in removing bacteria
from hands
▫ Swabbing of skin with 70% ethanol prior to
injection
38
Chemical Methods of Microbial Control
• Halogens
▫ Intermediate-level antimicrobial chemicals
▫ Believed to damage enzymes via oxidation or by
denaturation
▫ Widely used in numerous applications
 Iodine tablets, iodophores, chlorine treatment,
bleach, chloramines, and bromine disinfection
39
Pre-op preparation for hand surgery
Figure 9.14
40
41
Chemical Methods of Microbial Control
• Oxidizing Agents
▫
▫
▫
▫
Peroxides, ozone, and peracetic acid
Kill by oxidation of microbial enzymes
High-level disinfectants and antiseptics
Hydrogen peroxide (H2O2) can disinfect and
sterilize surfaces
 Not useful for treating open wounds due to catalase
activity: the tissues convert it into H20 and 0ygen
bubbles.
▫ Ozone treatment of drinking water
▫ Peracetic acid is an effective sporocide used to
sterilize equipment
42
Chemical Methods of Microbial Control
• Surfactants
▫ “Surface active” chemicals
 Reduce surface tension of solvents
▫ Soaps and detergents
 Soaps have hydrophilic and hydrophobic ends
 Good degerming agents but not antimicrobial
 Detergents are positively charged organic surfactants
▫ Quats (Quaternary ammonium cations)
 Low-level disinfectants; disrupts cell membranes
 Ideal for many medical and industrial applications
 Good against fungi, amoeba, and enveloped viruses,
but not endospores, Mycobacterium tuberculosis and
non-enveloped viruses.
43
Chemical Methods of Microbial Control
• Heavy Metals
▫ Heavy-metal ions denature proteins
▫ Low-level bacteriostatic and fungistatic agents
▫ 1% silver nitrate to prevent blindness caused by N.
gonorrhoeae
▫ Thimerosal used to preserve vaccines
▫ Copper inhibits algal growth
44
Chemical Methods of Microbial Control
• Aldehydes
▫ Compounds containing terminal –CHO groups
▫ Cross-link functional groups to denature proteins
and inactivate nucleic acids
▫ Glutaraldehyde disinfects and sterilizes
▫ Formalin used in embalming and disinfection of
rooms and instruments
45
Chemical Methods of Microbial Control
• Gaseous Agents
▫ Microbicidal and sporicidal gases used in closed
chambers to sterilize items
▫ Denature proteins and DNA by cross-linking
functional groups
▫ Used in hospitals and dental offices
▫ Disadvantages




Can be hazardous to people
Often highly explosive
Extremely poisonous
Potentially carcinogenic
46
Chemical Methods of Microbial Control
• Enzymes
▫ Antimicrobial enzymes act against microorganisms
▫ Human tears contain lysozyme
 Digests peptidoglycan cell wall of bacteria
▫ Enzymes to control microbes in the environment
 Lysozyme used to reduce the number of bacteria in
cheese
 Prionzyme can remove prions on medical
instruments
47
Chemical Methods of Microbial Control
• Antimicrobials
▫ Antibiotics, semi-synthetic, and synthetic
chemicals
▫ Typically used for treatment of disease
▫ Some used for antimicrobial control outside the
body
48
Chemical Methods of Microbial Control
• Development of Resistant Microbes
▫ Little evidence that products containing antiseptic
and disinfecting chemicals is beneficial to human
or animal health
▫ Use of such products promotes development of
resistant microbes
49
Antimicrobial Agents
• Chemicals that affect physiology in any manner
• Chemotherapeutic agents
▫ Drugs that act against diseases
• Antimicrobial agents
▫ Drugs that treat infections
50
The History of Antimicrobial Agents
• Semi-synthetics
▫ Chemically altered antibiotics that are more
effective than naturally occurring ones
• Synthetics
▫ Antimicrobials that are completely synthesized in
a lab
51
Mechanisms of Antimicrobial Action
• Key is selective toxicity
• Antibacterial drugs constitute largest number
and diversity of antimicrobial agents
• Fewer drugs to treat eukaryotic infections
(protozoa, fungi, helminthes)
• Even fewer antiviral drugs
52
Mechanisms of Antimicrobial
Action
•
•
•
•
•
•
Inhibition of bacterial wall synthesis
Disruption of existing cytoplasmic membranes
Inhibition of Protein Synthesis
Inhibition of Nucleic Acid Synthesis
Inhibition of Metabolic Pathways
Prevention of Virus Attachment
53
Basic Principles of Microbial Control
• Action of Antimicrobial Agents
▫ Alteration of cell walls and membranes
 Cell wall maintains integrity of cell
 Cells burst due to osmotic effects when damaged
 Cytoplasmic membrane controls passage of
chemicals into and out of cell
 Cellular contents leak out when damaged
 Non-enveloped viruses have greater tolerance of
