Microbiology Exam 1

When was the Golden age of Microbiology?

1850-1915

Louis Pasteur

“Father of Microbiology”

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Discovered/worked with fermentation + pasteurization

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Domesticated yeast - bakers and brewers

*Saccharomyces cerevisiae*

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Created Germ Theory of Disease in 1857

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BJ Palmer Germ Theory Quote

“If the Germ Theory of Disease were correct, there’d be no one living to believe it.” - BJ Pamer, As A Man Thinketh, 1921

Dr Drover Revised Germ Theory Quote

“If the Germ Theory of Disease were there *only* truth, there’s be no one living to believe it.” - Dr Drover

Preventing Infection and Disease

Semmelweis → Handwashing

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Lister → Antiseptic technique

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Snow → Infection control, field of epidemiology

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Jenner → Smallpox vaccine, field of immunology

Ignaz Semmelweis

Found that medical students had a 20x higher mortality rate than midwives in deliveries of babies.

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Hypothesized “cadaver particles” from hands of medical students caused “puerperal fever”

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Required washing hands, saw the mortality rate go down to less than 1%.

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His views were considered radical, opposed, and he was driven out of the hospital.

Joseph Lister

Surgeon, noted problems with infection in wounds.

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Began spraying wounds, incisions, and dressings with carbolic acid → decreased deaths by 2/3 among his patients

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Known as antisepsis, the method was accepted into common practice.

John Snow

Discovered cause of cholers transmission

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Created first outbreak map, found it centered on a water supply.

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Stopping access to source stopped cases.

Edward Jenner

Showed that vaccination with pus collected from cowpox lesions prevented smallpox.

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Created field of immunology

Processes of Life

Growth

Reproduction

Responsiveness

Metabolism

Prokaryotic vs Eukaryotic Cells

Prokaryotes →

No nucleus

Circular DNA

Smaller

Simple structure

Bacteria and archaea

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Eukaryotes →

Nucleus

Linear DNA

Larger

Complex structure

Protozoa, fungi, animals, plants, algae

Bacterial Cell Walls

Give bacterial cells structure, characteristic shape, and protection from osmotic forces

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Assists some cells in attaching to other cells or resisting antimicrobial drugs

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Composed of peptidoglycan

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Most common types of bacterial cells walls: Gram + & Gram -

Categories of Bacteria

*See Image*

Gram (+) Bacteria

Cell wall

Thick layer of peptidoglycan

Appear *PURPLE* following Gram Stain

Gram (-) Bacteria

Cell Wall

Thin layer of peptidoglycan

Membrane contains Lipopolysaccharide known as Lipid A

\- Lipid A = endotoxin

*May trigger fever, vasodilation, inflammation, shock, and blood clotting. May be impediment to tx of disease.*

Appears *MAGENTA/RED* following Gram Stain

Categories of Bacteria

Acid Fast Bacteria →

Cell Wall

Contains waxy, mycolic acid

Mycobacterium

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No Cell Wall Bacteria →

Distinctive “fried egg” appearance when grown on media

Colonize osmotically protected habitats such as animals or the human body.

Mycoplasma

A typical bacterial cell (with a cell wall) which has a solute concentration of .85% NaCl is placed into a solution that has a .2% NaCl concentration, what will happen?

It will take on water but has no risk of bursting.

Effects of Solutions on Cells

*See Image*

Other Important Features of Bacteria

Inclusions →

May include reserve deposits of chemicals

Stored when nutrients are in abundance, used when nutrients are scarce

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Endospores →

Unique structures produced by some bacteria that are a defensive strategy against unfavorable conditions

Only produced by organisms in Genus Bacillus and Clostridium

Non Membranous Organelles: Ribosomes

Sites of *protein synthesis* of a cell

Subunits size expressed in Svedbers (S)

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Prokaryotic ribosomes are 70S (composed of 30S and 50S subunits)

*Yes, that’s not accurate math, it’s still the answer*

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Eukaryotic ribosomes are 80S (composed of 40S and 60S subunits)

*BUT* mitochondria and chloroplasts have 70S ribosomes.

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Why does this matter? -- Important target for antimicrobial drugs!

