week 2 material Flashcards
what are 2 ways to define MICROBIOLOGY?
- by the organism we’re studying
- the mechanism we’re using to look at the organism
what does acellular mean?
organism can NOT replicate on its own/ does not contain cells
they do have genetic material and proteins
what are 2 acellular agents that transmit and cause disease ?
virus + prions
they are not free-living
what is aseptic technique?
a method used to look at species and doesn’t contaminate other species
why is it called microbiology?
you can only see the organism with the help of a microscope
what microbes represent all 3 domains of life?
Bacteria = single-celled microorganisms
Eucarya = multicellular organisms (plants, animals, fungi and protists)
Archaea = single-celled microorganisms that can survive in all types of environments
How did people used to think diseases were spread?
MIASMA THEORY
that diseases were caused by bad air/harmful vapor and rotten food/organic material
this led to clean cities, better sanitation and the building of better drainage systems
what did Antoni Van Leeuwenhoek discover?
he made and used microscopes
he found animacules in pond water
- single-celled protozoa/eukaryotes
- fungi
- algae
- tiny animals
now known as microorganisms
what were some indirect evidence that MICROBES cause disease
JOSEPH LISTER
- surgeon
- thought disease was caused by pollen-like dust
- incorporated disinfection -> increased survival post-op + decreased post-op infections
- disinfection = use of phenol to disinfect skin and instruments
ROBERT KOCH
- looked at the bacterium BACILLUS ANTHRACIS
- was observing mice and how they got sick
EXPERIMENT
- took the tissue of an infected mouse and inserted it into a healthy mouse
- took the spleen (organ) of infected mouse and passed it through 20 mice
- took spleen from mouse #20 who HAD SYMPTOMS OF ANTHRAX and made a broth culture
- isolated bacillus anthracis from the culture
what were Robert Koch’s 4 postulates (statements that he claimed to be true without any evidence) and why may they not be true
- the suspected agent had to be present in all infected individuals
- the agent has to be isolated + grown in pure culture (it’s only the one agent in the culture)
- the cultured agent will cause the disease once injected into a healthy and susceptible host
- the agent that was injected into the host can then be reisolated
why might Koch’s postulates not be true?
PATHOGENS ARE ONLY FOUND IN DISEASED INDIVIDUALS
- people can have the agent but also not develop the disease - depends on the host’s susceptability
ALL HEALTHY TEST SUBJECTS ARE EQUALLY SUSCEPTIBLE TO DISEASE
- subjects have different susceptibility and different reasons/causes/factors that allow them to have that disease
- can be based on their immune system in that moment
ALL PATHOGENS CAN GROW IN A PURE CULTURE
- some can’t be cultured in labs
- some microbes can NOT grow on their own or are intracellular organisms and can only grow with the help of a cell
ANIMALS CAN SERVE AS A RELIABLE MODEL FOR HUMAN DISEASES
- some diseases only affect people
- injecting people with human-specific diseases are not ethical
PATHOGENS CAUSE THE SAME DISEASE PRESENTATIONS
- a pathogen can cause more than 1 presentation (can be shown in someone in different ways)
- diseases can have multiple causes
what was the update to Koch’s postulates
it included molecular tests to see if the pathogen or the gene that caused for the organism to be pathogenic was present
the molecular tests help to see if the organism is intracellular/can’t grow or if it can be present in harmless + pathogenic strain
- helps to see if the organism is intracellular and can’t grow or if it’s a harmless pathogen ??
what are the groups of microbes?
- viruses
- bacteria
- fungi
- parasites (protozoa, helminths - worms)
what is bacteria
- prokaryotes (unicellular)
- makes yogurt, cheese
- there can be bad and good bacteria (can keep intestines happy or cause food poisoning and infectious diseases)
what are viruses
- depends on host cells to survive and replicate
- can infect bacteria (ex. bacteriophage)
- causes infectious diseases (severe)
- different shapes
what is fungi
- sizes vary
- different shapes - can be single-cells or multicellular
- eukaryotic
- heterotrophic - relies on organic material for food
- important for decomposition and fermentation
- causes a range of diseases
what are parasites?