harsh conditions
54
Mechanisms of Antimicrobial Action
• Inhibition of Cell Wall Synthesis
▫ Inhibition of bacterial wall synthesis
 Most common agents prevent cross-linkage of NAMNAG subunits
 Beta-lactams are most prominent in this group
 Functional groups are beta-lactam rings
 Beta-lactams bind to enzymes that cross-link NAMNAG subunits
 Bacteria have weakened cell walls and eventually lyse
55
Mechanisms of Antimicrobial Action
• Inhibition of Cell Wall Synthesis
▫ Inhibition of synthesis of bacterial walls
 Semi-synthetic derivatives of beta-lactams




More stable in acidic environments
More readily absorbed
Less susceptible to deactivation
More active against more types of bacteria
 Simplest beta-lactams – effective only against
aerobic Gram-negatives
56
Mechanisms of Antimicrobial Action
• Inhibition of Cell Wall Synthesis
▫ Inhibition of synthesis of bacterial walls
 Vancomycin and cycloserine
 Interfere with particular bridges that link NAM
subunits in many Gram-positives
 Bacitracin
 Blocks secretion of NAG and NAM from cytoplasm
 Effective against Gram positives
 Isoniazid and ethambutol
 Disrupt mycolic acid formation in mycobacterial
species
57
Mechanisms of Antimicrobial Action
• Inhibition of Cell Wall Synthesis
▫ Inhibition of synthesis of bacterial walls
 Prevent bacteria from increasing amount of
peptidoglycan
 Have no effect on existing peptidoglycan layer
 Effective only for growing cells
58
Mechanisms of Antimicrobial Action
• Disruption of Cytoplasmic Membranes
▫ Some drugs form channels through cytoplasmic
membrane and damage its integrity
▫ Amphotericin B attaches to ergosterol in fungal
membranes
 Humans somewhat susceptible because cholesterol
similar to ergosterol
 Bacteria lack sterols; not susceptible
59
Mechanisms of Antimicrobial Action
• Disruption of Cytoplasmic Membranes
▫ Azoles and allyamines inhibit ergosterol synthesis
▫ Polymyxin disrupts cytoplasmic membranes of
Gram-negatives
 Oral form is toxic to human kidneys, so only used
topically
▫ Some parasitic drugs act against cytoplasmic
membranes
60
Which topical ointment is best?
• Neomycin is an aminoglycoside antibiotic (disrupts protein synthesis). It
has excellent activity against Gram-negative bacteria, and has
partial activity against Gram-positive bacteria.
• Polymixin disrupts bacterial cell membranes by interacting with its
phospholipids. They are selectively toxic for Gram-negative bacteria.
• Bacitracin disrupts cell wall synthesis. Its action is on Gram-positive
organisms. It can cause contact dermatitis and cross-reacts with allergic
sensitivity to sulfa-drugs.
• Which topical ointment is best: Neomycin or Triple Antibiotic (contains all
three)
61
Basic Principles of Microbial Control
• Action of Antimicrobial Agents
▫ Damage to proteins and nucleic acids
 Protein function depends on 3-D shape
 Extreme heat or certain chemicals denature proteins
 Chemicals, radiation, and heat can alter or destroy
nucleic acids
 Can produce fatal mutants
 Can halt protein synthesis through action on RNA
62
Mechanisms of Antimicrobial Action
• Inhibition of Protein Synthesis
▫
▫
▫
▫
Prokaryotic ribosomes are 70S (30S and 50S)
Eukaryotic ribosomes are 80S (40S and 60S)
Drugs can selectively target translation
Mitochondria of animals and humans contain 70S
ribosomes
 Can be harmful
63
Mechanisms of Antimicrobial Action
• Inhibition of Protein Synthesis
▫ Aminoglycosides: excellent against Gram negatives,
partially effective against Gram positives






amikacin (Amikin®)
gentamicin (Garamycin®)
kanamycin (Kantrex®)
neomycin (Mycifradin®)
streptomycin
tobramycin (TOBI Solution®, TobraDex®)
64
Antimicrobial inhibition of protein
synthesis
Figure 10.4
65
Mechanisms of Antimicrobial Action
• Inhibition of Nucleic Acid Synthesis
▫ Several drugs block DNA replication or mRNA
transcription
▫ Drugs often affect both eukaryotic and prokaryotic
cells
▫ Not normally used to treat infections
▫ Used in research and perhaps to slow cancer cell
replication
66
Nucleotides
Nucleotides and some
of their antimicrobial
analogs
Figure 10.7
67
Acyclovir
• Acyclovir is used to decrease pain and speed the healing of herpes sores or
blisters in people who have varicella (chickenpox), herpes zoster (shingles;
a rash that can occur in people who have had chickenpox in the past), and
first-time or repeat outbreaks of genital herpes (a herpes virus infection
that causes sores to form around the genitals and rectum from time to
time).
