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BIOS 350
CHAPTER 13
CONTROL OF MICROBIAL GROWTH
1
Microbes are Everywhere
â—¦ Fomites: Inanimate
objects that can transmit
disease
2
Biological Safety Levels Matter
3
Important Terms
â—¦ Aseptic Technique: Techniques to maintain sterility or prevent contamination
â—¦ Sepsis: Body wide infection causing systemic inflammation, high fever, increased heart
and respiratory rates, shock, and potentially death
â—¦ Sterilization: Complete removal of all microbes including vegetative cells, endospores,
and viruses,
â—¦ Sterilants: Chemicals that can sterilize if used properly
â—¦ Disinfection: Not sterile, heat or chemicals kill many microbes on fomite surfaces.
â—¦ Antiseptics: Not sterile, chemicals safe to lower microbial counts on living tissues such as skin
and mucus membranes
â—¦ Degerming: Removing microbes from living tissues with the help of scrubbing
â—¦ Sanitization: Cleaning fomites so they are safe for the general public
â—¦ Critical items: Medical equipment that must be sterile
â—¦ Semicritical items: Highly disinfected but not necessarily needing to be sterile
â—¦ Noncritical items: Need to be clean but not highly disinfected
4
Measuring Microbial Control
â—¦ Suffixes Matter
â—¦ -cide means to kill
â—¦ -static means to inhibit growth
â—¦ Microbial Death Curve
â—¦ Tracks decline (death) of population
â—¦ Not all cells die at the same time
â—¦ Decimal Reduction time
â—¦ Time to reduce population ten-fold on a log
scale (90% on an arithmetic scale)
â—¦ Depends on amount of starting population
â—¦ Depends on temperature or concentration
of chemicals
â—¦ Depends on organic matter present
5
Physical Control Methods
Methods:
â—¦ Heat
â—¦ Radiation
â—¦ Filtration
â—¦ Desiccation
How they work:
â—¦ Disrupt membranes
â—¦ Change membrane
permeability
â—¦ Damage proteins and
nucleic acids
â—¦ Remove microbes from
sample
6
Physical Control Methods
â—¦ Heat
â—¦ Alters membranes
â—¦ Denatures proteins
â—¦ Thermal Death Point:
â—¦ Lowest temperature to kill
all microbes within a 10
minute period
â—¦ Thermal Death Time:
â—¦ Amount of time it takes to
kill all microbes at a
particular temperature
â—¦ Dry Heat Sterilization:
â—¦ Burning or incineration
◦ Dry oven 170℃ for at least 2
hours
â—¦ Moist Heat Sterilization:
â—¦ Autoclaves
â—¦ Brings temperature of water to
121℃ to boil using increased
pressure
â—¦ Can kill all vegetative cells,
endospores, and destroy all
viruses
◦ Boiling water at 100℃ does not
kill endospores
7
Physical Control Methods
8
Physical Control Methods
9
Physical Control Methods
â—¦ Pressure:
â—¦ Also called pascalization
â—¦ Used in food industry
â—¦ Does not sterilize
â—¦ Hyperbaric Oxygen Therapy
â—¦ Patient breathes pure oxygen at
higher pressure
â—¦ Usually in hyperbaric chamber
â—¦ Pressurized oxygen breathing
tube
â—¦ Increases oxygen content in blood
â—¦ Increases immune activity
â—¦ Increases ROS which can damage
strict anaerobes causing infection
10
Physical Control Methods
11
Physical Control Methods
Ionizing Radiation
â—¦ Examples:
â—¦ X-rays
â—¦ Gamma rays
â—¦ High energy electron
beams
â—¦ How it works:
â—¦ Damages DNA
â—¦ Ionizes water to make
ROS
â—¦ Uses
Nonionizing Radiation
â—¦ Examples:
â—¦ Microwaves
â—¦ UV light
â—¦ How it works:
â—¦ Microwaves generate heat
â—¦ UV light damages DNA
â—¦ Uses:
â—¦ Water purification
â—¦ Germicidal lamps
â—¦ Biological safety cabinets
â—¦ Sterilize materials that