General Principles of Microscopy

Resolution →

The shortest distance between two points on a specimen that can still be distinguished by the observer as separate entities

Ability of a lens to separate or distinguish small objects that are close together

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Contrast →

Differences in intensity between two objects or between an object and background

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Staining →

Increases contrast and resolution by coloring specimens with stains/dyes

Staining

*See Image*

Gram Stain (Bacteria)

1. Crystal violet primary stain
2. Decolorize


1. Washes gram (-) cells of stain due to their thinner walls.
3. Counter stain (safranin)


1. Gram (-) cells take on magenta/red color

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Results:

Purple - Gram (+) cells

Magenta (red) - Gram (-) cells

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Mycobacteria

Group of bacteria that do not have the typical peptidoglycan cell walls

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Their cell walls have a high, waxy, mycolic acid content, making them resistant to decolorization by acids during staining procedures such as the Gram stain.

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Referred to as “Acid-Fact Bacteria”

Acid-Fast Stain (Bacteria)

1. Carbol fuchsin primary stain
2. Decolorize (alcohol flush)


1. Acid-fast cells retain their red color because acid cannot penetrate the waxy wall
3. Counterstain (methylene blue)


1. Stains only bleached, non-acid-fast cells

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Results:

Red Acid Fast cells

Blue Non-Acid Fast cells (including human cells and tissues)

Endospore Stain (Bacteria Bacillus and Clostridium)

1. Malachite Green Primary Stain


1. Use heat to drive into the endospore
2. Decolorize


1. Just uses water here
3. Counterstain (safranin)

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Results:

Green endospores

Magenta (Red) vegetative cells

Classifying Prokaryotes

*Medically important groupings and genera of bacteria!*

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Know the rules, memorize exceptions!

Genus name ends in -us or -um = Gram (+)

Genus name ends in -a or -er = Gram (-)

Gram (+) Bacteria

*End in -us or -um*

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Bacillus (anthrax)

Clostridium (tetanus, gas gangrene, botulism)

**Exeption** - Listeria (food poisoning)

Propionibacterium (acne)

Staphylococcus (abscesses, skin infections)

Streptococcus (strep throat, dental caries)

Lactobacillus, Bifidobacterium (good bacteria)

Gram (-) Bacteria

*End in -a or -er*

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Bartonella (cat scratch dx)

Bordetella (pertussis)

Borellia (lyme dx)

Brucella (brucellosis)

Campylobacter (food poisoning)

Chlamydia (chlamydia, trachoma)

Citrobacter (nosocomial catheter UTIs)

Escherichia (traveler’s diarrhea, UTIs)

Francisella (tularemia)

**Exception** - Haemophilus (meningitis, pinkeye, chancroid)

Klebsiella (pneumonia)

Legionella (lengionnaire’s dx)

Leptospira (kidney infection)

Neisseria (gonorrhea, meningitis)

**Exception** - Proteus (UTIs)

**Exception** - Pseudomonas (folliculitis, burns, infection)

Rickettsia (RM spotted fever)

Salmonella (food poisoning, Typhoid fever)

Serratia (nosocomial catheter UTIs)

Shigella (dysentery)

Treponema (syphilis)

**Exception** - Vibrio (cholera)

Yersinia (bubonic plague, food poisoning)

Taxonomy: Linnaeus

System classified organisms based on characteristics in common

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Used binomial nomenclature

*Genus Species*

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Proposed only 2 kingdoms: Animals and Plants

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Taxonomy: Carl Woese

Compared nucleotide sequences of rRNA subunits

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Proposed three domains as determined by ribosomal nucleotide sequences

*Eukarya, Bacteria, Archaea*

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Cells within three domains differ with respect to many other characteristics

Microbial Growth

When speaking of reproductive activities of microbes, use the term growth to refer to an increase in the size of a population of microbes

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Colony - An aggregation of cells arising from a single parent cell

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Biofilm - A collection of microbes in a complex community

Growth Styles

*See Chart*

7 Growth Requirements

Oxygen

\- Microorganisms vary widely in their oxygen requirements for growth

*Aerobe or Anaerobe*

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Temperature

\- As a rule, temperature is the most important factor affecting the growth of microorganisms

*Organisms can grow within a range of temperatures*

Psychrophilic: Prefer cold temps

Mesophilic: Prefer moderate temps, near normal body temp, most pathogenic organisms

Hyper Thermophilic: Prefer higher temps

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pH

\- Most microorganisms thrive in a pH range of 6-9

Most animal pathogens work best near a pH of 7

“Pickling” or preserving food may be accomplished in an acidic medium - vinegar

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Moisture

\- Vegetative cell maintenance and growth requires water

Food and waste are transported through the cell wall in water solutions.

