The Microbial World Flashcards
Koch’s Postulates
Koch first demonstrated that a microorganism causes disease (anthrax)
- The organism is regularly found in the lesions of the disease
- Isolated in pure culture
- When inoculated, culture should produce similar disease in experimental animals
- Organism should be able to be recovered from lesions in these animals
Discovery of Antiobiotic
Caused by unkempt lab
Left plates with bacteria on them, came back to find that mold was growing and the area around the mold did not have any bacteria
The mold secreted penicillin which inhibited growth of bacteria
Origins of Microbiology
1674: discovered microorganisms
1870: Germ theory
Cause contamination, cause disease
Late 1800s: Agents of diseases discovered; vaccination
Early 1900s: Viruses discovered; antiobiotics discovered
1900s: Threat of ID declines due to sanitation and hygiene, chlorination, antibiotics, vaccines, animal and pest control
Today: Re-emergence of IDs because we were treating patients with antibiotics (comeback diseases) and new diseases
Why are some diseases re-emerging?
- Increased globalization and trade
- Misuse of antibiotics
- Evolution of microorganisms
- Decline in public health (war zones)
- Inc in IC people (transplants, chemotherapy)
Prokaryotic vs. Eukaryotic
Divide by binary fission
Prokaryotic: (Bacteria!)
Small
Rigid peptidoglycan cell wall
Eukaryotic: Evolved from fusion of prokaryotic cells Membrane bound organelles No cell wall in animals Larger Nucleus and mito contain DNA
Sizes of Microorganisms and How we see them
Viruses < Bacteria < Protozoa and Fungi
Electron microscope < Light microscope < Human eye
Taxonomy
Escherichia coli
Genus, species
Definition of a species
Eukaryotes: Members can mate and have fertile offspring
Prokaryotes: Look at the 16S rRNA. If it is more than 97% different, they are not in the same species
Bacterial Shapes
Bacillus: rod Coccus: circular Streptococcus: chain Staphylococcus: clump Spirochete: snake-like; predestined to penetrate tissues Club shaped
Can also have appendages (flagella)
Spores: formed under bad environment as a way for the bacterium to stay alive (dry, nutrient deficient environment)
Capsule: Often anti-phagocytic; leads to more chronic infection that tends to disseminate further than if it were not capsular
Gram - membrane
Second outer membrane
Porins allow nutrients in and out of the cell
Thin peptidoglycan layer in periplasmic space
Outer leaflet has lipopolysaccharides linked to membrane by acyl chain
When washed with ethanol, can extract lipids and increase porosity, thus removing the crystal violet-iodine complex
Gram + membrane
Thick peptidoglycan layer
Permeability layer; Preventing loss of crystal violet-iodine, appearing purple
Gram Stain Test
- Fresh sample dried on plate
- Stained with crystal violet, all cells appear purple
- Add iodine, decreases solubility within cell, cells still appear purple
- Cells decolonized by washing with ethanol
* DIFFERENTIAL step*
Gram+ retain purple
Gram- do not (colorless) - Cells rinsed with counter stain safarin which stains Gram- PINK
Virulence
ID and LD (lethal)
ID50: number of microorganisms needed to infect 50% of host population
If you have a 10^5 bacteria and inject into ten mice, half will come infected
Virulence is opposite of ID
Ex. Shigella has a LOW ID, in the 10s. Takes a very small amount of organisms to infect 50% of hosts. Would be considered very virulent
Sterile areas in the body
- Lower respiratory tract
- Upper genitourinary tract
Intestine is LOADED with bacteria (large)
Skin has no Gram-
Lyme disease transmission
Zoonotic
Vector-borne
Reservoir is a mouse, transmitted to humans with the help of a tic
Preventive Measures
Standard: Hand hygiene, procedure appropriate
Contact: Gloves, gowns, private room
ex. diarrhea from norovirus or C. diff
Droplet precautions: If pathogens don’t travel more than 3 feet; masks/respirators, closed room
ex. influenza, N. meningitidis
Airborne precautions: Travel more than 3 feet; PARP respirators, airborne infection, All air leaving room going through HEPA filter
ex. Measles, Mycobacterium tuberculosis
Full barrier precautions: airborne + contact plus eye protection
ex. avian/pandemic influenza, SARS
Types of pathogens (3)
- Nonpathogens: present in microbiome; normal flora; occupy niches and prevent pathogens from coming in and causing the disease
- Opportunistic: present as normal flora; if it gets into the wrong tissues it can cause problems, or if it is given the opportunity of an IC patient
- Primary pathogens: if you see this in the sample, you know it is causing the disease
Immunizations common
Stages of Bacteria Pathogenesis
- Transmission
- Adhesion
- Colonization
- Spread
- Damage (directly- toxins or enzymes by bacterial products; indirectly- inflammation (immune responses))
- Evasion of host immunity (in host survival)
- Transmission to a new naive host
Virulence factors
Help bacteria invade the host, cause disease, evade host defenses
Some are targeted by vaccines and detected by specific tests
Adhesins: Allow bacteria to adhere to tissues
Invasins: Allow bacteria to get inside a host cell; evade humoral inflammation; now relying on cell-mediated inflammatory response to clear infection; nutrient rich cytoplasm and safe from host defense responses
