Bacteria Flashcards
Examples of prokaryotes vs eukaryotes
Prokaryotes = archaea & bacteria Eukaryotes = humans, plants, parasites, fungi
Features of Prokaryotes
- Single-celled organisms
- No nucleus or membrane-bound organelles
Difference between bacteria and archaea? (the two prokaryotes)
Archaea are like bacteria but have different:
- RNA molecules
- Different constituents in their cell wall and slightly more complex biochemical pathways
- ARCHAEA ARE NOT KNOWN TO CAUSE HUMAN DISEASE (not pathogens)
Where are bacteria found?
On almost all surfaces of Earth! (soil, acidic niches, waters, hot springs)
-Outside and inside cavities of our bodies
Microbiome (definition)
Commensal (definition)
Microbiome = body’s collection of microorganisms
Commensal (good) bacteria = 1-3% of the body’s mass
T/F bacteria are composed of one or more cells – they are singled celled organisms
True
Asexual or sexual reproduction?
Reproduce primarily via asexual means, but can undergo forms of sexual reproduction
Explain the Morphology of Bacteria:
Cocci
Bacillus
Spirals
Staphylo
Strepto
Diplo
Cocci = round
Bacillus = rods
Spirals
Staphylo - clustered
Strepto - straight chains
Diplo - clusters of two bacterial cells
Make up of bacteria: Cell Wall - Y/N? Plasma Membrane (with components)? Ribosome? Membrane-bound organelles?
Cell wall = yes
Plasma membrane = yes, lipid bilayer, but no carbohydrates or sterols
Ribosome = yes, smaller than eukaryotic, = 50S + 30S = 70S ribosome
Membrane-bound organelles = NO!
Bacterial Cell Walls
- Function
- What targets this?
- Contains what?
Function = maintains shape & provides physical protection
Targets this = antibiotics target bacterial cell walls
Made of = polymer of sugars & amino acids called “PEPTIDOGLYCAN”
What is peptidoglycan?
A polymer of sugars and amino acids in bacterial cell walls
Gram-Positive vs Gram-Negative Bacteria
Gram-Positive Bacteria:
- Plasma membrane = single plasma membrane
- Cell wall = Thick peptidoglycan layer
- Containing teichoic acids
- PG integrity owing to cross-linked NAGs and NAMs
Gram-Negative Bacteria:
- Plamsa membrane = double plasma membrane!!
- Inner Plasma Membrane
- Cell wall = thin cell wall with less peptidoglycan
- Outer Plasma Membrane = outer leaflet contains LSP (endotoxin)!!!!
T/F - bacteria produce toxins (poisonous substances produced by living organisms)
TRUE
Exotoxin vs Endotoxin
EXOtoxin - secreted by bacteria and released outside the cell
ENDOtoxin - bacterial toxins located within or on the cell
NOTE: “endotoxin” generally refers to LPS (the major component of the outer membrane of gram-negative bacteria)
Lipopolysaccharide (LPS)
Decorates the outer leaflet of the outer membrane of gram-negative bacteria
-Structural integrity and protection from chemical attack
What does “Gram” refer to?
The staining technique
Gram positive vs gram negative stain colour
Gram positive = purple
Gram negative = pink
4 steps of gram staining
- Application of crystal violet (purple dye)… binds thick PG layer
- Application of iodine (mordant)… I fixes the stain
- Alcohol wash… Alcohol removes weakly bound CV
- Application of safranin (counterstain)… safranin (pink/red) is added to decolourized bacteria
Bacterial Structures - Glycocalyx
All bacteria are covered by a network of polysaccharides that surround the cell membrane called “glycocalyx”
- Capsule
- Slime (“biofilm)
- Important for limiting desiccation, protection from toxins or infection, and aiding with adherence to cells & other bacteria
Note: capsules can impair immune processes! Phagocytosis!
Bacterial Structures - Biofilms
Biofilm = an aggregation of microorganisms in which they stick to each other an also to a surface
–Adhere using slime (glycocalyx)
Fimbrae vs Pili vs Flagella
Fimbriae = bristle-like appendages often present in multiple numbers, used for adherence to host cells
Pili = filamentous structures present in singly or in pairs. Used for bacterial conjugation, whereby genetic material is exchanged b/w 2 bacteria (sex pilus)
Flagella = tail-like projections, allow bacteria to move around (motility), rotary movement (diff. from eukaryotic flagella)
What are Secretion Systems & Efflux Pumps used for?
Secretion Systems - are specialized structures for injecting exotoxins into target cells
- -Found in some gram-negative bacteria
- Needle-like protein
Efflux Pumps - some bacteria have efflux pumps that shoot out antibiotics (inherent antibiotic resistance)
Bacterial Genetics - nuclei? Location of DNA? Chromosomes?