Water is a building material necessary in cell synthesis

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Osmotic Pressure

\- Pressure created by osmosis

Cell in hypertonic environment: water is drawn out of cell

*Cell shrinks and may die - Crenation*

Cell in hypotonic environment: water is drawn into the cell

*Cell shrinks or may even burst - Lysis*

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Light

\- Microbes also vary widely in their light requirements

In comparison, most pathogens are killed by direct sunlight

Both UV rays and warmth harm bacteria

Green and purple pigmented bacteria use light as an energy source

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Food

\- Organisms require food for building cell components and proteins and for the energy necessary for cell survival

Microbial activity is limited when food supplies become exhausted

The amount and type of food available will have an impact on the organism’s survival and growth - Inclusions

Culturing Microorganisms

Culture Media

\- Some microbes are not particular and cab be grown in a variety of media, others require specific nutrients

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→ Selective Media

Contains substances that favor or inhibit the growth of particular organisms

Dyes or salts added, specific nutrients left out

Ex. Sabouraud detrose agar - Inhibits bacteria, selects for fungi

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→ Differential Media

Presence of visible changes in medium or differences in the appearance of colonies help differentiate organisms

Ex. Blood agar - Streptococcus change appearance of blood

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→ Both Selective and Differential Media

Will do both, will be selective but will also help differentiate between organisms

Ex. MacConkey agar - Selective for gram (-) bacteria and types within the negatives.

The structure of Prokaryotic Genomes

Plasmids (aka Factors)

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Small molecules of extra-chromosomal DNA that replicate independently

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Not essential for normal metabolism, growth, or reproduction

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Can confer survival advantages

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Types:

\- Fertility factors (F plasmids)

*Carry instructions for conjugation*

\- Resistance factors (R Plasmids)

*Carry genes for resistance to abx*

\- Bacteriocin factors

*Carry genes for toxins called bacteriocins - can kill its competitors*

\- Virulence factors

*Carry instructions that enable bacterium to become pathogenic*

Genetic Transfer

Vertical Gene Transfer

\- Organisms replicate their genomes and provide copies to descendants

\- Normal process in both prokaryotes and eukaryotes

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Horizontal Gene Transfer

\- Aquire genes from other microbes of the same generations

\- Donor cell contributes part of genome to recipient cell

*May be different species*

3 Types:


1. Transformation


1. Recipient cell takes up DNA from environment can include DNA from dead organisms
2. Cells that take up DNA are called competent
3. Occurs in only a few types of bacteria
2. Transduction


1. Transfer of DNA from one cell to another via a replicating virus
2. Generalized - transducing phage carries random DNA segment from donor to recipient
3. Specialized - only certain donor DNA sequences are transferred
3. Bacterial conjugation


1. Transfer of DNA from one cell to another, mediated by conjugation pilli
2. Donor cell requires F plasmid (F+)
3. Recipient cell lacks F plasmid (F-)

Typical Prokaryote Morphologies

*See Image*

Reproduction of Prokaryotic Cells

All reproduce asexually

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3 Main Methods:


1. Binary Fission (most common)
2. Snapping Division


1. Clostridium and Corynebacterium
3. Budding

Eukaryotic Microbes of Clinical Interest

Fungi and Protozoa - Microscopic

Protozoa and Helminths - “parasites”

Reproduction of Fungi

Budding, spore formation

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*most also reproduce sexually*

Protozoa

Typically lack a cell wall

Require moist environments (waterborne illnesses)

Very few are pathogens!

Characterized by great morphological diversity

Most reproduce asexually only

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All have trophozoite

*Motile feeding stage*

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Some have cysts form, many pathogens are in cyst like forms that we ingest

*Hardy resting stage*

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Some have contractile vacuoles

*Actively pump water from the cells, protecting them from osmotic lysis*

Effects of Solution on Cells

*See Image*

Characteristics of Viruses

Miniscule, acellular (no presence of life)