• Acyclovir is also sometimes used to prevent outbreaks of herpes sores in
people who are infected with the virus.
• Acyclovir disrupts nucleic acid function. It works by stopping the spread of
the herpes virus in the body. Acyclovir will not cure herpes or protect others
from catching it.
68
Mechanisms of Antimicrobial Action
• Inhibition of Nucleic Acid Synthesis
▫ Quinolones and fluoroquinolones
 Act against prokaryotic DNA gyrase (enzyme that is
needed for DNA to unwind during replication)
▫ Inhibitors of RNA polymerase (enzyme used
during transcription)
▫ Reverse transcriptase inhibitors
 Act against an enzyme HIV uses in its replication
cycle
 Does not harm people because humans lack reverse
transcriptase
69
Mechanisms of Antimicrobial Action
• Inhibition of Nucleic Acid Synthesis
▫ Nucleotide analogs
 Interfere with function of nucleic acids
 Distort shapes of nucleic acid molecules and prevent
further replication, transcription, or translation
 Most often used against viruses
 Effective against rapidly dividing cancer cells
70
Nucleotides
Nucleotides and some
of their antimicrobial
analogs
Figure 10.7
71
Mechanisms of Antimicrobial Action
• Inhibition of Metabolic Pathways
▫ Antimetabolic agents can be effective when
pathogen and host metabolic processes differ
▫ Quinolones interfere with the metabolism of
malaria parasites
▫ Heavy metals inactivate enzymes
▫ Some agents disrupt glucose uptake by many
protozoa and parasitic worms
▫ Some drugs block activation of viruses
72
Mechanisms of Antimicrobial Action
• Inhibition of Metabolic Pathways
▫ Antiviral agents can target unique aspects of viral
metabolism
 Amantadine, rimantadine, and weak organic bases
prevent viral uncoating
▫ Protease inhibitors interfere with an enzyme that
HIV needs in its replication cycle
73
Mechanisms of Antimicrobial Action
• Prevention of Virus Attachment
▫ Attachment antagonists block viral attachment or
receptor proteins
▫ New area of antimicrobial drug development
74
Clinical Considerations in Prescribing
Antimicrobial Drugs
• Ideal Antimicrobial Agent
▫ Readily available
▫ Inexpensive
▫ Fast-acting
▫
▫
▫
▫
▫
Chemically stable during storage
Easily administered
Nontoxic and nonallergenic
Selectively toxic against wide range of pathogens
Capable of controlling microbial growth while being harmless
to humans, animals, and objects
75
Clinical Considerations in Prescribing
Antimicrobial Drugs
• Spectrum of Action
▫ Number of different pathogens a drug acts against
 Narrow-spectrum effective against few organisms
(Gram positive bacteria only)
 Broad-spectrum effective against many organisms
(Gram positive and Gram negative bacteria)
 May allow for secondary or superinfections to develop
 Killing of normal flora reduces microbial antagonism
76
Spectrum of action for selected
antimicrobial agents
Figure 10.8
77
Clinical Considerations in Prescribing
Antimicrobial Drugs
• Efficacy
▫ Ascertained by
 Diffusion susceptibility test
 Minimum inhibitory concentration test
 Minimum bactericidal concentration test
78
Diffusion Susceptibility Test:
Zone of inhibition
Figure 10.9
79
Minimum inhibitory concentration test
Figure 10.10
80
A minimum bactericidal concentration
test
Figure 10.12
81
Clinical Considerations in Prescribing
Antimicrobial Drugs
• Routes of Administration
▫ Topical application of drug for external infections
▫ Oral route requires no needles and is selfadministered
▫ Intramuscular (IM) administration delivers drug
via needle into muscle
▫ Intravenous (IV) administration delivers drug
directly to bloodstream
▫ Must know how antimicrobial agent will be
distributed to infected tissues
82
Effect of route of
administration on
chemotherapeutic
agent
Figure 10.13
83
Clinical Considerations in Prescribing
Antimicrobial Drugs
• Safety and Side Effects
▫ Toxicity
 Cause of many adverse reactions poorly understood
 Drugs may be toxic to kidneys, liver, or nerves
 Consideration needed when prescribing drugs to
pregnant women
▫ Allergies
 Allergic reactions are rare but may be life
threatening
 Anaphylactic shock
84
Side effects resulting from toxicity of
antimicrobial agents
Figure 10.14
85
Clinical Considerations in Prescribing
Antimicrobial Drugs
• Safety and Side Effects
▫ Disruption of normal microbiota