can’t be autoclaved
â—¦ Sterilize tissues and
drugs
â—¦ Food preservation
12
Physical Control Methods
Sonication
â—¦ High frequency ultrasound waves
â—¦ Disrupts cell structures
â—¦ Cleans surgical instruments, lenses, and
other objects
â—¦ Does not sterilize
Filtration
â—¦ Physically separates microbes from
sample
â—¦ HEPA filters air
â—¦ Membrane filters liquids
â—¦ Can sterilize depending on the sample
13
Chemical Control of Microbes
Phenolics
â—¦ Lister first to use clinical (carbolic acid)
â—¦ Work by denaturing proteins and
disrupting membranes
â—¦ Common examples:
â—¦ Lysol
â—¦ Triclosan
â—¦ pHisoHex
Heavy Metals
â—¦ Used early in history
â—¦ Mercury to treat syphilis
â—¦ Silver nitrate droplets to protect newborn
eyes
â—¦ Copper prevents algae growth
â—¦ Nickel and Zinc also have antimicrobial
properties
â—¦ Work by binding to proteins and
denaturing enzymes
â—¦ Common Examples:
â—¦ Mostly in clinical settings (mercuric chloride
disinfectant)
â—¦ Silver in bandages
â—¦ Zinc oxide in diaper rash cream and
dandruff shampoo
14
Chemical Control of Microbes
Halogens
â—¦ Examples: iodine, chlorine, and fluorine
â—¦ How they work:
â—¦ Iodine and chlorine act as oxidizing agents
and damage organic molecules
â—¦ Fluorine incorporated into tooth enamel to
strengthen it and also can accumulate in
bacteria disrupting their metabolism
â—¦ Common examples:
â—¦ Betadine
â—¦ Bleach
â—¦ Various toothpastes, mouthwash, and
municipal water
Alcohols
â—¦ Examples:
â—¦ 70% isopropyl and 70% ethanol
â—¦ Also form tinctures when combined with
other antimicrobials (iodine)
â—¦ How they work:
â—¦ Denature proteins
â—¦ Disrupt cell membranes
â—¦ Lead to cell lysis
â—¦ Common examples:
â—¦ Alcohol based hand sanitizer
â—¦ Alcohol pads
15
Chemical Control of Microbes
Surfactants
â—¦ Surface Acting Agents
Bisbiguanides
â—¦ Lower surface tension of water
â—¦ Cationic molecules with antiseptic
properties
â—¦ Help remove microbes from surfaces
â—¦ How they work:
â—¦ How they work:
â—¦ Interact with nonpolar areas in oil and
grease to form emulsions
â—¦ Loosen and lift away dirt and microbes
â—¦ QUATS (quaternary ammonium salts)insert
into membrane disrupting it
â—¦ Disrupts cell membrane
â—¦ Causes congealing of cytoplasmic
contents
â—¦ Common examples:
â—¦ Chlorhexidine in surgical soaps, topical
antiseptics, and oral rinses
â—¦ Common examples:
â—¦ Soaps and detergents
â—¦ QUATs added to Lysol
â—¦ QUATs added to skin antiseptics, oral
rinses, and mouthwash
16
Chemical Control of Microbes
Alkylating Agents
Peroxygens
â—¦ Strong disinfectants that can sterilize
â—¦ Strong oxidizing agents
â—¦ How they work:
â—¦ Inactivate enzymes and nucleic acids
â—¦ Cross links proteins
â—¦ Common examples:
â—¦ Formaldehyde: embalming solution
â—¦ Glutaraldehyde: Cidex disinfectant /
sterilizing agent
â—¦ OPA (o- phthalaldehyde) also found in
Cidex and is less irritating to nasal passages
â—¦ Ethylene oxide: sterilization of heat sensitive
items
◦ β-Propionolactone: sterilization agent for
tissue graft and vaccines
â—¦ Can be used as disinfectants,
antiseptics, and in high concentration
as gaseous sterilizing agents
â—¦ How it works:
â—¦ Produces free radicals that damage
organic molecules (ROS)
â—¦ Common examples:
â—¦ Hydrogen peroxide
â—¦ Benzoyl peroxide
â—¦ Carbamide peroxide (toothpaste)
â—¦ Ozone gas (treats water or air)
â—¦ In humans and animals it is metabolized into
lactic acid
â—¦ Can damage eyes and kidneys and is a known
