Bacteriology Flashcards
What are the 3 domains of life
Bacteria, Archaea, Eukaryotes
Prokaryotes
- simplest, smallest and most abundant cells on earth
- bacteria and archaea
- lack nucleus and complex organelles
How do bacteria reproduce
binary fission
T/F: fast growing bacteria are more efficient/evolved than slow growing bacteria?
FALSE
What is the generation time for fast and slow growing bacteria?
Fast: ~ 10 mins
Slow: ~ 24 hrs
What are the 3 classifications of bacteria by shape
Coccus, Rod, Spirillum
Obligate aerobe
requires oxygen for growth (e.g humans)
obligate anaerobe
oxygen is toxic for growth
Facultative anaerobe
can use oxygen if present, but can also grow without oxygen
Aerotolerant anaerobe
does not use oxygen but oxygen is not toxic
Microaerophile
grows best with low levels of oxygen
What is a bacterial strain?
strains are genetically different bacteria - it is like a “name”
- NOT ALL “e.coli” are the same, there are different strains
Gram Stain
Stain used to classify bacteria, created by Hans Christian Gram
What are purple bacteria on the gram stain?
Gram Positive
What are pink bacteria on the gram stain
Gram Negative
What is the process of Gram Staining?
- take swab of bacteria and put on a glass slide
- heat the slide
- flood with crystal violet dye
- add iodine solution which fixes the purple stain into the cell wall
- wash cells with alcohol to get wash dye off (for gram positive bacteria, the dye will remain)
- add counterstain to stain everything that the dye washed off from previously
What are two cases you cannot use the gram stain?
- Mycobacteria (use acid fast)
- bacteria that have no cell wall (mycoplasma)
Gram positive cell envelope
- cell wall is outside the cytoplasmic membrane
- cell wall is very thick and this structure is what maintains the purple
- no outer-membrane
- no periplasm
- have teichoic acids in cell wall
Gram Negative Cell Envelope
- has cell wall but it is very thin
- more complex
- have a second membrane (outer membrane)
- between two membranes there is a “periplasm”
- also have lipopolysaccarides
Another name for Bacterial Cell Walls
- also called peptidoglycan
Describe bacterial cell walls
- rigid structure surrounds bacteria (like a fence)
- prevent osmotic lysis
- gylcan backbone made up of two sugars that are linked together via peptides
- synthesis of cell wall is a major target for cell antibiotics
What are the two sugars that make up the glycan backbone? Of the two sugars, which are cross-linked together via peptides
N-Acetylglucosamine (G) and
N-Acetylmuramic acid (M)
Three components that make up Lipopolysaccharide (Endotoxins) and their functions
O-specific polysaccharide (aka O antigen):
- that sticks out of the surface of bacteria
- Immune system can recognize this and develop antibodies against it
- highly variable
Core polysaccharide:
- Links the O antigen and Lipid A
Lipid A:
- this is the part that actually sticks into and is part of the membrane
- Doesn’t vary much
- Good target for innate immune system to go after and recognize bacteria
- recognized by innate immune system and cause hyper-inflammation, producing cytokine storm and then septic shock
Sometimes bacteria will change this part of the lipopolysaccharide so that it is not recognized by the immune system. Which is it?
O antigen
Nucleoid
- NOT the nucleus
- no surrounding membrane
- Single, circular chromosome (most but not all bacteria)
- Haploid genomes (one set of chromosome)
Plasmids
- Extrachromosomal genetic elements
- Usually not required for bacterial growth (bacteria in the lab can grow without them being present)
- Often encode for ‘fitness’ factors (e.g. antibiotic resistance)
- Can be transferred from bacteria to bacteria
Commensalism
one benefits without helping or hurting the other (e.g. intestinal bacteria)
Mutualism
both the host and microbe are benefited
Parasitism
one benefits (usually the microbe) at the expense of the other (usually the host)
“PARASITE”: usually this term is restricted to eukaryotic pathogens, not bacteria
What makes bacterial pathogen successful?
Cycle of: Colonization, invasion/toxicity (in host), immune evasion (host response), transmission
Virulence factors
molecules produced by the pathogen that contribute to disease
Examples of Virulence Factors
Surface:
- LPS (endotoxin)
- Flagella
- Pili
- Capsules
- Surface Proteins
- Secretion systems
Secreted:
-exotoxins
Flagella
Structures that allow some bacteria to be motile (chemotaxis)
Counter- Clockwise rotation: move forward
Clockwise rotation: tumble around in random direction
- Switch between directions and overtime they will move toward attractant
- If there is no attractant, they randomly tumble/run (no direction)
- Not like they are steering, it’s a random process
Pili (Fimbriae)
Primarily involved in attachment to: surfaces, host tissue, other bacteria
Capsules
- extracellular structures
- made of exo-polysaccharides
- attachment to host tissues
- protection from hose immune system
- can sometimes be used in vaccines
- formation of biofilms
Biofilm
- individual cells bind to surface (e.g. teeth) - ATTACHMENT
- Divide and start to produce capsule (gooey structure) - MICROCOLONY/BIOFILM DEVELOPMENT
- Eventually matures to biofilm structure - MATURATION
- NOT a random pile of goo
- This structure has channels in it to allow nutrients to enter and waste to exit
- Bacteria at bottom of biofilm will have slower growth
Stages of Biofilms
Attachement
Microcolony development
Biofilm development
Maturation
Endospores
- Highly differentiated cells formed within the parent cell
- Highly resistant to heat, harsh chemicals and radiation
- A “dormant” stage of the life cycle
- made only by gram positive
Where are endospores most commonly found?
Most common in:
- Soil
- Bacillus and Clostridium genera are the best studied
Exotoxins
- Highly specialized virulence factors
- Secreted from bacteria (EXO)
- Localized infection but your disease is systemic
(bacteria is only in one place, but the toxin is systemic) - E.g. tetanus
Examples of Exotoxins
- Hemolysins - lyses RBCs
- toxins that function inside the host cells
- Extracellular enzymes – destroy tissue
- Super-antigens – function to turn on adaptive immune systems
Bacteria as intracellular pathogens
- Are 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
