introduction to bacteriology Flashcards
what are the 3 domains of life?
bacteria
archaea
eukarya
when did prokaryotes come to be? eukaryotes
prokaryotes
around 4-3.5 billion years ago
eukaryotes
around 2-1.5 billion years ago
what’s unique about archaea (in comparison to bacteria)?
can live in extreme environments
don’t cause human diseases (they are not pathogenic)
what are prokaryotes?
the smallest, simplest, and most abundant cells on Earth
includes bacteria and archaea
lacks a nucleus and other complex organelles
— they have no membrane bound organelles
describe the 4 phases of growth bacteria undergo
LAG
- cellular activity
—- cells increase in size, but no cell division
—- bacteria “re-wires” metabolism
LOGARITHMIC GROWTH
- cell divides by binary fission and doubles in numbers after each generation time
- high metabolic activity because DNA, RNA, cell wall components, and other substances necessary for growth are generated by division
- appears like a steep incline
STATIONARY
- population growth starts to decline because of depletion of available nutrients and accumulation of waste products
—- increased competition for nutrients and cells become less metabolically active
—- in this phase, spore forming bacteria produces endospores and pathogenic bacteria produce virulence factors that help them survive harsh conditions and cause disease
- appears like a plateau on the graph, no overall population growth
DEATH
- as nutrients become less available and waste increases, number of dying cells rises
- as dying cells lyse, they spill their contents into the environment, making these nutrients available to other bacteria
- appears as a sharp decline
what are endospores?
highly differentiated cell that is formed within a vegetative or mother cell. the vegetative cell is mainly referred to as a sporangium.
they are highly resistant to heat, desiccation, radiation, chemicals, and some disinfectants
ensures the survival of a bacteria during harsh environmental conditions e.g. overpopulation, nutrient deficiency, or unfavorable climatic conditions
a “dormant” stage of the life cycle
most common in soil
endospores of bacillus and clostridium genera are the best studied
which bacteria can form endospores?
only gram+ and only a few can do it
what are virulence factors?
bacteria-associated molecules that are required for a bacterium to cause disease while infecting eukaryotic hosts such as humans
produced by the pathogen
what is generation time aka doubling time?
time it takes for one generation to divide into daughter cells
varies for species - some grow fast (e.g. DT = 10 minutes) or slow (e.g. DT = 24 hours)
what are the 3 types of bacterial shapes?
bacillus
- rod shaped
coccus
- spherical
spirillum
- spiral-shaped or curved
what is bacillus?
bacteria that are rod shaped
what is coccus?
bacteria that are spherical
what is spirillum?
bacteria that are spiral-shaped or curved
what are obligate aerobes?
requires oxygen for growth
what are obligate anaerobes?
oxygen is toxic for growth
what are facultative anaerobes?
can use oxygen if present, but can also growth without oxygen
what are aerotolerant anaerobes?
don’t use oxygen – but oxygen isn’t toxic!
what are microaerophiles?
grows best with low levels of oxygen
in order, what’s the taxonomic ranks for classifying bacteria
Donkey Kong Picks Cheese Over Family, Gains Super Strength
domain
kingdom
phylum
class
order
family
genus – should be capitalized and italicized
species – should be italicized
strain (diversity within species!)
among bacterial species, what’s notorious for their diversity? how diverse is this specie?
E COLI
only 60% of it is identical to other E coli
(humans 99.5% identical with each other!)
why is there diversity within bacterial species?
due to bacteria’ short life cycle, high reproduction rate, and ability to adapt to environmental changes
who developed the staining technique?
Hans Christian Gram
what are the staining colours of the 2 major types of bacteria?
gram+
—- purple (bc more dense with peptidoglycan)
gram -
—- pink (bc less dense with peptidoglycan)
what happens when gram staining is conducted on mycobacteria? why?
appears neutral - neither positive nor negative
due to thick, waxy cell wall that resists destaining/decolourization with the acid and alcohols used in gram staining – ability called acid fast and is found in mycobacteria
but it’s actually gram +
what is acid-fast?
a physical property of certain bacteria and cells that allows them to resist decolorization by acids during laboratory staining
— a thick, waxy cell wall
what are mycoplasmas?
small, spherical, self-replicating bacteria
they have a plasma membrane, ribosomes, and a genome – but no cell wall
gram-
differentiate between mycobacteria and mycoplasmas?
mycoplasma has no cell wall and thus, no distinct shape
describe the process of staining – note the colour at each stage
- flood the heat-fixed smear with crystal violet for 1 minute
—- all cells become purple - add iodine solution for 1 minute
—- all cells remain purple - decolourize with alcohol briefly - about 20 minutes
—- gram+ cells are purple; gram- cells are colourless - counterstain with safranin for 1-2 minutes
—- gram+ cells are purple; gram- cells are pink/red
what’s the purpose of counter staining in the staining process?
to help differentiate the cell types
before this step, gram+ cells are purple and gram- cells are colourless
adding safranin, a pink stain, stains gram-, making it pink. has no visible effects because gram +’s purple colour is much darker
describe the structure of bacterial cell walls
rigid structure prevents osmotic lysis
contains peptidoglycan
— larger amounts in gram+
— glycan backbone which is made up of alternate, repeating N-acetylglucosamine (G) and N-acetylmuramic (M) disaccharide units
—— cross-linkages between M sugars
since it’s not found in eukaryotes, it’s a common target of antibiotics
what component of most bacteria prevents osmotic lysis?