carcinogen
17
Chemical Control of Microbes
Super critical fluids
â—¦ Super critical Carbon Dioxide
â—¦ CO2 brought to pressure 10 x atmosphere
â—¦ Physical properties between liquid and
gas
â—¦ Can penetrate to sterilize while being
nontoxic, nonreactive, and
nonflammable
â—¦ How it works:
â—¦ Penetrates cells and forms carbonic acid
lower cell’s pH
â—¦ Uses:
â—¦ Treat foods
â—¦ Treat tissues before transplant
â—¦ Pest control
Food preservatives
â—¦ Inhibit microbial growth and prevent
spoilage
â—¦ Common examples: sorbic acid,
benzoic acid, propionic acid
â—¦ How they work:
â—¦ Sorbic acid inhibit cellular enzymes
â—¦ Benzoic acid decreases intracellular pH,
interferes with oxidative phosphorylation,
and prevents uptake of certain amino
acids
â—¦ Propionic acid inhibit cellular enzymes
and decrease intracellular pH
18
Testing the Effectiveness of
Antiseptics and Disinfectants
Environmental conditions influence
the potency
â—¦ Length of exposure
â—¦ Concentration of chemical agent
â—¦ Temperature, pH, and amount of
organics present
Phenol Coefficient
◦ Chemical’s effectiveness compared to
phenol
â—¦ Test organisms:
â—¦ Staphylococcus aureus
â—¦ Salmonella enterica serovar Typhi
â—¦ 1= as good as phenol
â—¦ Less than 1 = not as good as phenol
â—¦ Great than 1= better than phenol
â—¦ Not commonly used any more
19
Testing the Effectiveness of
Antiseptics and Disinfectants
20
Testing the Effectiveness of
Antiseptics and Disinfectants
21
BIOS 350
CHAPTER 14
ANTIMICROBIAL DRUGS
1
Ancient Antimicrobial
â—¦ Tetracycline found in
ancient skeletal remains
â—¦ Plants are used medicinally
by many cultures
2
The Magic Bullets
â—¦ Scientists looking for chemicals to harm the pathogens
but not the person
◦ Paul Ehrlich’s compound 606
â—¦ arsenic-containing compounds
â—¦ for treatment of syphilis
â—¦ Gerhard Domagk and others discovered prontosil
â—¦ Breaks down into sulfanilamide in the body
â—¦ Used to treat Streptococcal and Staphylococcal infections
â—¦ Sulfanilamide is a synthetic antimicrobial (not naturally made)
â—¦ Alexander Fleming discovers penicillin
â—¦ Discovered by accident
â—¦ Used to treat Streptococci, Staphylococci, Meningococci, and
diphtheria
â—¦ Penicillin is a natural antibiotic (naturally produced)
â—¦ Dorothy Hodgkin determined chemical structure of penicillin
â—¦ Allowed for modification of penicillin to make semisynthetic
antimicrobials
3
Chemotherapy
Generic term for use of chemicals
or drugs to treat disease
Antimicrobials
(3 types)
Drugs that treat infectious disease
(caused by microbial pathogens)
(1) Antibiotics
Antimicrobials naturally produced
by a microbe to destroy another
microbe
(2) Semisynthetics
Chemically altered antibiotics
(3) Synthetics
Completely synthesized in a lab
4
The Fundamentals
â—¦ Terms to know
◦ Bacteriostatic: bacteria can’t grow when chemical present but can grow if it is removed
â—¦ Bactericidal: bacteria killed
â—¦ Narrow spectrum: only targets a specific group of microbes
â—¦ Broad spectrum: targets a variety of microbe types
â—¦ Can lead to a superinfection in some individuals
â—¦ Secondary infection in those already having an infection
â—¦ Pseudomembranous colitis caused by Clostridium difficile
5
Clinical considerations in choosing Antimicrobial Agents
Dosage: amount of medication needed in a time interval
Need to kill microbe but with minimum of side effects
For Children based on mass (should that also be considered for adults?)