 May result in secondary infections
 Overgrowth of normal flora causing superinfections
 Of greatest concern for hospitalized patients
86
Resistance to Antimicrobial Drugs
• The Development of Resistance in
Populations
▫ Some pathogens are naturally resistant
▫ Resistance by bacteria acquired in two ways
 New mutations of chromosomal genes
 Acquisition of resistance genes (R-plasmids) via
transformation, transduction, and conjugation
87
The development of a resistant strain
of bacteria
Figure 10.15
88
Resistance to Antimicrobial Drugs
• Mechanisms of Resistance
▫ At least six mechanisms of microbial resistance
 Production of enzyme that destroys or deactivates
drug
 Slow or prevent entry of drug into the cell
 Alter target of drug so it binds less effectively
 Alter their metabolic chemistry
 Pump antimicrobial drug out of the cell before it can
act
 Mycobacterium tuberculosis produces MfpA protein
 Binds DNA gyrase preventing the binding of
fluoroquinolone drugs
89
How -lactamase renders penicillin
inactive
Figure 10.16
90
Resistance to Antimicrobial Drugs
• Multiple Resistance and Cross Resistance
▫ Pathogen can acquire resistance to more than one
drug
▫ Common when R-plasmids exchanged
▫ Develop in hospitals and nursing homes
 Constant use of drugs eliminates sensitive cells
▫ Superbugs
▫ Cross resistance
91
Resistance to Antimicrobial Drugs
• Retarding Resistance
▫ Maintain high concentration of drug in patient for
sufficient time
 Kills all sensitive cells and inhibits others so immune
system can destroy
▫ Use antimicrobial agents in combination
 Synergism vs. antagonism
92
Example of synergism between two
antimicrobial agents
Figure 10.17
93
Resistance to Antimicrobial Drugs
• Retarding Resistance
▫ Use antimicrobials only when necessary
▫ Develop new variations of existing drugs
 Second-generation drugs
 Third-generation drugs
▫ Search for new antibiotics, semi-synthetics, and
synthetics
 Bacteriocins
 Design drugs complementary to the shape of
microbial proteins to inhibit them
94
Vaccination
• Vaccine – use the immune system to protect
against infectious disease
• Types of vaccines
▫ attenuated (weakened) microbe; virulence factors are
removed
▫ heat-killed / chemically killed microbe
▫ toxoids
• Passive versus Adaptive vaccination
▫ passive – immune system products from another
 mothers milk (presence of IgA)
 gamma-globulin (anti-bee venom, anti-hepatitis A, etc)
▫ active – stimulate individuals immune system to produce
memory cells
95
Effect of smallpox vaccine
Initial “modern” vaccine: 1796.
96
U.S. cases
against
diseases for
which there
are vaccines.
SSPE: sub-acute sclerosing
panencephalitis (late stage
measles)
97
• Why Your Cellphone Has More Bacteria
Than a Toilet Seat
• By Susan E. Matthews, MyHealthNewsDaily
Staff Writer | LiveScience.com – 3 hrs ago
• http://news.yahoo.com/why-cellphone-morebacteria-toilet-seat-124147769.html
98
• Cellphones carry 10 times more bacteria than
most toilet seats, so it shouldn't be surprising
that a man in Uganda reportedly contracted
Ebola after stealing one.
• He stole the phone from a quarantined ward of a
hospital, near the site of a recent Ebola outbreak.
• While toilets tend to get cleaned frequently,
because people associate the bathroom with
germs, cellphones and other commonly handled
objects — like remote controls— are often left
out of the cleaning routine.
• Cellphones pick up germs all the time; some
people talk on their phone on toilets.
99
• However, the amount of germs on a phone isn't a
problem — it’s the sharing of phones between
people. Without sharing, each phone carries just
one set of germs, and won't get its owner sick.
• The problem with phones is that we're in
constant contact with them, and they spend a lot
of time in close proximity to our faces and
mouths.
• And, because it's an electronic device, most
people are hesitant about cleaning them.
100
• This is also this case with remote controls,
which, are also often used by people when
they're sick.
• Remotes are more frequently shared, too, so
they're usually even worse than phones for
spreading germs.
• Other common culprits that are hotspots of
unseen disease include office phones, shopping
carts and the first-floor buttons of elevators.
101