Week 2 Flashcards
How is microbiology defined
-by organisms studied
Or
-by the techniques used
What types of organisms are studied in microbiology
Microscopic
-bacteria
-viruses
-yeasts (fungi)
-protozoans
Macroscopic
-worms
-moulds (fungi)
Before germ theory people thought disease was spread through…
Miasma theory
-bad air/ harmful vapours carried disease
Who is Antoni van Leeuwenhoek
-Dutch
-made simple microscopes
-examined water and saw fungi, algae, and single cell protozoa which he called animacules
-these were later called microorganisms
Who is Joseph lister
-British surgeon
-believed sepsis was caused from pollen like dust
-used disinfectant to improve survival after surgery
-disinfect skin and surgical tools
What are the 4 of Koch’s postulates
- Suspected agent must be present in every case of the disease
- The agent must be isolated and grown in a pure culture
- The cultured agent must cause disease in a healthy experimental host
- The same agent must be resonated from the experimental host
What are some faulty assumptions of Koch’s postulates
- pathogens are only found in diseased individuals
- all healthy subjects are equally susceptible to disease
- all pathogens can be grown in a pure culture
- animals are reliable human model
- pathogens tend to cause same disease presentations
What are the molecular Koch’s postulates
- The phenotype should be associated only with pathogenic strains of a species
- Inactivation of suspected genes associated with pathogenicity should result in measurable loss of pahogenicity
- Reactivation of gene should restore phenotype
List the microbes we are studying and their respective treatment
- viruses - antivirals
- bacteria - antibiotics
- fungi - antifungal
- parasites - antipatasitics
What are the two types of parasites
Protozoa and Helminths(worms)
Tell me about bacteria
-About 1um
- prokaryotes
- many are good some are bad
- make ought, cheese, and keep intestines happy
- food poisoning among other diseases
Tell me about viruses
- 10-100 nm
- many shapes
- acellular
- rely on host cell for survival/replication
- can infect bacteria (bacteriophage)
- many serious infectious diseases
Tell me about fungi
- many different sizes from a few um to several cm
- different shapes (single cell yeasts or multicellular molds)
- Eukaryotic
- Heterotrophic: dependent on organic matter for nutrition
- important for decomposition and fermentation
- many diseases
Tell me about parasites
-Size varies
- different shapes (unicellular Protozoa or multicellular helminths)
- eukaryotic
- often rely on host for survival
- often complex lifecycles, may have multiple hosts
- cause many mild and severe diseases
Tell me about Ignaz Semmelweis
-Hungarian doctor
-noticed larger death rate where physicians and med students assisted with birth compared to the midwife ward
-friend got what appeared to be childbed fever after getting cut during autopsy
-believed something was transmitted which caused the illness
-made doctors wash hands before childbirth
- deaths went down
Pathogen
A microbe that can cause an infectious disease
Steps for a pathogen to cause an ID
- Maintain a reservoir
- Be transported to and enter host
- Adhere to, colonize, and/or invade host cells or tissue
- Initially evade host defenses
- Multiply and complete life cycle
- Mechanically or chemically damage host
- Leave host and return to reservoir or new host
What does it mean for a pathogen to maintain a reservoir
To circulate at low levels in a susceptible host like influenza
Or to maintain population in a non-susceptible host (a zoonotic host for example)
Ticks are hosts for
Lyme disease and Rocky Mountain fever
Bats are hosts for
Rabies, Ebola, nipah, sars-cov
Rats are hosts for
Hanta virus
How can a pathogen be transported to and enter a host
Direct contact
- fecal-oral
- droplet
- aerosols
- sexual contact
Indirect contact
- Fomites: inanimate objects that can harbour pathogens
Vectors
- insect vectors
What are adhesins on bacteria
Molecules that help them attach to tissue
Do ALL pathogens enter cells
No
How do viruses enter their hosts
Specific receptors
Some bacteria pathogens attach to each other to form a…
Biofilm
Ways pathogens can evade host defenses
Capsules
- polysaccharide coat in bacteria which decreases probability of being eaten by immune cells
Reproducing inside host cells
Changing surface antigens to stay ahead of detection
How do viruses multiply
Hijacking cell machinery to produce new virus
How do bacteria multiply
Binary fission
How do Protozoa multiply
Both sexually and asexually
How do pathogens damage hosts
Toxins
The 2 types of toxins we know
Endo and exotoxin
What is an exotoxin
Small protein toxins which damage hosts and are actively released
What is an endotoxin
Part of bacterial cell wall which is generally released when the cell dies, elicits strong immune response which damages hosts
Reservoirs of IDs
Animal reservoirs
- zoonosis: disease spread from animal to human
- acquired from direct contact with animal, waste, or product. As well as blood sucking arthropods
Human carriers
-asymptomatic individuals
Nonliving reservoirs
- soil, water, food….