Dosage dependent on ability to metabolize and eliminate drug –
slower if liver or kidney dysfunction
Dosage dependent on Half life of drug =
rate at which 50% of drug eliminated from plasma
6
Clinical considerations in choosing Antimicrobial Agents
Route of Administration
Topical / Local
External application of drug
Oral
Easiest; but drug absorption possibly lower in
GI tract; can abuse
Intramuscular
(IM)
Hypodermic needle into muscle è drug diffuses
into blood; lower drug concentration than IV
Intravenous (IV)
Needle or catheter delivers drug directly into
bloodstream
Initial drug concentration high, but liver & kidney
remove rapidly; need continuous supply
Blood-brain
barrier
Blood vessels in brain, spinal cord, eye almost
impermeable to many drugs
Clinical considerations in choosing Antimicrobial Agents
Safety & Side Effects
Toxicity to tissues/organs (kidney, liver)
Allergic reactions
Suppression & alteration of normal microbiota causes
Superinfection
Antiprotozoan drug
metronidazole; breakdown
products of hemoglobin
Tetracycline forms
complexes w/calcium
8
Synergistic
Drug Interactions
2 drug combo has efficacy better than either drug
alone
Synergistic drug combos can also slow down drug resistance
Trimethoprim & Sulfamethoxazole: alone only bacteriostatic;
together are bactericidal
Antagonistic
Synergistic
enhancement of
antimicrobial
activity beyond the
activity of each
individual drug
Drug combos that have harmful effects
Loss of drug activity; decreased levels; toxicity
As first proposed by Ehrlich’s “Magic Bullet”,
successful drugs must have Selective Toxicity
= Drug must kill or inhibit microbe while causing minimal or no
harm to the host
Takes advantage of differences between
humans and microbial structures or metabolism
Easiest for bacteria: are the least like us and have many cellular
targets for drug inhibition
Most antimicrobials are anti-bacterials
Fungi, protozoa and helminths are more difficult because they are
eukaryotes
Helminths are very difficult to treat because they are animals
Hardest to get Selective Toxicity for viruses because they are
simple and are obligate intracellular pathogens that use our
enzymes for their replication
10
So there are the fewest anti-viral drugs
Mechanisms of Antimicrobial Drugs
11
Antifungal Drugs: take advantage of differences
(fungal vs human) in biosynthesis of sterols needed for
membrane fluidity and proper cell function
Ergosterol is a sterol lipid unique to fungal cell membranes
Is target of antifungal drugs
13
Antifungal Drugs
Imidazoles
Synthetic fungicides that disrupt ergosterol biosynthesis
Used in agriculture, for ringworm, athlete’s foot, jock itch,
tinea corporis, yeast infections, dandruff
Bind ergosterol in cell
membrane and create
pores that disrupt
membrane
Polyenes Nystatin for yeast infections
Amphotericin B for systemic
infections like
histoplasmosis,
blastomycosis, meningitis
Polyoxins
Target Chitin synthesis –
only found in fungal cell
walls
For agriculture
Antiprotozoan Drugs
Artemisinin
Antimetabolite – metabolized by cells to produce
damaging reactive oxygen species (ROS)
Used in combo with other drugs for Malaria =
Artemisinin-based combination therapy (ACT)
Nitroimidazoles
Inhibits nucleic acid synthesis
Treats Giardia lamblia, Entamoea histolytica,
Trichomonas vaginalis
Quinolines
Inhibit heme
detoxification necessary
for Plasmodium’s
effective hemoglobin
breakdown (as amino
