Bacterial Morphology And Growth Flashcards
What is happening during the death/decline phase?
There are insufficient resources for cell growth, so the bacteria begin dying exponentially. However, they’re dying at a rate slower than the rate they multiplied during the log phase.
Are endospores part of the reproductive cycle of bacteria?
No**
Can you use OD or biomass to measure the amount of bacteria during the death/decline phase?
No, only CFU
OD and biomass can not differentiate between dead or living cells
What are the 2 clinically important acid-fast organisms you need to know?
Mycobacterium tuberculosis
Nocardia asteroides
What does the keratin coat of endospores do?
Impervious to many chemicals, and the immune system can’t see it
What are the 5 phases of bacterial growth?
Lag phase
Log phase
Late Log phase
Stationary phase
Death/decline phase
What are the 3 antigens we discussed and where are they located?
O antigen: LPS in Gram negative outer membranes
H antigen: filament part of flagellum
K antigen: glycocalyx
What is the first step of identifying an organism?
Isolating it in pure culture.
Usually done by streaking plates with a wire loop
What are the 2 most common bacterial shapes?
Coccus
Bacillus
What is selective media?
Media that inhibits the growth of certain unwanted organisms (ex: has an antibiotic in it)
Only certain organisms will be able to grow
What are the 3 areas of bacterial taxonomy?
Classification- grouping them by certain properties
Nomenclature= naming it
Identification- using a classification scheme to isolate and identify organisms
Is there population growth during the stationary phase of bacterial growth?
NO
Even though they are dividing, they are dying at the same rate (and eating the dead bacteria to make new ones)
What is happening during the stationary phase?
Supplies of energy and nutrients have been exhausted
Resources are renewed by cell death (peptides and nucleic acids released)
Death is equal to division**
NO CHANGE in CFU/mL, OD, or Biomass
What does diplo- mean?
Paired bacteria
How long can endospores last in the environment/
Months to years
What are the features of common pili/fimbriae?
- composed of pilin subunits
- tips have adhesins/lectins that bind to sugars
- arranged in a peritrichous arrangement (all over the surface like hair) that function in adhesion and a “twitching” motility
What is the name of the stain used that gram negative organisms retain?
Safranin
What are the 3 major components of the flagellum?
Filament- spins to propel the bacteria (H Antigen is here)
Hook- attaches filament to basal body
Basal body- anchors into cell wall and membrane
What is a common trigger of endospore formation?
Nutrient depletion.
When conditions get better, the endospore will germinate and produce one cell
True or false:
Many pathogens are capnophilic?
True!
Neisseria
Haemophilus
Helicobacter
What does minimum, optimum, and maximum values mean when it comes to particular environmental parameters that support the growth of a microbe?
Minimum: minimum value (pH, temp, oxygen, etc) that supports growth of microbe
Maximum: maximum value that the organism can tolerate (DOES NOT MEAN MAXIMUM GROWTH!!!)
How does biomass work to measure bacteria?
Your sample is washed, dried, and weighed.
This measures viable AND non-viable cells
What is an example of a fastidious organism that requires enriched media?
Haemophilus/Neisseria
Requires hemin and NAD for growth, so they will not grow on blood agar, only on chocolate agar
(I don’t know if this is important)
If you put an obligate anaerobe into liquid in a test tube, where will it grow?
At the bottom
What are the 3 classifications for bacteria types regarding their pH preferences?
Acidophiles
Neutrophiles (most pathogens)
Alkaliphiles
What two stains are used to stain acid fast organisms?
Primary stain: carbol fuschin
Counterstain: methylene blue
What is a function of many inclusions/inclusion bodies?
Storage depots (collections of nutrients etc so it can divide at a moment’s notice)
Ex:
Volutin granules- polymers of phosphate
Glycogen granules
PHB granules- chains of B-hydroxybutyric acid
Does differential media select for specific organisms/inhibit growth of certain ones?
No
What are the 2 clinically relevant genera of bacteria that produce endospore?
Bacillus
Clostridium
(Both are gram positive, but the location and size of the spore differs among the different species, so it can help you identify the bacteria)
Where is the periplasmic space and what is in it?
Between the outer membrane and the inner membrane
Contains peptidoglycan, transport proteins, and HYDROLYTIC ENZYMES
What are the 3 components of the outer membrane in gram negative cells?
LPS (most of the outer part of outer membrane)
Trimeric Porins
Lipoprotein
How does the colony forming unit (CFU) test work to measure bacteria?
You dilute a culture, smear it on a plate, then count the number of colonies that grow. Each colony came from 1 cell.
This will measure ONLY viable cells
What are the 3 ways we can measure bacterial growth?
