Basic Concepts Of Medical Microbiology

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Microbiology

Study of microscopic organisms

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Medical Microbiology

Study of the characteristics of pathogens

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Epidemiology

Study of health and diseases in populations

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Three Major Branches: Domains

Bacteria--> Prokaryotes

Archaea

Eukaryota--> Eukaryotes

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Prokaryotes

DNA: Yes--> Single Circle

Mitotic Division: No

Chromosomes: One

Membrane Bound Organelles: No

Ribosome Size: 70s (smaller)

Cell Wall w/ Peptidoglycan: Yes

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Eukaryotes

DNA: Membrane-Bound Nucleus (slower)

Mitotic Division: Yes

Chromosomes: Multiple

Membrane Bound Organelles: Yes

Ribosome Size: 80s (bigger)

Cell Wall w/ Peptidoglycan: No--> No Peptidoglycan

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Taxonomy

Domain

Kingdom

Phylum

Class

Order

Family

Genus

Species

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Viruses

Not alive

Must infect cell to reproduce

Obligate Intracellular Parasites

Contain DNA OR RNA --> NEVER BOTH

Target bacteria the most

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Obligate Intracellular Parasites

Must live inside other organisms

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Prions

Infectious proteins

Ingestion of infected meat

Cause Spongiform Encephalopathy

No Treatment/Fatal

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Protists

Microscopic Eukaryotes

-Algae + Slime Molds

-Protozoa + Fungi --> Cause Human Disease

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Most Impressive Pathogen?

Those that cause infection in healthy people

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Protozoa

Flagellates

Amebae

Sporozoa

Ciliates --> Paramecia

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Trypanosoma

SOI: Blood, Lymph

Transmission: Tse Tse Fly

Causes: Sleeping Sickness

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Plasmodium

SOI: Blood, Liver

Transmission: Mosquito Bite

Causes: Malaria

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Entamoeba

SOI: Colon, Liver, Organs

Transmission: Fecal/Oral

Caused By: Infected Water

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Giardia

SOI: Small Intestine

Transmission: Fecal/Oral

Caused By: Infected Water

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Crypotsporidium

SOI: Small Intestine, Respiratory Tract

Transmission: Fecal/Oral

Caused By: Infected Water

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Trichomonas

SOI: Vagina

Transmission: Sexual

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Acanthamoaeba

SOI: Brain, CNS, Eye

Transmission: Nasal Membrane/ Wound

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Fungi

Eukaryotic Heterotrophs

Yeasts, Dimorphic, Molds

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Yeasts

Unicellular

Reproduce by Budding

Cryptococcus/Candida

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Dimorphic

Endemic Fungi b/c Endemic to Certain Regions

At Room Temp--> Molds

Inhale Them--> Spread Through Body As Yeasts

Histoplasma

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Molds

Multicelluar

Reproduce By Spores--> We Inhale Them

Very Hard To Treat/ Infect Sick People

Lung Transplant and Cancer Patients

Aspergillus

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Size Comparison

Cells > Bacteria > Viruses > Molecules

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Bacteria

Prokaryotes --> No Nucleus

Simpler

No Visible Structures

Single Chromosome Of DNA

Rigid Cell Wall (Survive Hypotonic Environment)

Cocci --> Round

Bacilli --> Rods

Spirochetes --> Spiral

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Bacterial Capsule

Selectively Express or Lose

One of the ways vaccines are developed

Outermost layer

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Bacterial Cell Wall

Made of Peptidoglycan

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Bacterial Plasma Memebrane

Under Cell Wall

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Bacterial Cytoplasm

Contains:

Chromosomes

Nucleotoids

Extra Chromosomal DNA

Free Flowing Ribosomes (In EUKARY Rib fixed on RER)

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Bacterial Pilli (Fimbriae)

