Microbio lecture 1 Flashcards
Initiation of infectious disease is known as what, and what happens after?
Colonization -> 1.) elimination of microbe , no effect on host
2.) infectious disease (tissue dmg from organism)
3.).transient/prolonged carrier state.
3 common shapes of typical bacteria and names
Name for no distinct shape
Bacillus: Rod
Coccus: sphere
spirillus: spiral
Pleomorphic = no shape
gram positive bacteria
Thick peptidoglycan layer
1 membrane
Gram negative bacteria
Contains LPS (Lipopolysaccharide). Synonymous with endotoxin.
thin peptidoglycan layer, between 2 membranes.
Fungi Characteristics
Eukaryotic
Some unicellular (yeasts) or multicellular (molds,mushrooms)
Reproduction asexual/sexual/both
Produce spores
Generally saprophytic (feed on dead/decaying matter)
Non-photosynthetic
Tend to target lungs
Medically important fungi : Infection site
Candida albicans: Vagina, mouth
Cryptococcus neoformans: Lungs, Meninges, Wound/Skin
Histoplasma capsulatum: Lungs
Aspergillus niger: Lungs
Blastomyces dermatitidis: Lungs
Protozoa characteristics
Eukaryotic
Unicellular
Non-photosynthetic
Many free living, but parasitic to humans
Can be intracellular / extracellular parasites in blood, urogenital region, intestine
Medically important protozoa
Giardia lamblia -> causes STD
Trichomoniasis vaginalis -> causes STD
Trypanosoma species
Leishmania species
Helminths Characteristics, and 3 main groups
Eukaryotic
Multicellular
Worms
Parasitic
3 Groups:
1.) Nematodes (Roundworms)
2.) Cestodes (Tapeworms)
3.) Trematodes (Flukes)
Most common Helminth in US, causes, Characteristics
Enterobius vermicularis (pinworm) is the most common helminth infection in USA
Causes anal itching
Characteristics:
Elongated
NON-SEGMENTED
Tapered at both ends
**HAVE A COMPLETE DIGESTIVE SYSTEM UNLIKE OTHERS*
Characteristics of Cestodes
Ribbon-like
Segmented
Absorb nutrients (lack digestive system)
Characteristics of Flukes
Flat
Leaf-like
Absorbs nutrients (lack digestive system)
Use freshwater snails as intermediate host
Viruses Characteristics
Obligate intracellular parasites
Cannot replicate without a host cell
Has no cellular structure
Contains DNA or RNA
Surrounded by protein coat (capsid)
May have envelope from cell membrane of host cell
Virus particle called virion
Human microbiome definition
The human microbiome is the total number and diversity of microbes in and on the human body.
Most common sites of body inhabited by normal microbiota
Gut (intestinal tract, has the most amount of microbiota)
Skin
Mouth (oral cavity)
Nose
Eye
Microbiota in the Skin
Staphylococcus epidermis (90% of skin aerobes)
- Can colonize plastic catheters and medical devices that penetrate the skin. (This is why you must clean area well when you puncture skin).
Staphylococcus aureus
- skin infections
Propionibacterium acnes
- anaerobic
- Major player in causing pimples, feed on sebum.
Microbiota in Mouth / Nose
Streptococcus mutans
- colonize the teeth / gingival tissue
- can travel from oral cavity to heart following dental surgery, colonize in damaged heart valves which leads to endocarditis (fatal).
Streptococcus pneumonia
- can cause pneumonia.
Microbiota in Intestinal tract
H. Pylori can survive enzyme of stomache. Urea -> ammonia (basic) cloud surrounds H. Pylori, neutralizing acid.
Gut microbiota has the largest number of bacteria and the greatest number of species compared to other areas of the body.
Beneficial functions of normal microbiota
Competition. Competes with pathogenic microbiota
Some produce antimicrobial substances
Can stimulate development of immune system in the young
Can make vitamins (e coli makes vit. k)
Harmful effects of normal microbiota
Displacement from normal site to abnormal site causes problems
Diminishing population bad due to competition importance
Ingested food substances converting to carcinogenic derivatives
Normal microbiota overgrow / become pathogenic
Opportunistic definition
Opportunistic - Some microbes cause disease only under certain conditions
All terms of Microbiota
Subclinical - no symptoms
Latent - potential to become active
Opportunistic
Primary - Can cause other disease manifestations
Secondary - Reactivation of latent infection/ second stage of infection
Mixed - 2 + bacteria infecting same tissue
** Pyogenic - pus forming
** Pyrogenic - fever / heat inducing
Fulminant - Infections occur suddenly and intensely
Bacterial pathogenesis (pathway)
1.) Entry
2.) Adhesion
3.) Invasion
4.) Propagation
5.) Damage
6.) Progression/Resolution
Virulence factors and how it is quantified by.