Optical Density
Colony Forming Units- only one that measures viable cells
Biomass
Where is the peptidoglycan in gram negative bacteria?
In the periplasmic space
What are plasmids?
Other bits of dna outside the main chromosome that contain ancillary information (not essential for cell survival)
Ex: antibiotics, antibiotic resistance, heavy metal resistance, toxins, etc. things that increase its virulence
If you have a mixed infection, how do you isolate a single organism?
You first need to streak the sample onto a plate by doing 3 streak series, diluting the number of cells each time. (See slide 66)
Once those colonies grow, they will be far enough apart to see the different types. Pick a colony of the organism you want, and streak it on a new plate to make a pure culture.
What are halophiles?
Bacterita that require high salt
What does Lipid A do?
It is a heat-stable endotoxin embedded in the outer membrane of gram negative cells.
When the cell is lysed, it gets released and makes your immune system go berserk. It is a B cell nitrogen, and induces cytokines and inflammatory mediators.
~~responsible for bacterial sepsis!
In what 2 ways do LTAs and WTAs increase the virulence of gram positive organisms?
- Function as adhesins- they are sticky and adhere to host cells to begin invasion
- Initiate endotoxin-like activities when released (along with peptidoglycan)
What does the core polysaccharide do?
It connects the O antigen to Lipid A
What does the O antigen do?
Its a sticky sugar that attaches to host cells (inhibits phagocytosis)
It is also highly variable and immunogenic, used to identify bacterial strains
In peptidoglycan, you have chains of NAM and NAG that are cross linked by tetrapeptides. Which disaccharide do the tetrapeptides hang off of?
NAM
What kind of proteins are embedded in the mycolic acid layer of acid-fast cell walls?
Tetrameric porins
Gram negative had TRImeric
What is complex/undefined media?
Media where we don’t know the EXACT composition.
Ex: yeast extract media or potato extract agar
What happens when its too hot for bacteria?
Denaturing structural proteins
Denaturing enzymes
What two structures are in the peptidoglycan layer of gram positive cells that increase their virulence?
Wall teichoic acids WTA (anchored to peptidoglycan)
Lipoteichoic acids LTA (anchored to cell membrane)
Which is more expensive:
Defined media or complex media
Defined
What does sarcina mean?
A packet of 8 cells
What is the difference between obligate and facultative?
Obligate: no alternative
Facultative: has alternatives and can survive in different conditions
What are osmophiles?
Bacteria that require high osmolarity/sugar
What is a glycocalyx?
The “sugar coating” outside the cell wall. May be a capsule or a slime layer.
It is a virulence factor that helps the bacteria: Avoid dessication Acts as a barrier from toxic molecules Inhibits phagocytosis Promotes adherence to cells/surfaces Induces abscess formation Decreases complement-mediated lysis
What is happening during the log phase of bacterial growth?
Exponential growth and rapid cell division
Bacteria are producing metabolites and virulence factors
What are microaerophiles?
Bacteria that require oxygen, but at lower levels than obligate/strict aerobes
How does optical density work to measure bacterial growth?
You measure how much light the cloudy tube of bacteria absorbs and you can find out how many are in there.
Measures viable AND non-viable cells (dead cells still absorb light)
Which has a narrower range of growth: defined media or complex media
Defined
Obviously, acid-fast bacteria do not stain with Gram stain. Does that mean that they don’t have any peptidoglycan?
No, they do have peptidoglycan, but it has a waxy coating that repels the stain
What is happening during the late log phase?
They are starting to run out of nutrients and space to grow, so they start producing secondary metabolites like antibiotics and pigments to kill off competition
What does strepto- mean?
Bacteria are in a chain
What is happening during the lag phase of bacterial growth?
The bacteria are increasing their biomass, but not dividing.
They’re getting ready to divide
What kind of ribosomes do bacteria have?
70S (30S + 50S subunits)
Different than human ribosomes
Transcription and translation are coupled
What are the 3 enzymes that bacteria can make to counteract reactive oxygen species?
Superoxide dismutase
Catalase
Peroxidase
What does the length of the lag phase depend on?
Availability of nutrients
Condition of inoculum
What is differential media?
Media that differentiates between organisms.
It has components that will result in a visible change if certain bacteria grow on it. (Ex: color change)
What does lipoprotein do?
Anchors the outer membrane to the peptidoglycan layer (gram negative cells)
What are the 2 types of pili?
Common pili/fimbriae
Sex pili
If you put a facultative anaerobe into liquid in a test tube, where will it grow?
All throughout the liquid (Top, bottom, middle )
What is the only kind of bacteria that does NOT have enzymes for reactive oxygen species?