Bacteria do NOT have nuclei inside their cells
They contain a tangled region of circular double-stranded DNA called the “nucleoid” or “nucleoid region”
-Contains all the essential chromosomes/genes for the bacteria to survive
Plasmids
Plasmids - small extrachromosomal circles of DNA, carried by bacteria
- Encode proteins that are not essential for survival, but provide the bacterial cell w/ an advantage
- Antibiotic-resistance is encoded by plasmid genes
- Plasmids can be passed from one bacterium –> another via pili
Bacteria primarily reproduce through binary fission (asexually)… describe the 5 steps
- Cell replicates DNA
- Cytoplasmic membrane elongates, separating DNA molecules
- Cross wall forms, membranes invaginate
- Cross wall forms completely
- Daughter cells
NO increase in genetic diversity!
Splits and produces two identical daughter cells
Bacterial Growth Stages – describe
- Lag Phase
- Exponential Growth Phase
- Stationary Phase
- Death Phase
- Lag Phase: bacteria are maturing but not yet able to divide
- Exponential Growth Phase: bacteria start dividing, nutrients are abundant, low waste
- Stationary Phase: rate of cell growth = rate of cell death, nutrients depleted, waste
- Death Phase: bacteria die, lack of nutrients, temperature not ideal, waste, other injurious conditions
Bacterial Exponential Growth = y = 2^n
y = colony size n = number of divisions
Bacterial exponential growth depends on the doubling time of the bacterium in question (ranges from 20 mins to 3 hours)
Ex: after 10 rounds of binary fission, y=2^10 = 1024 bacteria
Endospores (Spores)
- Formed by which type of bacteria?
- Dormant form?
- High or low resistance?
Formed by Gram-POSITIVE bacteria
-Stripped down, dormant form to which bacterium can reduce itself when nutrient levels run low!
-Highly-resistant to radiation, detergents, disinfectants, heat, freezing, drying
May remain viable as endospores for decades!
Define:
- Obligate Aerobic Bacteria
- Obligate Anaerobic Bacteria
- Facultative Anaerobic Bacteria
- Microaerophiles
- Aerotolerant Anaerobes
- Obligate Aerobic Bacteria: require O2 for survival
- Obligate Anaerobic Bacteria: do not require oxygen, may be poisoned by atmospheric oxygen levels
- Facultative Anaerobic Bacteria: will use oxygen if it is available, but it is not required for their survival
- Microaerophiles: require oxygen but are poisoned by high concentrations of oxygen
- Aerotolerant Anaerobes: do not require oxygen, as they use fermentation to make ATP
Thioglycollate Broth
- What is it?
- Where do aerobic and anaerobic sit?
It is a thick, semi-soft growth medium
Hard for O2 to penetrate to the bottom of the tube…
Aerobic - near top
Anaerobic - near bottom
Intracellular Vs. Extraceullar Bacteria
Facultative Intracellular Bacteria
Intracellular - dependent on host cells to supply them with energy & other needs
Extracellular - do NOT invade cells, and proliferate in the extracellular enviro (body fluids)
Facultative Intracellular Bacteria - can survive inside or outside of cells
How to detect bacteria?
Collect sample: swabs, feces, CSF, blood urine
- Culture on selective growth media
- Antibiotic sensitivity tests
- Microscopy, stains
- Serology (blood work) –> microbe specific antibodies
- Molecular PCR
What does blood agar test for?
Agar with 10% horse or sheep RBCs
Tests for HEMOLYSIS – ability to lyse RBCs
Beta-hemolysis = complete hemolysis Alpha-hemolysis = partial hemolysis Gamma-hemolysis = NO hemolysis
How do bacteria cause human illness?
- Produce toxins that cause illness
- Damage or kill cells
- Induce local or systemic inflammation
- Dysregulate physiological processes
- Infections continue until hosts develop appropriate immune response or treatment is taken (antibiotics)
What are superbugs?
Give 4 examples
Strains of bacteria that are RESISTANT to certain antibiotic drugs (antimicrobial resistance, AMR)
Why? Occurs naturally, but improper use of antibiotics in humans & animals accelerates process
-Creates selection pressures that allow those with resistance mutations to survive & grow
MRSA (methicillin-resistant Staphylococcus aureus)
VRE (vancomycin-resistant Eneterococcus)
MDR-TB (multi-drug resistant tuberculosis)
CRE - carbapenem-resistant Enterobacteriaceae
Which parts of the body contain commensal bacteria (good bacteria)?
Skin, GI tract, genital & upper respiratory tracts
What is colonization resistance?
Good bacteria that occupy niches that would otherwise be occupied by harmful pathogens
When can good bacteria go bad?
Immunocompromised host
Change to anatomical location
Injury (smoking, trauma, infection)
Antibiotic misuse
Benefits of commensal bacteria
- Produce Vit K and B12
- Metabolism of bile acids, sterols, dietary fiber
- Regulation of vaginal pH
- Development of the immune system
- Nitrogen fixation & decomposition of dead matter
- Food production
- Biological pesticides
- Commercial insulin production
- Digesting hydrocarbons in petroleum (oil spills)
PREbiotics vs PRObiotics
PREbiotics - indigestible dietary fibers that feed the friendly bacteria in your gut
PRObiotics - live microorganisms intended to provide health benefits when consumed, generally by improving or restoring the gut flora