acid source) inside
RBCs
Treats Malaria
Malaria caused by
Plasmodium
Antihelminthic Drugs – selective toxicity difficult
Benzimidazoles
Prevents microtubule formation in worms, reducing
glucose uptake
Broad spectrum – helminths, protozoans, fungi,
viruses
Mebendazole, albendazole
Ivermectin
Binds chloride channels blocking neuronal
transmission causing starvation, paralysis and death
Treats roundworms (also mites, lice, bed bugs)
Praziquantel
Induce calcium influx
resulting in spasms and
paralysis
Treats tapeworms, liver
flukes,
Schistosoma blood flukes
Antiviral Drugs – selective toxicity extremely difficult
Several Mechanisms of Action that inhibit different stages of viral life cycle
Blocks DNA replication
Competitive Inhibitor of Reverse
Transcriptase
Binds and inhibits Reverse
Transcriptase
Blocks release of virus from infected cells
Inhibition of Protease: blocks viral protein
processing and prevent maturation
Inhibition of Integrase: blocks integration of
HIV genome into host chromosome
Inhibition of HIV and Host Cell Membrane
Fusion
Antiviral Therapy for HIV
18
Drug Resistance Mechanisms of Action
= How the microbe stops the drug from working effectively
Not shown:
Target overproduction
Target Mimicry
Enzymatic bypass
19
Drug Resistance Mechanisms of Action
1. Drug Modification or Inactivation
Penicillinase =
Beta
lactamase
2. Cellular Uptake Prevention or Efflux
Can also alter:
• Outer membrane lipid
composition
• Number of porin channels
and their selectivity
Production of efflux pumps
Uptake prevention and/or efflux
decreases drug concentration
so not enough drug inside cell to
be effective
20
Drug Resistance Mechanisms of Action
3. Target Modification
Microbial targets of drugs change so drug no longer
binds.
Examples:
• Penicillin-binding proteins (PBPs) no longer bind Beta-lactam drugs
4. Target Overproduction: Microbial enzyme that drug targets gets
overproduced so microbe has enough enzyme to carry out required reactions
5. Enzymatic Bypass
21
Drug Resistance Mechanisms of Action
6. Target Mimicry
Microbe produces proteins that bind drug
and prevent it from binding microbial target
Example:
Mycobacterium
tuberculosis
produces a protein
that looks like DNA
and binds
Fluoroquinolones
22
Drug Resistance
Multidrug-resistant Carry one or more drug resistance
microbes (MDRs) mechanisms of action making them
resistant to multiple antimicrobials
= “Superbugs”
Cross-resistance
A single drug resistance mechanism
of action that makes microbe
resistant to multiple antimicrobials
Superbugs responsible for > 2 million infections/year in
U.S. and 23,000 fatalities
ESKAPE Superbug pathogens that cause lots of
nosocomial infections:
Enterococcus faecium, Staphylococcus aureus,
Klebsiella pneumoniae, Acinetobacter baumannii,
Pseudomonas aeruginosa, and Enterobacter 23
Testing the Effectiveness of Antimicrobials
Kirby-Bauer Disk Diffusion Susceptibility Tests
Swab plate w/microbe; place disks w/drugs that diffuse
Zone of Inhibition
Clear area where bacteria killed
Larger zone diameter = more effective drug
Microbe is
Resistant to drug
on disk
Diameter of zone of
inhibition
– Microbe is
Sensitive to drug
on disk
24
Testing the Effectiveness of Antimicrobials
Minimum Inhibitory Concentration (MIC):
Lowest concentration of drug that inhibits visible bacterial growth
Minimum Bactericidal Concentration (MBC):
Lowest drug concentration that kills ≥ 99% of starting inoculum