- sizes vary
- different shapes - can be unicellular or multicellular
- eukaryotic
- relies on host to survive
- can have multiple hosts + has complicated lifecycles
- causes a range of diseases (mild-severe)
- usually a protozoan (unicellular eukaryotes) or worm
what were semmelweis’ initial observations?
there had been a lot of deaths among his patients
division I had a higher mortality rate and it was run by male medical students and doctors
division II had a lower mortality rate and it was run by female midwifery students
what is infectious disease
growth of a microbe or the microbe’s products causes damage to the host
what is a pathogen and examples of a pathogen
a microbe that can cause a infectious disease
= virus, bacteria, fungi, protozoa, prion, or worm
what are the steps for a pathogen to cause an infectious disease?
there are 7 steps
1. maintain a reservoir
2. has to be transported and enter a host
3. adhere, colonize, and/or invade host cells/tissues
4. evades/fights against the host’s defenses
5. multiples and completes its life cycle
6. mechanically or chemically damages the host
7. leave the host and returns to its reservoir or finds a new host
what does it mean for a pathogen to maintain a reservoir?
it’s present/circulates in low concentrations in susceptible hosts or in water
it also maintains population in a non-susceptible host
how does a pathogen get transported and enter a host?
through direct contact
- fecal-oral
- droplets
- aerosols
- sexual contact
through indirect contact
- fomites (inanimate objects that can house pathogens)
through vectors
- insect vectors (malaria parasite - the pathogen that carries the agent to the host)
what are some routes of entry for pathogens
- eye
- nose
- mouth
- ear
- placenta
- vagina
- anus
- urethra
- insect bite
- needle
- broken skin
what does it mean for the pathogen to colonize or invade host cells/tissues
pathogens can attach to their hosts
- viruses = has specific receptors/glycoproteins to enter the host
- bacteria = has adhesion molecules to attach to tissues
pathogens can enter their host/host cells
- not ALL pathogens can enter host cells
- ALL VIRUSES CAN
- TB, malaria, and salmonella CAN
how do pathogens move into the host?
they can attach to the host using ATTACHMENT PROTEINS
- found on viruses and bacteria
- the ligands of viruses and bacteria bind to the host cell’s receptors - this determines host cell specificity (b/ the ligand is specific for the specific receptor on the host cell)
- bacterial pathogens attach to each other to create a BIOFILM
what causes for the prevention of an infection?
changing or blocking the ligand or its corresponding receptor
the pathogen isn’t able to make attachment proteins making the pathogen not virulent
what does a pathogen do to fight against the host’s defenses
it forms a CAPSULE
- bacteria has a polysaccharide coat - prevents it from being digested by host WBC
!! pathogens that do NOT have capsules - are NOT virulent
it reproduces inside of the host cell
changes it’s surface antigens to blend in with the host cells
How do viruses, bacteria, and protozoa multiply/reproduce
VIRUS
- takes over the host cell’s system to create a new virus
BACTERIA
- binary fission
PROTOZOA
- asexually or sexually
how does the pathogen mechanically or chemically damage the host?
using toxigenicity - pathogens can create enzymes that then create toxins - exotoxins and endotoxins
EXOTOXINS = small protein toxins that damage the host
ENDOTOXINS = components of the bacterial cell wall trigger a strong immune response that damage the host
the toxins is what brings on the immune response
what is microbiota
a population of microbes that are in a area of an individual (example: GI tract)
the microbiota can be different across different sites of the body and can be different from person to person
changes in microbiota can influence health
what is a microbiome
all of the genomes and genes of a microbiota
what does it mean when microbes are colonized on host
microbes are present on the body but do not cause disease
this is due to the host’s diet, environment and genetic factors
what are benefits of normal microbiota
prevents bad bacteria from infecting/limits the opportunistic pathogen from colonizing and infecting
creates vitamins, essential amino acids + other metabolic co-factors
gives 10-15% of calories from food
helps to control digestion efficiency and control body weight/digests things that are hard to digest
what is dysbiosis
a change in the microbiota’s structure or function which creates a disruption in the homeostasis/balance between the microbial community and its host
what are the molecular aspects of bacteria?