Obligate/strict anaerobes
Oxygen will kill them
What do pili do?
They are little hairs with adhesins at the tips that help the bacteria adhere to each other or to host cells
How do bacteria replicate?
Binary fission
1 bacteria replicates its DNA and gets bigger, then it separates into 2 genetically identical bacteria
Will antibiotics that inhibit cell wall synthesis work on cells that are not actively growing/
No
What are capnophiles?
Bacteria that require high CO2 levels (3-5%)
What does staphylo- mean?
Grapelike cluster
What is enriched media and what is the benefit of it?
It is complex media that has growth factors added to it.
Used for growing fastidious organisms (finicky)
Do facultative aerobes/anaerobes require oxygen?
No, but they will use it if it’s available
They also have enzymes for reactive oxygen species
How do you grow capnophiles in the lab?
Candle jars, CO2 packets, automated systems
What does pleomorphic mean?
No defined shape
What is the difference between an obligate anaerobe and an aerotolerant anaerobe?
The aerotolerant anaerobe has enzymes to detoxify reactive oxygen species
The obligate/strict anaerobe does not have these enzymes, so oxygen is toxic to them.
What kind of media is required to grow fastidious organisms?
Enriched media
You won’t find them if you try to use anything else
Where is the H antigen located?
In the filament portion of the flagellum
Which two proteins are found in the outer membrane of gram negative cells? (Not in the LPS part)
Trimeric protein channels/porins
Lipoproteins (most abundant protein in gram negative cells)
What kinds of bacteria are resistant to dessication?
Spore forming (bacillus and clostridium)
Cell wall modification (mycobacterium and their mycolic acids)
Most pathogenic bacteria are _________
Mesophiles
Is the cell wall internal or external to the cell membrane?
External
What part of the gram negative bacteria is responsible for bacterial sepsis?
Lipid A
(It directly activates the alternative complement pathway, and then casues the release of cytokines and other inflammatory mediators)
What kind of bacteria can grow on MacConkey agar?
Gram negative ONLY
Would be good for enteric infections, since most of those are Gram -
What are mesophiles?
Bacteria that can live in temperatures from 12-42°C, but LOVE living from 30-37°C
(Body temperature)
Does the bacterial cell membrane contain sterols?
No
Some exceptions
Where is the K antigen?
In the glycocalyx
What does tetrads mean?
Packets of 4 bacterial cells
What are 2 ways that organisms can interfere with peptidoglycan to try to kill bacteria? (Not human made antibiotics)
- Secreting antimicrobial compounds
2. Secretion of lysozyme
What are inclusion bodies?
Collective term for granules, vesicles and vacuoles within the cytoplasm
How does lysozyme work to interfere with peptidoglycan?
Degrades the glycan backbone to weaken the integrity of the cell wall EVEN IN bacteria that are NOT actively growing
What are endospores?
Resting stage of bacteria that contains:
1 chromosome
Small amounts of proteins and ribosomes
Peptidoglycan
High concentration of calcium bound to dipicolinic acid*
Keratin spore coat** (not noticeable to immune system)
Do bacteria have a defined nucleus?
No they have a nuclear region/nucleotide with a single circular chromosome
If you put an obligate aerobe into liquid in a test tube, where will it grow?
At the surface
What is the name of the stain used that gram-positive organisms retain?
Crystal violet
What is defined media?
It has known quantities of each component (carbon, nitrogen, etc)
What is the difference in glycocalyx types: capsule vs slime layer?
Capsule: rigid shell that closely surrounds the cell
Slime layer: loose, non-uniform, diffuse
How does the mycolic acid layer of acid fast cells help them?
It gives the organism a waxy coat that functions to resist dessication, antibiotics, and phagocytosis.
(It “hides” the bacteria from the immune system and it can take as long as it wants to grow)
Where are trimeric protein channels (porins) located and what do they do?
They are in the outer membrane of gram neg cells (not the LPS part)
They are nonspecific channels that let water and small molecules across the membrane
What does a sex pili do?
Adheres two cells together to allow for conjugation aka the exchange of DNA
What kind of media is MacConkey Agar?
Differential AND Selective
It has bile salts and crystal violet that inhibit Gram positive bacteria from growing
It also has “neutral red,” a pH indicator that will change color if the bacteria that grows can ferment LACTOSE or not
What happens to bacteria when it’s too cold for them
Loss of enzyme activity
Decreased membrane fluidity
What are the 3 parts of the LPS in order from external to internal?
O antigen
Core polysaccharide
Lipid A
Where is the periplasmic space located?
In between the inner and outer membranes of gram negative bacteria
What does the calcium dipicolinate in endospores do?
Heat resistance
