bacterial structure I and II - notes and lecture Flashcards
why are bacteria readily visible in large numbers?
they make a turbid suspension
what is aseptic technique?
laboratory technique that allows the manipulation of sterilized material without bacteriological contamination
how are pure cultures made today?
(means culture with only one species of bacteria present)
prepared on medium solidified with agar - mixed bacterial suspension spread on the agar to yield isolated individual bacterial cells which grow into colonies
what determines bacterial taxinomy?
DNA sequence homology
determine using PCR
what are the most important bacterial characteristics for routine laboratory diagnosis?
1: morphology of colonies on appropriate agar medium
2: microscopic morphology and staining of individual bacteria
3: simple biochemical characteristics such as the ability to ferment a given carbohydrate
4: specific antigens detected by known antisera
what are Koch’s postulates? what are they used to determine?
used to establish the bacterial etiology of infectious diseases
postulates=
a: find the bacteria in all cases of disease
b: grow the bacteria in pure cultures
c: reproduce the disease in animals using the pure culture
d: reisolate the bacteria in pure culture from the experimental infection
note that some infectious pathogens won’t meet all of these but are still the agent responsible for the disease
what are koch’s molecular postulates used for? what are they?
used to define the molecular basis by which a specific infectious disease is caused
postulates =
a: phenotype under investigation should be associated significantly more often with a pathogenic organism than with a nonpathogenic member or strain
b: specific inactivation of a gene (or genes) associated with the suspected virulence trait should lead to a measurable decrease in virulence
c: restoration of full pathogenicity should accompany replacement of the mutated gene with the wild type original
what are the “higher” microorganisms?
in the eukarya domain: fungi, protozoa, algae
what does eukaryotic mean?
true nucleus
what are the “lower” microorganisms?
bacteria - bacterial domain - prokaryotic cells
what are the chromosomal characteristics of eukaryotic versus prokaryotic cells?
in eukaryotic cells, each cell has a number of different linear chromosomes within the nuclear membrane
in prokaryotic cells, each cell generally contains one circular chromosome that is not bound by a nuclear membrane
what are the differences in reproduction between eukaryotic and prokaryotic cells?
eukaryotic cells undergo mitosis, whereas prokaryotic cells undergo binary fusion
what are the differences in mitochondria between eukaryotic and prokaryotic cells?
eukaryotic cells have mitochondria with oxidative enzymes that carry out oxidative phosphorylation
prokaryotic cells don’t have mitochondria - rather, their oxidative membranes are associated with the cytoplasmic membrane o the cell
what is the difference in membrane bound structures between prokaryotes and eukaryotes?
eukaryotes have many membrane-bound structures including vacuoles, peroxisomes, etc. whereas prokaryotes have no membrane bound structures within the cell (with a few exceptions)
what are the differences between mechanism of movement between eukaryotes and prokaryotes?
eukaryotes move by cytoplasmic streaming of by contraction of flagella or cilia
prokaryotes don’t do cytoplasmic streaming or amoeboid movement, some have flagella
how are prokaryotic flagella different from eukaryotic flagella?
prokaryotic flagella are composed of a long helical filament composed of repeating protein subunits with a hollow tube down the middle
no microtubules and typically no membrane coat
what is unique about the cytoplasm of bacteria?
it’s usually very dense due to high content of ribosomes necessary for rapid growth
how do the cell walls in eukaryotic and prokaryotic organisms differ?
animal cells don’t have cell walls
higher plants and green algae have wall of polysaccharide cellulose
fungi cell wall of chitin
in prokaryotes wall composed of peptidoglycan polymer with muramic acid, D-AA and other components
what are the differences in RNA transcription and translation in eukaryotes and prokaryotes?
in eukaryotes, rna is transcribed in nucleus, spliced, transported to ER for translation
in prokaryotes nascent RNA is translated as it’s transcribed - no RNA splicing
what are the groups of prokaryotic cells? (2)
bacteria and archaea
those of medical importance are all bacteria
how do prokaryotic and eukaryotic cells differ in chemical composition? (sterols and muramic acid)
prokaryotic cells don’t have sterols (except for mycoplasma, which may) whereas eukaryotic cells do
most prokaryotic cells have muramic acid whereas eukaryotic cells don’t
what is the general diameter of coccus?