Is pathogenicity the rule or the exception for bacteria
The exception, we have many bacteria that live inside us and coexist and help, also tons of bacteria assist with food.
What is microbiota
Community of microbes in different sites of an individual
What is a microbiome
Aggregate of genomes and genes of microbiota
What is dysbiosis
Change in structural or functional configuration of the microbiota that disrupts homeostasis with host and microbial community and leads to adverse affects for host
What makes something a prokaryote
Lack of nucleus, single circular chromosome in nucleoid, smaller, usually lack membrane bound organelles, may have plasmids (extrachromosomal DNA)
How do bacteria transfer genes
Vertically: to the next generation through asexual reproduction
Horizontally: transferring genetic info to other organisms in the same generation through the use of plasmids.
What is the bacteria cell wall made of primarily
Peptidoglycan
What is peptidoglycan made of
Proteins(peptide) and sugars(glycan)
What is the difference between gram-negative and gram-positive cell walls
Gram positive have a thick peptidoglycan wall and gram negative have a thin peptidoglycan layer behind the outer cell membrane
Bacteria are often categorized based on what
The nature of their cell wall
Gram stains are what
A process which stains an organism based on the characteristics of their cell wall
A gram-negative bacteria will stain what colour after a gram stain
Pink or red
A gram-positive cell will stain what colour after a gram stain
Purple or blue
What are the different shapes of bacteria
Coccus, bacillus, vibrio, coccobacillus, spirillum, spirochete
Coccus has what shape
Sphere
Bacillus has what shape
Pill
Vibrio has what shape
Comma
Coccobacillus has what shape
Combination of spheres and rods
Spirillum and spirochete have what shape
Spirals
A single spherical bacteria would be called a
Coccus
A bacteria which looks like a pair of spheres would have the prefix followed by
Diplo- coccus
A bacteria which looks like a group of four spheres would be called a
Tetrad
A bacteria which looks like a chain of spheres would have the prefix followed by coccus
Strepto-
A bacteria which looks like a cluster of spheres would have the prefix followed by coccus
Staphylo-
what is pathogenicity
Ability of a microorganism to cause disease
What is virulence
The degree of pathogenicity
2 factors which affect the outcome of the host-pathogen interaction
State of host health
- age
- nutrition
- immune systems
Virulence of pathogen
- infectivity
- invasiveness
- toxigenicity
What is the ID50
Median infectious dose
- number of pathogen cells or visions required to cause active infection in 50% of “infected”
-is an indicator of virulence
What is the LD50
Median lethal dose
-number of pathogen cells or virions required to kill 50% of infected animals
Can a bacteria be virulent but not pathogenic
No since to be virulent you must be pathogenic
Can bacteria with low infectivity be virulent
Yes since virulence is just the degree of pathogenicity, it doesn’t need to be high just needs to be there
List some general virulence factors
Extracellular enzymes
Toxins
Factors which prevent phagocytosis
What are extracellular enzymes with examples
Secreted by pathogen
Dissolve structural chemicals in body
Eg
-hyaluronidase and collagenase
— break down epithelial cells and collagen
- coagulase and kinase
— form clot and dissolve clot
Toxins are
Chemicals that harm tissues or trigger immune response which causes damage
2 types exo and endotoxins
Toxemia
Toxemia refers to
Toxins in the bloodstream that are carried beyond the site of infection
Factors which prevent phagocytosis are
Bacterial capsules
- not recognized as foreign
- difficult to engulf
Antiphagocytic chemicals
-prevent fusion of lysosomes and phagocytic vesicles
-Leukocidins directly destroy phagocytes
What is an Endospore
A dormant tough non-reproductive structure which allows bacteria to survive harsh conditions
What are biofilms
Structured communities of microorganisms that are embedded in an extracellular matrix and adhere to a surface
-can form on tissues and foreign bodies
-allows bacteria to withstand environmental stresses and antimicrobial agents