their cell wall
differentiate between gram+ and gram- bacterial cell wall
gram- organisms have less extensive cross-linking in their peptidoglycan layer, making it LESS RIGID
gram - has a thinner peptidoglycan layer and has an outer membrane in addition to the cytoplasmic membrane present in all bacteria. the space between the outer membrane and the inner cytoplasmic membrane is called the periplasm space.
on it’s outer membrane, is a a layer of lipopolysaccharides (endotoxins)
what makes up the glycan backbone of peptidoglycan in bacterial cell walls
alternate, repeating N-acetylglucosamine (G) and N-acetylmuramic (M) disaccharide units
what is the periplasm space?
the space between the outer membrane and the inner cytoplasmic membrane in gram- bacteria
what are lipopolysaccharides?
found on the outer membrane of gram- bacteria
part of it is endotoxin, toxic substances that can cause inflammation and fever
what are the components of the lipopolysaccharide? describe them
O-specific polysaccharide aka O-antigen
- found at the end
- antigenic and highly variable (different bacteria makes different O-antigens)
- plays a role in colonization, resistance to the immune system, and virulence
core polysaccharide
- links the O-antigen to the lipid A
lipid A
- disaccharide and fatty acid group
- recognized by the innate immune system – if they over-respond, it can lead to a cytokine storm which then results in septic shock!
- it’s the endotoxic part
- hydrophobic, how it’s able to attach to the membrane
describe nucleoids and its genetic material
where genetic material is found in prokaryotes
like other organelles in prokaryotes, it had no membrane
it’s genetic material is generally in the form of single, circular chromosomes – some bacteria will have multiple, linear chromosomes
haploid genome like in all prokaryotes!
– one set of chromosomes
– allows bacteria to evolve very fast since favourable mutations are chosen easily
what are plasmids
extra-chromosomal genetic elements
usually, not required for bacterial growth
often encode for ‘fitness’ factors – e.g. antibiotic resistance
can be transferred from bacteria to bacteria (horizontal gene transfer)
– transferring antibiotic resistance – leading to superbugs
describe the human microbiota (– where can bacteria be found in humans? where can it not?)
surface tissues have extensive populations of microbes
internal organs are usually sterile - but bacteria can some times be found here
the collective “genome” of the human microbiota contains more than 100 times as many genes as our genome
what is commensalism?
a relationship where one benefits without helping or hurting the other
what is mutualism?
a relationship where both benefits
what is parasitism?
a relationship where one benefits at the expense of the other
the microbe/pathogen is generally the one benefitting from the host
– parasites are usually eukaryotes!
what does a bacterial pathogen need to do to be successful?
colonization
invasion/toxicity
immune evasion
- nearly all pathogens have mechanisms to evade the immune system
transmission
what are some virulence factors of bacteria?
SURFACE
– lipopolysaccharides (LPS) aka endotoxins
– flagella
– pili and adhesions
– capsules
– secretion systems (complexes that allow bacteria to secrete stuff)
SECRETED
– exotoxins
what are pili and adhesions?
surface structures involved in attachment to surfaces, host tissues, other bacteria
pili are similar to fimbriae, both attach to things
plaque is loaded with many bacterial species – the pili helps them stick to teeth and gums
what’s a flagella?
structure that allows some bacteria to be motile
uses chemotaxis
it can run (smooth movement) via counterclockwise rotation and tumble (bumpy movement) via clockwise rotation
what’s a capsule?
usually made of exopolysaccharides
attachment to host tissues
protection from host immune system
can sometimes be used in vaccines
important for formation of biofilms, slimy, glue-like substance
what are exotoxins?
soluble proteins excreted by bacteria that can damage host
—- hallmark of a toxin-mediated disease
some exotoxins (inactivated) can be used as vaccines
– e.g. tetanus
what are the classes of exotoxins?
hemolysis
- destroys RBCs (not WBCs)
toxins that function inside host cells
- e.g. E.Coli, diphtheria
extracellular enzymes
- destroys tissues (e.g. proteases)
superantigens
- turns on adaptive immune system
describe bacterial intracellular pathogens
taken up and survive within phagocytic cells
– e.g. macrophages
some ‘force’ their own uptake into epithelial cells
allows bacteria to hide from different components of the immune system
what are stages of biofilms?
attachment
- initial contact between bacteria and surface
microcolony development
- begins to grow exopolysaccharide
biofilm development
- bacteria begins growing very slowly and becomes very resistant to antibiotic treatments
maturation
- tip of film: releases bacteria to complete biofilm life cycle (attach to new surface)
dissolution/dispersal
what are biofilms?
in nature, most bacteria live on biofilm structures (e.g. teeth)
organized structures/channels for nutrients to enter & waste products to exit
– the real problem implanted devices (e.g. urinal stint) develop infections very quickly & cannot be killed w/ antibiotics → must remove & replace it
what type of bacteria is more resistant?
gram - is more resistant than gram +
what are superbugs?
bacteria, fungi, or other microorganisms that are resistant to many antibiotics and other drugs used to treat infections
how are most commensals actually mutualistic?
no intention of helping the other, but helps as a byproduct e.g. bacteria in human gut!
what type of bacteria can’t be visualized well using the gram stain technique?
mycobacteria - acid fast
mycoplasma - no cell wall