Macrobroth
dilution test
Bacteria added to different concentrations of an
antimicrobial in broth è grow & measure turbidity
1.6 mcg/ml is
Minimum
Inhibitory
Concentration
(MIC) of drug
25
Tests that Measure Effectiveness of Antimicrobials
Etests can determine MIC
(1) Plate swabbed w/microbe
(2) Strip w/gradient of antimicrobial placed on plate
(3) Elliptical zone of inhibition formed
0.75 μg/ml is
Minimum
Inhibitory
Concentration
(MIC) of drug
26
Current Strategies for Antimicrobial Discovery
Extensive screening and testing of soil and microbial metabolic
products for antimicrobial activity
Combinatorial chemistry: makes large number of compounds from
simple precursors to test for antimicrobial activity
Developing drugs that inhibit resistance mechanisms of action or
that target virulence factors
Development of drugs very expensive and time consuming
(12 – 24 years); only 5 pharmaceutical companies developing
27
BIOS 350
CHAPTER 15
MICROBIAL MECHANISMS OF PATHOGENICITY
1
Signs and Symptoms of Disease
â—¦ Infection: the successful colonization of
a host by a microorganism
â—¦ Disease: any condition in which the
normal structure or functions of the
body are damaged or impaired
â—¦ Signs: objective and measurable, and
can be directly observed by a clinician
â—¦ Symptoms: are subjective they are felt
or experienced by the patient, but
they cannot be clinically confirmed or
objectively measured
â—¦ A specific group of signs and
symptoms characteristic of a particular
disease is called a syndrome
2
Classifications of Disease
â—¦ Asymptomatic or subclinical: meaning
they do not present any noticeable
signs or symptoms
â—¦ Infectious disease: any disease caused
by the direct effect of a pathogen
â—¦ Communicable: capable of being
spread from person to person through
either direct or indirect mechanisms
â—¦ Contagious diseases: easily spread
from person to person
â—¦ Nosocomial diseases: acquired in
hospital / healthcare settings
â—¦ Zoonotic disease: not transmitted
between humans directly but can be
transmitted from animals to humans
â—¦ Noncommunicable disease: not
spread from one person to another
â—¦ Noninfectious diseases: not caused by
pathogens
â—¦ Iatrogenic diseases: contracted as the
result of a medical procedure are
known as iatrogenic diseases
â—¦ occur after procedures involving wound
treatments, catheterization, or surgery if
the wound or surgical site becomes
contaminated.
3
Periods of Disease
4
Acute and Chronic Diseases
â—¦ Acute disease: pathologic changes occur
over a relatively short time (e.g., hours,
days, or a few weeks) and involve a rapid
onset of disease conditions
â—¦ Examples: Influenza, colds, etc.
â—¦ Chronic disease: pathologic changes can
occur over longer time spans (e.g., months,
years, or a lifetime)
â—¦ Helicobacter pylori
â—¦ Hepatitis B
â—¦ Latent diseases: pathogen goes dormant
for extended periods of time with no active
replication
â—¦ Herpes virus infection
5
Koch’s Postulates
â—¦ (1) The suspected pathogen must be
found in every case of disease and not
be found in healthy individuals.
â—¦ (2) The suspected pathogen can be
isolated and grown in pure culture.
â—¦ (3) A healthy test subject infected with
the suspected pathogen must develop
the same signs and symptoms of
disease as seen in postulate 1.
â—¦ (4) The pathogen must be re-isolated
from the new host and must be
identical to the pathogen from
postulate 2.