.8 to 1.0 um
how can the shape of bacillus vary?
rod can be long and slender or short and thick
ends of rod can be square, rounded, or tapered
what is different about the cell wall in spirochetes?
not rigid so they’re classified differently from rod or spheres
how does binary fission occur?
formation and subsequent joining of a central transverse wall
what can happen if daughter cells do not separate in binary fission?
get many-celled aggregates = filaments
more commonly occurs among the cocci
what determines the form of aggregates formed in binary fission?
the pattern of successive division:
a: successive divisions of cocci along the same axis result in chain (streptococci)
b: successive divisions that take place at right angles create tetrads or extensive flat plates of cells
c: three successive divisions at right angles to one another result in cuboid
d: get irregular clusters if successive divisions of cocci occur in any direction
in rod-shaped bacteria, division always takes place at right angles to the long axis so can only form chains
except in corynebacterium where rods stick together at ends so that get stack of rods or variety of groupings
describe the chemical composition of the cytoplasmic membrane of bacterial cells. (lipids)
similar to that of mammalian cells
20-30% lipid, 60% protein
phospholipid bilayer
describe the permeability of bacterial membranes
semi-permeable - if put in hypertonic media, contracts
water freely permeable but ions and non-ionized molecules larger than glycerol penetrate slowly except by transporters
what is a protoplast and how is it formed?
stable form of bacteria once cell wall has been digested
rod-shaped bacteria will assume spherical shape
cells will now burst if placed in hypotonic media because cell wall absent
what are the functions of the cytoplasmic membrane in bacteria?
1: contains oxidative enzymes - resembles inner membrane of mitochondria in both structure and function
2: contains enzymes which function in external cell wall synthesis
3: can pump nutrients from dilute external media
4: mechanisms for secreting toxins and certain enzyme
what components of bacterial cells would you see in the cytoplasm in EM? (list)
ribosomes
cytoplasmic granules
how do bacterial ribosomes compare with mammalian?
bacterial are smaller = 70S
mammalian are 80S except for mitochondrial, which are 70S
what are cytoplasmic granules?
storage bodies formed in bacteria under conditions where excess food is available
can be high molecular weight lipid or glycogen or metachromatic granules = polymerized phosphate (stains deeply with basic dyes)
how would you identify diphteria microscopically?
have metachromatic granules that will stain deeply with basic dyes
why are cytoplasmic granules important?
allow for storage of nutrients in large quantities without increasing osmolarity of the cytoplasm
what is the size of the cell wall in bacteria?
makes up approximately 20-35% of cell weight
what molecules are contained in all bacterial cell walls?
polymer of NAG linked to muramic acid by a glycosidic bond
short peptide consisting of 4 AA is linked to the lactic acid residue (these AA can vary across species)
what is muramic acid made of?
NAG linked to lactic acid
what creates the cross-linking in bacterial cell walls?
bonding between AA side chains - gives strength and rigidity to wall
through peptide bridge from terminal carboxyl of tetrapeptide to a neighboring amino or carboxyl group on another tetrapeptide chain (variation in this bridge across species)
what does penicillin do?
blocks the crosslinking in the peptidoglycan cell wall
what does lysozyme do? where is it found?
in tears and other body fluids
splits the glycosidic bond between NAG and muramic acid
can digest wall of some bacteria
how do the cell walls of gram positive and gram negative bacteria differ?
gram positive have a thick layer of peptidoglycan and mostly different carbohydrate polymers, no phospholipid outer membrane
what type of molecule is ribitol?
sugar alcohol
what is the antibody response of hosts directed toward in bacterial infections?
toward polymers in peptidoglycan rather than peptidoglycan itself
what are the defining characteristics of gram-negative bacterial cell walls?
peptidoglycan layer is thinner than in gram-pos
have an outer membrane - outer surface of this contains lipoposaccharide (LPS)
gram positive have no phospholipid outer membrane!