bacteria is a prokaryote
- prokaryotes lack a nucleus
- prokaryotes have a single circular chromosome in a nucleoid
- prokaryotes are smaller than eukaryotes
- prokaryotes do not have membrane-bound organelles
- prokaryotes have plasmids (another form of genetic material)
what is vertical gene transfer
genes get passed from generation to generation
- bacteria has asexual reproduction
- doesn’t have genetic diversity b/ its the exact same DNA being passed down
what is horizontal gene transfer
genetic material gets transferred from one organism to another organism in the same generation
- specifically plasmid
- allows for genetic diversity
- genetic diversity is important for antibiotic resistance
what is the bacterial cell wall made out of and what does it do
one major component = peptidoglycan (protein + sugar)
- protects bacteria from harsh external environment
- targeted by antibiotics
what is the peptidoglycan composition for gram-positive bacteria and gram-negative bacteria
gram-positive = thick peptidoglycan
gram-negative = thin peptidoglycan + outer cell membrane
- it’s in between the cytoplasmic membrane and the outer cell membrane
what does a gram stain do and what are the stains for gram-positive and gram-negative bacteria
gram stain = stains organism based on the characteristics of its cell wall
gram-positive = stains purple
gram-negative = stains pink
what is the gram stain process
step 1: add crystal violet -> stains cells purple or blue
step 2: add iodine -> makes crystal violet less soluble and makes it stick to the cell wall better -> cells are still either purple or blue
step 3: add alcohol -> washes the stain away from the gram-negative cell wall -> GP remains blue or purple + GN are colourless
step 4: add safranin -> stains anything that is not stained with crystal violet, allows dye to stick to GN -> GP remains blue or purple + GN appears pink or red
how is bacteria identified and named
based on its shape, cell arrangement, and gram stain
the same shape can cause different diseases
same shape does not mean same properties
what are the bacteria shapes called
coccus
bacillus
vibrio
coccobacillus
spirillum
spirochete
what are the different arrangements of bacterial cells and which are the most common arrangements
single coccus
pair of cocci
4 cells arranged in a square
chain of cocci
cluster of cocci
chain and cluster is the most common arrangements
what are the characteristics of a bacteria causing disease
pathogenicity = when a microorganism is able to cause disease
virulence = the degree of pathogenicity/the severity of the disease
- this is based on case fatality rates + its ability to invade the tissues of the host
- the ability for the infectious agent to create pathological effects
what does bacteria have that increases its ability to cause disease
virulence factors - molecules or structures that increase this ability
what factors affect the outcome of host-pathogen interaction
- host’s health state
- depends on age (very young and very old being the most susceptible to the pathogen)
- its nutrition
- its state of immunosuppression (due to other diseases or drugs) - virulence of pathogen
- how infectious the pathogen is
- how invasive the pathogen is
- the toxigenicity of the pathogen
what are indicators of virulence
ID50 = median infectious dose = the amount of pathogen cells or virus particles needed to cause an active infection in 50% of vaccinated/inoculated animals
this dose does not correlate to the disease severity
LD50 = median lethal dose = the amount of pathogen cells or virus particles required to kill 50% of infected animals/hosts
can a bacteria be virulent without being pathogenic or causing disease
no
what are some virulence factors
extracellular enzymes
- secreted by pathogens
- dissolves structural chemicals
- helps pathogen maintain the infection, invade and avoid the body’s defence mechanism
toxins - endotoxin and exotoxin
- chemicals harm tissues
- chemicals that trigger the host’s immune response which causes damage
- bacterial capsule
- antiphagocytic chemicals
what is toxemia
toxins in the bloodstream that get carried from the site of infection to other areas of the body
what is endotoxin
part of the bacterial cell wall
released when cell dies
what is exotoxin
proteins that get secreted by bacteria
meant to target something
how does virulence factors prevent the pathogen from going through phagocytosis by the host cell’s phagocytic cells?
using bacterial capsules or antiphagocytic chemicals
bacterial capsules
- made up of chemicals that are not seen as foreign
- slippery making it hard for phagocytes to take in bacteria
antiphagocytic chemicals
- prevents the lysosome to merge with the phagocyte
- leukocidins specifically destroy phagocytic WBC directly
what are mechanisms that allow for the bacteria to survive in harsh environments?
they create endospores and biofilms
what is endospore
it’s a structure that is tough, non-reproductive and inactive and allows for bacteria to survive in harsh environments
very resistant to heat-drying + chemicals
what are biofilms
structured communities of bacteria that are embedded into extracellular matrix
the community of bacteria sticks to the surface
protects the bacteria from environmental stresses + antimicrobial agents
where do biofilms form
on tissues -> wounds, airways, etc.
on foreign bodies -> prosthetic joint
does this to cause infections
list smallest to biggest: worms, bacteria, virus, protozoa
viruses
bacteria
protozoa
worms