These are characteristics of a bacterium that enhance its pathogenicity
Can be quantified by
1.) Infection Dose (ID 50): How many organisms are required to cause disease in 50% of those exposed
2.) Lethal Dose (LD 50): How organisms kill 50% of test animals.
Target question:
What is the role of the capsule?
When an organism has a capsule on, it is harder for it to be phagocytized. (It is antiphagocytic)
Virulence factors
Capsule
Surface adhesion molecule
Bacterial enzymes (collagenase / hyaluronidase) These breakdown ECM.
Iron binding proteins
Bacterial toxins.
Bacterial toxins
Exotoxins: Secreted. More toxic. (remember, lipopolysaccharide LPS used synonymously with exotoxins).
Endotoxins: not secreted, but can be released by bacterial lysis.
Host-mediated pathogenesis
Pathogenesis caused by host response rather than the bacterial factors.
Classic Question: Inflammatory cytokines are an example. Host immune response is so intense that host tissues are destroyed.
Viral infections can lead to:
Cell death
Transformation (Normal cell -> cancer cell) Example: HPV
Cell fusion (large giant cells)
Cytopathic effect (Visible changes, cell disintegration)
Symptoms and Indication for physical examinations
Bullseye skin lesion: Lyme disease
Chills, Fever, cardiovascular instability: Bacteremia
Pulmonary consolidation (fluid in lung): Pneumonia
Stupor (near unconsciousness) / stiff neck: Meninges
Common techniques: Gram stain
Trying to differentiate between gram positive / negative organisms.
CIAS : Crystal violet, iodine, acetone, safranin solution. Do this in order.
1.) Add first stain, crystal violet.
2.) Use iodine to trap stain. Fix it.
3.) Acetone decolorizes sample. Wash it out.
4.) If gram positive, crystal violet will be trapped. Will be purple.
5.) If gram negative, will be pink. (thin peptidoglycan layer, so the Crystal violet washes out).
Acid-fast stain
Purpose: try to find mycobacterium. These contain large amounts of mycolic acids (FAs)
When cell wall has a lot of fatty acids, gram stain does not work well.
Stain pink when positive. Negative = blue.
India Ink
Look for capsule. Stains background so capsule is visible.
Oxygen requirement terminologies
Obligate aerobes: requires oxygen for growth
Obligate anaerobes: requires anaerobic environment for growth
Facultative anaerobes: have ability to grow anaerobically, but better with oxygen
Aerotolerant anaerobes: Do not use oxygen but can tolerate it.
Microaerophiles: Requires oxygen concentrations lower than O2 found in
air.
Solid / liquid medium
Solid medium : nutrient agar. Used for isolation of bacterium
Liquid medium : nutrient broth. Used to grow larger quantities of bacteria.
Types of media : Characteristics
Defined : Contains known quantities
Undefined: Unknown quantities
Enriched: Support wide growth of organisms. *** Examples: Blood agar, chocolate agar.
Selective: growth of selected microorganisms
Differential: Differentiate organisms
Reducing: Growth of obligate anaerobes.
Catalase Test
Enzyme that degrades hydrogen peroxide. Looking to see if it has catalase.
U just add h2o2. If it bubbles its positive. (cuz h2o and o2 released)
**staphylococci = positive
**streptococci = negative
Oxidase Test
Looking to see if it has cytochrome c oxidase. (complex 4 of ETC). If you have this, oxidation occurs.
Coagulase Test
Clot formation = positive test result.
Used to differentiate staphylococcus aureus (positive) from other staphylococci (negative).
Urease test
Expose urea. urea broken down to ammonia. check pH levels. (alkaline side)
Quelling reaction
Looking for organisms with capsules.
Latex Agglutination Test
Unknown antigen exposure to bound antibody (or other way around) Agglutination occurs.
Complement fixation
Detect patient’s serum antibody by the ability of the antibody to bind complement.
Solution pink if negative.
ELISA
Direct assay: one primary antibody conjugate.
Indirect Assay: Using 2 antibody conjugates.
Fluorescent Antibody Test
No fluorescence = no virus present
Fluorescence = virus present
Nucleic Acid-based techniques (NAT) (NAAT)
Detect / amplify nucleic acid of pathogen
Susceptibility Tests
Do this when you don’t know which antibiotic to use. DO this when you want to know which one is affected.