Infectious agent having either DNA or RNA

Cause infections of humans, animals, plants, and bacteria

Cause most of the diseases that plague the industrialized world

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Extracellular State →

\- Called a viron

Protein coat (capsid) surrounding a nucleic acid core

Together the capsid and nucleic acid are called the nucleocapsid

Some have a phospholipid envelope

*Provide protection for viral nucleic acid and means of attachment to host cell*

Envelope virus versus non envelope virus

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Intracellular State →

\- Once the virus is inside the host, the capsid is removed

*Virus exists simply as nucleic acid*

Hosts of Viruses

Specific →

HIV specifically attacks helper T lymphocytes in humans

*Has no effect on human muscles or bone cells*

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Generalist →

West Nile Virus

*Can infect most species of birds, several mammalian species (including humans), and some reptiles*

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**ALL types of organisms are susceptible to some sort of viral attack**

Viral Capsid Shapes

Polyhedral

\- Geodesic dome

\- Most common viral shape → icosahedron(20 sides)

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Complex

\- Capsids of many shapes

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Helical

\- Spiral

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Viral Replication

Lytic Replication →

\- Synthesis of new nucleic acids and viral proteins by host cell

\- Assembly of new virions within host cell

\- Release of new virions from host cell, typically lyse the host cell

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Lysogeny → Modified Replication Cycle

Infected host cells grow and reproduce normally for generations before they lyse.

*Prophages - inactive phages*

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Lysogenic Conversion → When phages carry genes that alter phenotype of a bacterium

Can turn bacterium from harmless to pathogen

Can happen with animal/human cells too

Latency of Animal Viruses

When animal viruses remain dormant in the host cells

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Called Latent Viruses

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May go years with no viral activity

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Some latent viruses never become incorporated into host chromosome

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If it happens, incorporation of latent virus into host DNA is permanent

Prions

Prions → Proteinaceous infectious agents, lack nucleic acid

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Prion PrP converts cellular PrP into prion PrP

\- By inducing conformational change

\- Cellular PrP made by all mammals and has a-helices

\- Prion PrP is disease causing form with b-sheets

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Prions only destroyed by:


1. Incineration
2. Autoclaving in sodium hydroxide

Prion Diseases

Most prominent in Nervous System tissues

Large vacuoles form in brain

\- Characteristic spongy appearance

Spongiform Encephalopathy

\- Bovine Spongiform Encephalopathy (BSE)

\- Variant Creutzfeldt Jacob Disease (vCJD)

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*Prions composed of different proteins may lie behind other muscular and neuronal degenerative diseases*

Alzheimers, Parkinsons, ALS

Foodborne Illnesses

Symptoms:

\- Nausea, vomiting, diarrhea, fever, fatigue, muscle cramps

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2 Types:


1. Food Infections


1. Consuming living microorganisms
2. Food Intoxications


1. Consume microbial toxins, NOT the microbe

Top Germs Causing Illness

*See chart*

Waterborne Illnesses

Consuming contaminated water can cause various diseases

*Diarrheal dx occur worldwide*

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Water treatment removes most waterborne pathogens

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*See chart for diseases caused*

Water Treatment

Potable Water → water considered safe to drink

\- Water is not devoid of microorganisms and chemicals

\- Levels are low enough that it is not a health concern

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Coliform Bacteria → Indicator of sanitary quality

\- Coliforms not normally causes of serious illness, but they are easy to culture and the presence of coliforms indicates fecal contamination.

*Increased likelihood that disease-causing microbes are present*

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Treatment of Water →

\- Municipal water treatment

aka drinking water - clean water that is used in homes and businesses

\- Wastewater treatment

aka sewage - water that leaves homes or businesses after use

Bioremediation

Remediate - To solve a problem

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Bio-remediate - to use biological organisms to solve an environmental problem such as contaminated soil or groundwater

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Use organisms to clean up toxic, hazardous, or recalcitrant compounds by degrading them to harmless compounds.

Biological Warefare and Bioterrorism

Bioterrorism →

Uses microbes or their toxins to terrorize human populations

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Agroterrorism →

Uses microbes to terrorize human populations by destroying the food supply

Criteria for Assessing Biological Threats to Humans

Public Health Impact

\- Ability of hospitals and clinics to handle the casualties

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Delivery Potential

\- How easily agent can be introduced into the population

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Public Perception

\- Effect of public fear on ability to control an outbreak

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Public Health Preparedness

\- Existing response measures

Biosafety Levels

(by CDC)