which type of bacteria is more susceptible to antibiotics and disinfectants? why?
gram positive
gram negative bacteria have outer membrane, which protects them from antibiotics and detergents
describe the layers of the gram-negative bacterial envelope.
inner layer = plasma membrane made of phospholipid, containing integral proteins
periplasmic space containing peptidoglycan, some binding proteins and some digestive or hydrolytic enzymes (gram + don’t have periplasmic space)
outer membrane of phospholipid containing porins
lipopolysaccharide on outer side of outer membrane
describe the layers of gram-positive bacterial envelope. (how is it different from gram-neg)
inner cytoplasmic membrane
thick peptidoglycan layer
wall-associated proteins, teichoic acid, and lipoteicchoic acid on outer layer of peptidoglycan layer
no periplasmic space!
much thicker peptidoglycan layer than gram -
what is the purpose of the gram-negative outer membrane?
blocks entry of large molecules into periplasmic space
also barrier to antimicrobial agents and detergents
what part of gram-negative bacteria reacts with antibodies?
outer membrane
what forms the outer membrane barrier in gram-neg bacteria?
porins = matrix proteins that only let smaller molecules through
how does transport across the outer and inner membrane in gram-neg bacteria vary?
porins in outer membrane allows for non-specific entry of small molecules
there’s active transport in the inner membrane so it’s specific
what types of mutations could affect antibiotics ability to affect a gram-neg bacteria?
mutation in porins - since antibiotics can gain access to the bacterium through porins
what is endotoxin? what is it composed of?
another name for the lipopolysaccharide on the outer layer of the outer membrane in gram-neg bacteria
made of polysaccharide and lipid A
what is lipid A composed of? what is it a component of? where is it found
composed of glucosamine linked to FA and pyrophosphate
component of endotoxin in gram neg cells
inbedded within the lipid bilayer of the outer membrane
what determines the immunologic specificity of gram-neg cells?
the sugars in the outer layer of the polysaccharide in the endotoxin - called O antigens since this outer layer of the polysaccharid is called the O layer
what is the medical importance of the periplasmic space (in terms of the effectiveness of antibiotics)?
can be degrative enzymes in the space that could degrade the antibiotics and prevent them from being effective
where are degrative enzymes found in gram negative versus in gram positive bacteria?
in gram negative, in the periplasmic space
in gram positive, these enzymes are either secreted or are attached to the cell wall
what is the procedure for gram staining?
1: stain cell with crystal violet, a basic dye
2: treat with iodine - forms water insoluble complex with crystal violet inside of the bacterium
3: decolorize with a brief treatment with 70% ethanol - gram negatives will decolorize whereas gram positives will retain dye-iodine complex and appear blue
4: counterstain the decolorized (gram negative cells) with a red stains
so: gram positive is blue, gram negative is red
what is the most likely mechanism of the gram stain?
most likely a permeability difference in cell walls
gram positive cell walls become mostly impermeable to low molecular weight compounds when the organisms are in 70% alcohol - dehydration by alcohol likely traps dye-iodine complex
gram neg have only thin layer of mucopeptide polymer and thick outer membrane whereas gram pos have mostly mucopeptides and polysaccharides - higher mucopeptide content likely retains dye
what happens if the cell wall is removed from a gram-positive cell (in terms of gram staining)?
will react as a gram negative (must always use fresh cultures for gram stains because integrity of cell wall can decline in culture and so old cultures of gram positive can stain as gram neg)
what is the capsule and what is it’s importance to bacteria?
non-essential secretion on the cell surface
usually polysaccharide in composition - different from cell wall
- role in disease production
- antibodies can be directed toward it - vaccines often comprised of capsule or capsule components
- many bacteria don’t have
- can be composed of loose slime or well-formed capsule - can detect capsular antigens in urine often
- has role in resisting phagocytosis
how big are flagella?