Exotoxins: (Enterotoxins); secreted from a bacterial cell; bacteria mediated pathogenesis
Endotoxins: Released when cell is lysed; potent toxin that signals immune response; host mediated pathogenesis; GRAM- ONLY
Degradative enzymes: Break down tissues; allow bacteria to spread in tsisues
Adhesins
Allow bacteria to adhere to tissues
Pili (fimbriae) on E. coli
Protein adhesins: pull bacteria closer so they stick better to tissues and allow colonization
Biofilms: bacteria stick together and attach to a surface (plaque, catheter causes UTI)
Intracellular (bacterium growth)
Obligate: always need a host cell to replicate in
Facultative: can work intracellularly or extracellularly; life to replicate outside of the cell but then go into the cell to escape humoral immune responses and have access to more nutrients
Systemic disease (bacterial spread)
Vs. localized
Destruction of tissue barrier by tissue damaging enzymes
Penetration of cell membrane (invasion)
Types of Invasion of pathogens
- Passive uptake: immune cells that uptake bacteria (phagocytosis)
- Active invasion: Invasins on cell surface induce uptake by non-phagocytic cells; OR make virulence factors that allow them to invade non-phagocytic cells
Salmonella, Yersinia - Transcytosis: Intracellular motility by actin polymerization; go through cells
Shigella, Listeria
Syringe secretion systems
T3SS
Type 3 and 4 are syringe mechanisms
Multi-protein complex expressed by bacteria cell
Can inject effector proteins from bacterium into the cell
1. Mess with actin
2. Cleave rRNA, blocking protein synthesis, killing the cell
Make a complex stretching from bacteria cytosol into the host cell cytosol; effector proteins never encounter extracellular environment
Types of exotoxins
- Enzymes
Act on extracellular matrix
Collagenase, hyaluronidase
2. AB type toxins Two components (subunits) Cholera, diphtheria, shiga, pertussis, tetanus, anthrax, botulinum, E. coli heat labile toxin
- Membrane damaging toxins:
Phospholipases ex. Perfringens alpha toxin
Pore forming toxins ex. Listeriolysin
Cause hemolysis - Superantigens:
Enterotoxins of S. aureus
AB toxins
Intracellular acting toxin
B: Binds to cell surface receptor; determines host cell specificity of toxin; forms pore
A: disulfide bonds are broken and A becomes Active enzymatically and is transported to cell interior; toxic activity
Targets of A subunits:
1. ADP ribosylating toxins
Diptheria toxin: inactivates elongation factor (translation, protein synthesis)
Cholera toxin, pertussis: Activates adenylate cyclase (increasing cAMP levels)
- Others
Shiga, EHEC: cleaves rRNA (translation, protein synthesis)
Tetanus, botulinum: Blocks release of neurotransmitter
Examples of AB
- Shiga toxin
- E coli LT1
- Petussis toxin
Single A subunit with multiple B (A1B5)
*B subunit good target because it will affect all things downstream
Superantigens
Causes nonspecific binding of T cells
Produced by some pathogenic viruses and bacteria most likely as a defense mechanism against the immune system
Temporary interaction where the APC will just present the peptides of pathogens to the T lymphocyte
VERSUS SUPERANTIGEN which locks the presenting state APC to T lymphocyte
Endotoxin: LPS
Released by cell lysis, not secreted
Toxicity due to lipid A component (fatty acids, disaccharide, diphosphate)
Also has O-antigen component
Causes septic shock
Binds to LPS binding protein and interacts with host receptor CD14
Signals through toll-like recepor
How do pathogens evade host immune responses?
- Defensive
Capsule: protects from being phagocytksed
Serum resistance due to modification of LPS preventing C5b-9 complex - Offensive
Produce toxins which degrade immune components (C5a, IgA proteases)
Killing of phagocytes - Stealth
Antigenic variation
Antigenic variation
- A pathogen expresses an immunodominant surface antigen (largely recognized by immune system)
- Shut down expression of antigen and start expressing another type of antigen unrecognizable by antibodies
- Bacteria buys itself time to replicate until host develops a new set of antibodies that will recognize the new coat and try to kill the cells
Iron acquisition
Most bacteria need iron for growth
-bactin
Bacteria produce siderophores which bind to iron and then bind to a receptor on the bacteria to be taken up
Main way to acquire iron for growth
Virulence factors are encoded on:
- Chromosome: stable
- Pathogenicity island: Region of DNA that has all the genes coding for a specific set of virulence genes (ex. all components of T3SS: effector proteins and needle
- Plasmid: dispensable, can be transferred to another bacteria; extrachromosomal smaller DNA replicon
- Bacteriophage: spread DNA between bacteria (transduction) - bacterial viruses
- Transposon: highly motile; can accelerate spread of genetic material
Complentation
Reintroduction of a functional gene into mutant bacterium should restore the invasive wild type if the mutant is responsible
Type I toxin
Bypass cell membranes by activating signaling molecules on the cell surface
Type II
Directly attack the host cell membrane resulting in increased permeability