Help Adhere

May prevent being engulfed

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Bacterial Flagellum

Whip to move

Chemotaxis

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Chemotaxis

Attracted to chemicals for pathway

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Gram Stain Process

1. Fixation

2. Crystal Violent

3. Iodine Treatment

4. Decolorization w Alcohol

5. Counter Stain --> Safarin

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Gram (-) Cell Wall

Outer membrane

Leads to Intrinsic Resistance to Antibiotics

Porin Channels

Thin Layer of Peptidoglycan

Periplasmic Space

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Periplasmic Space

B/w Peptidoglycan and Cytoplasmic Membrane

Separates Cytoplasm from Cell Wall

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Gram (+) Cell Wall

Peptidoglycan

-Outermost layer, very thick

-Antibiotic has to diffuse through it

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Gram (+) Table

Outer Membrane: No

Peptidoglycan: Thick, Outermost

Teichoic Acids: Yes

Endotoxin: No

Porin Channel: No

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Gram (-) Table

Outer Membrane: Yes

Peptidoglycan: Thin, Covered by Outer Mem

Teichoic Acids: No

Endotoxin: Yes --> What Body Responds To

Porin Channel: Yes --> Antibiotic has to diffuse through peptidoglycan

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Porin Channels

Proteins through outer mem that allow nutrients ( and antibiotics) to diffuse

Antibiotics have to be relatively polar and hydrophilic to get through

Selectively Expressed --> Can evolve to stop expressing porin channels therefore antibiotics can't get in

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Endotoxin: Lipopolysaccharide (LPS)

Structural Component of Outer Mem

Responsible for Clinical Sepsis--> Promotes Pro Inflammatory cytokines in immune cells

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Bacterial Peptidoglycan

Series of Cross Linked Sugars In Cell Wall:

3 Steps:

  1. Production of monomers in cytoplasm
  2. Brought over to cell wall where they're lined up against each other to make chains
  3. Push chains together through "Cross Linking"

*Cant stretch out, must take apart and add

Bacteria break it down w autolysins and replace it to grow

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Bacterial Cytoplasmic Membrance

Separates cytoplasm from cell wall

Phospholipid bilayer

Secretes Cellular Material, transports molecules in

Daptomycin targets this

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Bacterial Capsule

Gelatinous Polysaccharide Layer covering bacterium --> Sugar Layer

Limits Phagocytosis

Antigentic--> Target for vaccine

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Bacterial Glycocalyx (Slime Layer)

Promotes Adherence

Biofilms--> slow growing, talkative bacteria

Promotes Drug Resistance

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Protein Synthesis

Proteins--> how organisms express their genetic info

In Bacteria, Fast (happening at same time)

In Humans, Slow (Happen step by step)

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DNA

Where its stored

Stores Genetic Info

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RNA

Where it goes to tell cell how to make proteins

Express Genetic Info

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Protein Syn--> Ribosomes

In cytoplasm, translate mRNA generated from transcription of DNA in genome

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Two Types of DNA of Bacteria

Chromosomal & Extrachromosomal

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Chromosomal

Like eukaryotes

Fixed --> There all the time

Nucleoid

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Nucleoid

"Naked" In cytoplasm

DNA Supercoils

Encodes for intrinsic antibiotic resistance

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Extrachromosomal

Found outside of the cell

Plasmids

Transposons

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Plasmids

** #1 GENETIC CAUSE OF ACQUIRED ANTIBIOTIC RESISTANCE **

Contains DNA outside of chromosome

Transmitted By Conjugation ---> transmit antibiotic resistance gene

Encode for virulence factors and antibiotic resistance

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Transposons

mobile genetic elements "jump" in other DNA

transmit antibiotic resistance

less common than plasmids

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Prokaryote Nucleiod

Looks like nucleus

no membrane bounding it in

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Eukaryote Nucleus

Membrane Bound Nucleus w/ Nucleolus

-Transcription occurs in nucleus to create mRNA that goes through pores to get to RER where the ribosomes are translated to proteins

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Nucleolus

Most DNA rich area

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Endospores

Dormant and highly resistance structures

no metabolic activity

Form when nutrients are poor

--> germinate into bacteria when nutrients available

difficult to eradicate

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When Bacteria Not Growing...