10-20 nm thick
8-12 um long (much longer than the cell)
describe the chemical composition of flagella
composed of proteins called flagellins
long helical filament of repeating flagellin subunits with hollow tube down middle
how would you see flagella?
using EM or stains - too thin to see with light microscope
what are the two different types of flagella (in terms of distribution on cell)?
said it’s not necessary to remember the names
many flagella over whole surface = peritrichous
originate from only one end (or from both ends, but only on the ends) = polar
which bacteria contain flagella?
all motile bacteria
how do flagella propel a cell?
like a propeller
spin around axis
what are pili? how do they compare to flagella?
filamentous surface appendages
shorter than flagella
note: can be use interchangeably with fimbrae except in terms of DNA transfer
what is the function of pili?
adherence to other cells, either bacterial or animal - important for bacterial colonization
also sex pili (F pili) that are necessary for reproduction
where are F pili found and what are they necessary for?
found only on “male” donor strains of bacteria
necessary for bacterial conjugation => transfer of DNA from one cell to another
what is the function of sex pili?
bacterial attachement during conjugation
what is the function of type IV pili?
can extend and retract - push or pull bacteria across surface = twitching motility - may allow for the formation of small clusters (microcolonies) on host cells
what is the molecular structure of pili?
hollow tubes assembled by polymerization
what is the function of fimbriae?
allow attachment of bacterial cell to host surfaces
important for bacterial survival within host
how do pili attach to host cells?
recognize and bind to specific sugar residues on polysaccharides on surface of mammalian cells
can also bind to certain receptors on mammalian cells - prevents them from being washed away
besides pili and fimbrae, how do bacteria adhere to host cells?
in gram positive, carbohydrate polymers located on surface of cell wall = glycocalyx/slime layer
proteins on outer surfaces can also serve as adhesins
what induces spore their formation?
only in a few species - nutrient deprivation and other signals trigger formation of spore from bacteria
where is the spore produced? what is unique about it versus other components made by the bacterium?
produced within bacterial cell (endospore)
certain chemicals only in spores (such as dipicolinic acid)
what are spores resistant to?
drying, heat, and chemicals, most can survive boiling up to 121 degrees C
what are spores coated with?
a keratin-like proteinaceous outer coat
how would you stain for spores?
you wouldn’t - they’re resistant to staining - remain colorless in gram stain
what is spore germination and what triggers?
when spore converts back into normal bacterial cell
occurs in response to specific trigger like presence of a specific nutrient
what are the processes behind germination?
loss of heat resistance, swelling, and accumulation of water
spore coat ruptures and vegetative cell grows out
what is a vegetative cell?
the reproductive, non-spore form of a bacterium
how are spores involved in anthrax (bacillus anthracis)?
likely required for survival in the enviornment - allow them to serve as a bioterror agent cause can be stable for years and germinate in warm, wet nutrient rich enviornements such as the lung
what are some variations you might see in the position and size of spores in rod-shaped bacteria?
characteristic for different species
spore can be centrally located or at the end of the cell
can have larger diamater of cell that produced it
may be round or oval in shape
do bacteria respond to chemotaxis?
yes - various sugars and AA present in the growth medium serve as attractants and other substance such as acids or phenols can repell
how do bacteria sense stimuli for chemotaxis?
have sensory chemoreceptors in the rmembrane that control a phospho-cascade - controls direction of flagellar rotation
what controls net movement of flagellum?
direction flagellum is rotating
counter-clockwise results in straight line
reversed - organism tumbles in place
if moving in direction of attractant, straight line occurs more often than tumbles
tumbling more often if moving away from something
what do Koch’s postulates not apply to?
obligate intracellular pathogens
organisms we have not yet learned how to culture
where do all pathogenic bacteria acquire their energy?
require organic compounds as energy source
some of the non-pathogens are photosynthetic
how is arrangement of cells determined by the way cells divide?
successive divisions along the same axis result in chain eg streptococci
successive divisions in any direction => irregular clusters eg. staphylococci
what occurs in the bacterial nucleoid?
DNA is transcribed into RNA in the chromosome - simultaneously translated - no splicing occurs
in which type of bacteria would you find teichoic acid?
gram positive
what is the O-antigen?
on gram-neg cell wall - lipopolysaccharide (LPS) - antigenic determinant
what is an endospore?
spore that is produced within the bacterial cell