6
Pathogenicity and Virulence
â—¦ Pathogenicity: ability of a microbial
agent to cause disease
â—¦ Virulence: degree to which an
organism is pathogenic
â—¦ ID50: the number of pathogen cells
or virions required to cause active
infection in 50% of inoculated
animals
â—¦ LD50: the number of pathogenic
cells, virions, or amount of toxin
required to kill 50% of infected
animals
7
Primary Pathogens versus
Opportunistic Pathogens
â—¦ Primary pathogen: can cause disease
in a host regardless of the host’s
resident microbiota or immune system
â—¦ Opportunistic pathogen: can only
cause disease in situations that
compromise the host’s defenses, such
as the body’s protective barriers,
immune system, or normal microbiota
8
Stages of Pathogenesis
â—¦ Exposure
â—¦ An encounter with a potential pathogen
â—¦ Portal of entry
â—¦ An anatomic site through which
pathogens can pass into host tissue
â—¦ Parenteral route
â—¦ Pathogens enter through a breach in the
protective barriers of the skin and
mucous membranes
9
Adhesion and Invasion
â—¦ The pathogen adheres at the portal of
entry
â—¦ Adhesins are found on the surface of
certain pathogens and bind to specific
receptors (glycoproteins) on host cells
â—¦ Fimbriae
â—¦ Invasion involves the dissemination of a
pathogen throughout local tissues or
the body
â—¦ Exoenzymes or toxins
â—¦ Causes damage to tissues allowing
pathogen to spread
â—¦ Flagella
â—¦ Glycocalyx
10
Infection
â—¦ Local infection: confined to a small
area of the body, typically near the
portal of entry
â—¦ Staphylococcus aureus
â—¦ Focal infection: a localized pathogen,
or the toxins it produces, can spread to
a secondary location
â—¦ Primary infection the initial infection
caused by one pathogen
â—¦ Influenza
â—¦ Secondary infection: infection that
occurs after a primary infection due to
a compromised immune system
â—¦ Haemophilus influenzae
â—¦ Streptococcal species
â—¦ Systemic infection: an infection
becomes disseminated throughout the
body
â—¦ Chickenpox
11
Transmission of Disease
â—¦ Portal of exit
â—¦ Pathogen transmitted to a new
host
12
Important Terms
â—¦ The presence of bacteria in blood is called
bacteremia
â—¦ Viruses are found in the blood, it is called viremia
â—¦ Toxemia describes the condition when toxins are
found in the blood
â—¦ Bacteria are both present and multiplying in the
blood, this condition is called septicemia
â—¦ Patients with septicemia are described as septic
â—¦ Can lead to shock , a life-threatening decrease in
blood pressure (systolic pressure 1 meter to respiratory mucous membranes of new host via aerosol:
is Airborne (type of Vehicle transmission)
7
Contact Transmission: movement of pathogen between
hosts due to contact between them
Direct
Contact
2 types
Vertical Transmission: Mother to child
Horizontal Transmission: Person-to-person
touching, kissing, sex, bodily fluid
exchange
Droplet Transmission: Droplets of mucus
from coughing, sneezing with < 1 meter travel distance Indirect Contact Fomites – inanimate objects Needles, toys, money, drinking glasses, medical equipment, door handles Vehicle Transmission Transfer of pathogen between hosts via contaminated air, drinking water, food Airborne Mucous droplets or desiccated droplet nuclei that travel > 1 meter to respiratory mucous
membranes of new host
Aerosols – cloud of dust and fine particles
suspended in air that carry pathogens
Waterborne
Fecal-oral infection of GI diseases
Foodborne
Inadequately processed, undercooked,
poorly refrigerated
Vector Transmission: Arthropods that transmit diseases from one host
to another
2 TYPES:
Mechanical Transmission via Mechanical Vector: arthropod is not
infected with pathogen but carries it on its body
Biological Transmission via Biological Vector: pathogen is inside
arthropod; is in gut (feces) or salivary gland
Modes of
Infectious
Disease
Transmission:
Summary and
examples
Healthcare-Associated (Nosocomial) Infections (HAIs)
Infections acquired in health-care facilities, including
hospitals
Patient do not have infection when admitted to health-care
facility, but do have compromised immune systems
Types: surgical sites, pneumonia, urinary tract infections,
blood infections from contaminated surgical or medical
instruments
CDC: 2015 HAIs in U.S.
Incidence: 687,000 new cases
(has gone down recently)
Mortality: 72,000
CDC HAI information
World Health Organization (WHO)
United Nations agency for international public health
issues
$4 billion budget in 2015
Monitors, reports, develops, and implements strategies
for disease control and prevention
Vaccinations, educational outreach, emergency
responses
WHO and CDC monitor and prepare for Emerging and
Reemerging Infectious Diseases
Emerging
new disease or an increase in prevalence in
past twenty years (Ebola)
Reemerging
a disease increasing in frequency after
previous period of decline (TB, malaria,
bacterial pneumonia, gonorrhea, syphilis)

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