Biosafety Level 1

\- Handling pathogens that do not cause disease in healthy humans

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Biosafety Level 2

\- Handling of moderately hazardous agents

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Biosafety Level 3

\- Handling of microbes in safety cabinets

\- May cause serious or potentially lethal disease after inhalation

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Biosafety Level 4

\- Handling of microbes that cause severe or fatal disease

Normal Microbiota

aka normal flora or indigenous microbiota

Organisms that colonize the body’s surfaces without normally causing disease

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Resident Microbiota →

Remain part of normal microbiota of a person for life

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Transient Microbiota →

Remain in body for few hours, days, months before disappearing

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Acquisition of Normal Microbiota

Axenic: Sites that are free of any microbes and are not supposed to be colonized by normal flora:

\- Alveoil of lungs

\- Central Nervous System

\- Circulatory System

\- Upper Urogenital Regions

\- Uterus

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In Utero → No exposure to microbiota (uterus is axenic)

Begin to develop during birthing process

\- Mouth and nose through birth canal

\- First breath

\- handling by staff, family, people

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Much of one’s resident microbiota established during first months of life.

Opportunistic Pathogens

Normal microbiota that cause disease under certain circumstances

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Conditions that provide opportunities:

\- Induction into unusual site in body

*E. coli mutualistic in colon, but if it enters the urethra becomes opportunistic*

\- Immune suppression

*AIDS and cancer from patients often die from opportunistic infections*

\- Changes in the normal microbiota

*Take antibiotics, kills normal flora also, allows opportunistic yeast infection*

\- Stressful conditions

*Anything that strains a person’s normal metabolism or emotional state*

Reservoirs of Infectious Diseases

The habitat in which an organism normally lives, grows, and multiplies

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3 Types:


1. Animal Reservoirs


1. Zoonoses - diseases naturally spread from animal host to humans


1. Acquired through direct contact with animal or it’s waste, eating animals, bloodsucking arthropods
2. Humans are usually a dead end host - humans get dieases from animals, animals do not get diseases from humans
2. Human Carriers
3. Nonliving Reservoirs

Strategies to Limit the Spread of Disease

Isolation →

Used to separate and restrict the movement of ill persons who have an infectious disease

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Quarantine →

Used to separate and restrict the movement of well persons who may have been exposed to an infectious disease

Non living Reservoirs

Soil, water, and food can be reservoirs of infection

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Sometimes the environment is conducive to growth of microbe

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Sometimes the presence of microorganisms is due to contamination by feces or urine

Exposure to Microbes

Contamination →

The mere presence of microbes in or on the body

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Infection →

When a pathogenic organism successfully evades body’s external defenses and becomes established in the body.

*May or may not result in disease*

Portals of Entry

Sites through which pathogens enter the body

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3 Major Paths:


1. Skin


1. Openings or cuts
2. Hair follicules or sweat glands
3. Burrowing into or digesting outer layers of skin
2. Mucous Membranes


1. Line the body cavities that are open to the environment
2. Provide a moist, warm environment hospitable to pathogens
3. Respiratory tract is the most common site of entry (nose, mouth, eyes)
4. GIT *MAY* be route of entry… must survive pH of stomach.
3. Placenta


1. Typically forms effective barrier to pathogens


1. Pathogens may cross the placenta and infect the fetus
2. Can cause spontaneous abortion, birth defects, premature birth.

*Parenteral Route is technically NOT a portal of entry, but a way to circumvent the usual portals of entry*

\- Not a true portal of entry, pathogens deposited directly into tissues beneath the skin or mucous membranes.

Symptoms

Subjective characteristics of disease felt only by the patient

Signs

Objective manifestations of disease observed or measured by others

Syndrome

Group of symptoms and signs that characterize a disease or abnormal condition.

Terminology of Disease

*See Image*

Triad or Triangle of Health

When these 3 are in normal balance health results.

When out of balance, disease results.

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Host → Environment → Agent

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*Infectious disease transmission occurs when a susceptible host and a pathogenic agent exist in an environment conducive to disease transmission.*

The Nature of Infectious Disease

Disease →

Results if the invading pathogen alters normal body functions (aka morbidity)

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Virulence →

Degree of pathogenicity (how easy is it for the organism to cause disease)

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Severity →

The extent of organ system derangement or physiologic decompensation for a patient (how harmful is the disease)