not affected by most antibiotics

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Virulence Factors

Factors that increase pathogenicity

Endotoxins, Exotoxins, Peptidoglycan, Pilli, Capsules, Destructive Enzymes

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Pathogenicity

Capacity to cause disease

Primary Pathogens

Opportunists

Amphibionts/ Commensals

Non-Pathogens

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Primary Pathogens

Cause disease in heathy people

Ex. Skin Infection

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Opportunists

Require compromised host or barrier to be pathogenic

not aggressive enough on their own

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Amphibonts/ Commensals

Mutualists that sometimes become pathogenic

ex. E. Coli

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Non-Pathogens

Most microorganisms

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As Pathogenicity increases

Frequency of it in nature decreases

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mRNA--> Messenger RNA

transcribed to/ list of directions on how to make protein

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tRNA --> Transfer RNA

bring aa over to growing peptide chain

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rRNA --> Ribosomal RNA

Structural element of ribosomes

target of many antibiotics

highly conserved---> used in bacterial identification

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Gene Expression

Very Fast Process in Bacteria b/c happens in Cytoplasm

(Slower in Eukaryotes bc start in nucleus)

DNA --> RNA Polymerase --> TRANSCRIPTION --> mRNA --> TRANSLATION--> Protein

*lots of drugs that work by stopping translation to prevent protein synthesis

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Bacterial Growth

Divide by Binary Fission

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Binary Fission

Makes Clones of each other

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Phases Of Growth

  1. Lag
  2. Logarithmic
  3. Stationary
  4. Death
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Lag Phase

getting ramped up and ready to go

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Logarithmic Phase

doubling over and over until run out of nutrients

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Stationary Phase

Just wait

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Growth Types

Vegetation State

Biofilms****

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Vegetation State

Free Flowing Bacteria

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Biofilms

** MOST COMMON **

colonies of bacteria that live in harmony

Stick to something --> IV Catheders + Prosthetics

bacteria growing rapidly on the outside + dormant on the inside

bacteria can talk to each other and express genes that can lead to antibiotic resistance

**intrinsically resistant to antibiotics**

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Vegetative Chart

Occurrence: Nutrients Plentiful

Impact of Enviro Conditions: Big Impact/ Die

Antimicrobial Resistance: Low Resistance

Growth: Rapid

Community Effects: None

Clinical Implications: Rapid Growth + Speed

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Biofilm Chart

Occurrence: Period of stress

Impact of Enviro Conditions: Reduced

Antimicrobial Resistance: Intrinsic

Growth: Moderate to Slow

Community Effects: Quorum Sensing

Clinical Implications: Resistance to antibiotics, adherence to prosthetic material

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Quorum Sensing

Talking to each other

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Obligate Aerobes

Need O2 to grow

ex. Tuberculosis, Molds (fungi) in lungs

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Obligate Anaerobes

Cannot tolerate oxygen

hard to culture

ex. Bacteroides, fusobacterium in gut

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Facultative Anaerobes

Prefer oxygen filled enviro but can grow w/o it

ex. E.coli, stapphoric, E.Faecalis

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Normal Flora

commensals

benefit from us w/o damaging us

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Resident Microbiota

relatively fixed

can re-establish if killed

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Transient Microbiota

colonize for period of time

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Function of Normal Flora

Bacterial Interference --> prevent colonization of pathogens

Nutrient Synthesis --> Vit. K

Can prevent chronic disease

Can cause disease in compromised patients

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C. Difficile Infection

Obligate, Spore forming anaerobe

treated w antibiotics ~30% success

treated w fecal transplant ~ 90% success

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When C.Diff treated w antibotics

antibiotics also destroy everything there

if treatment fails, more likely to fail again

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Colonization

Presence of Organisms w/o Infection

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How To Treat Patients W/ ID

  1. Suspect Infection
  2. Culture Suspected Sites (Begin Empiric Therapy)
  3. Stain Sample
  4. Identification
  5. Susceptibilities (What Drugs Will Work)
  6. Definitive Therapy
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Empiric Therapy

"best goes" treatment

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Definitive Therapy

Targeted for that patients exact strain