Virulence Factors

Contribute to Virulence

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Adhesion factors/Biofils

Extracellular enzymes

Toxins

Antiphagocytic factors

Stages of Infectious Disease

Incubation Period

Prodromal Period

Illness

Decline

Convalescence

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*See image for details*

Portals of Exit

How pathogens leave the host - Many are the same as portals of entry

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Bodily secretions

*Earwax, tears, nasal secretions, saliva, sputum, respiratory droplets*

Blood

Vaginal secretions or semen

Breastmilk

Bodily wastes

*Urine, excrement, sweat*

Modes of Transmission

Contact →

DIrect, indirect (fomites), droplets

*Fomites = inanimate object involved in indirect transmission*

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Vehicle →

Airborne, waterborne, foodborne, fecal-oral, bodily fluids

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Vector →

Arachid, insect

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Preinatal →

Mom to baby

Disease Vectors

Vectors are Arthropods that transmit pathogens

\- Insects, arachnids

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Mechanical vectors: passively carry the pathogens only

\- Flies, cockroaches

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Biological vectors: serve as host for pathogen

\- Mosquitoes (most common of all vectors)

\- Ticks, fleas, lice, tse tse flies, sand flies, reduviid bug, mites

Epidemiology

Frequency or occurrence of disease

Incidence →

Number of new cases of a disease in a given area/population during a given period of time

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Prevalence →

Number of total cases of a disease in a given area/population during a given period of time

Case Fatality Rate

Number of fatalities divided by the number of confirmed cases

Crude (population) Mortality (fatality) Rate

Number of fatalities divided by the total population

Epidemiology

Frequency/Geography of Disease

Endemic →

Disease that typically occurs at regular intervals at a relatively stable incidence within a given population or geographical area

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Sporadic →

Only a few scattered cases within an area or population

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Epidemic →

Occurs at a greater frequency than is usual for an area or population

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Pandemic →

An epidemic that occurs simultaneously on more than one continent

Healthcare-Associated Infections (HAIs)

aka Nosocomial infections

Exogenous →

Pathogen acquired from the HC environment

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Endogenous →

Normal microbiota within the patient become pathogenic due to factors in the HC setting

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Iatrogenic →

Results from modern medical procedures

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*Control = Hand washing! → Most effective way to reduce nosocomial infections*

Notifiable Diseases

*See image*

Basic Principles of Microbial Control

Sterilization →

Removal or destruction of all microbes, including viruses and bacterial endospores, in or on an object

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Aseptic →

An environment or procedure that is free of contamination by pathogens

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Disinfection →

Use of physical or chemical agents known as disinfectants to inhibit or destroy microorganisms

*Does not guarantee that all pathogens are eliminated*

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Antisepsis →

When a chemical used on skin or other tissue (human tissue), the process is called antisepsis and the chemical is called an antiseptic

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Degerming →

Removal of microbes from a surface by scrubbing

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Sanitization →

Process of disinfecting places and utensils used by the public to reduce the number of pathogenic microbes to meet accepted health standards

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Pasteurization →

Use of heat to kill pathogens and reduce the number of spoilage microorganisms in food and beverages

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\-stasis/-static →

Suffixes to indicate that a chemical or physical agent inhibits microbial metabolism and growth

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\-cide/-cidal →

Refers to agents that destroy or permanently inactivate a particular type of microbe

Relative susceptibility of microorganisms

Prions, endospores = most resistant

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Gram (+) bacteria, enveloped viruses = least resistant

Why are Gram (-) bacteria more resistant to antimicrobials?

They have a double phospholipid bilayer and lipid A in cell wall

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They tend to have more R plasmids

Physical Methods of Microbial Control

*See Image*

10 Major Categories: Chemical methods of microbial control

*See Image*

After performing the gram stain, you notice that the cells under the microscope are purple. What is the type of bacteria?

Gram +

Which of the following is used in protein synthesis?

Ribosomes

Which one of the following is a differential stain?

Gram stain

A cell would swell in what type of solution?

Hypotonic

Which one of the following would be most sensitive to antibiotics that interfere with peptidoglycan formation?

Gram +

Which one of the following would be most sensitive to change in tonicity?

Mycoplasma → Wall-less

Endospores are produced primarily by which of the following genera

Clostridium and bacillus

When performing an endospore stain the endospores will appear

Green

Plasmids that carry antibiotic resistance genes are called

R Factors

A rod bacterial cell shape is called what?

Bacillus

Bacteria that have a cell arrangement in a chain is called?

Strepto-

A square of four bacterial cells could be called what?

Tetrad

What is the most common type of bacterial cell division?

Binary fission