(B) Lecture 11: Intro to Bacteriology Flashcards
Prokaryotes
- smallest, simplest and most abundant cells on Earth
- include Bacteria + Archaea
- NO nucleus + NO complex organelles
Bacteria growth
- reproduce by binary fission (grow fast)
4 phases of growth
- lag (get nutrients)
- logarithmic growth (FAST - doubling_
- stationary (run out of nutrients- waste)
- death
Generation/doubling time in logarithmic phase
Bacteria shape classification
- Coccus (sphere)
- Rod (bacillus)
- Spirillum
Bacterial classification by O2 use
Obligate aerobe
Obligate anaerobe
Facultative anaerobe
Aeroteolerant anaerobe
Microaerophile
Obligate aerobe
require oxygen for growth
Obligate anaerobe
oxygen is toxic for growth
Facultative aerobe
can use oxygen is present but can also grow without oxygen
Aerotolerant anaerobe
doesn’t use oxygen but oxygen is not toxic
Microaerophile
grows best with LOW levels of oxygen
Naming of bacteria
Genus comes first capitalized then species is not capitalized
Basic bacterial cellular structure
- nucleoid: houses genetic material (not nucleus b/c not membrane-bound)
- ribosomes: make protein
- plasmid
- cytoplasmic membrane
- cytoplasm
- cell wall
- cell envelope
Gram stain
2 types of bacteria
- Warm slide w/ sample up on a flame
- Add crystal violet
- Add iodine - helps purple stick in cell wall
- Wash slide w/ alcohol
- gram + = thick cell wall = keeps purple
- gram - = thin cell wall = purple washes - add safranin
- stains gram -
Acid fast (myobacteria) don’t stain
- Gram-positive = PURPLE
- Gram-negative = PINK
Purple and pink in gram stain
PURPLE = Gram-positive
PINK = Gram-negative
Gram + vs Gram -
Gram-positive = cell wall/peptidoglycan is very THICK
- purple dye gets trapped in cell wall
Gram-negative = THIN cell wall (2 separate membranes)
- outer layer made of LPS
Bacterial cell walls
- called peptidoglycan
- RIGID structure
- prevents osmotic lysis
- glycan backbone (G + M alternate)
- peptide cross-linkage btwn glycan cells
humans don’t have these cell walls, so they are good to target w/ antibiotics
Lipopolysaccharide (LPS)
ONLY in gram-negative bacteria
Endotoxin
- O-specific polysaccharide (aka O-antigen): antigenic + highly variable
- core polysaccharide
Lipid A is main part : disaccharide + fatty acid groups
- recognized by INNATE immune system
- recognized by Toll-like receptors
- induces inflammation
- can lead to septic shock due to cytokine storm
Nucleoid
- NOT the nucleus (bacteria do not have a nucleus)
- NO surrounding membrane
- single, circular chromosome (most)
- haploid genomes (one set of chromosome)
Plasmids
- extra-chromosomal genetic elements
- usually not required for bacterial growth
- often encode for FITNESS factors (ex. antibiotic resistance, selective adv.)
- can be transferred from bacteria to bacteria
Human microbiota
- internal organs are usually sterile
- surface tissues have lots of microbes - open to environment (ex. large intestine has most of microbes in body)
Where are most microbes in the body found?
In the large intestine
Host-microbe relationships
- Commensalism
- Mutualism
- Parasitism
Commensalism
one benefits without helping or hurting the other
Mutualism
BOTH benefit (host and microbe)
Parasitism
One benefits (usually microbe) at expense of the other (usually host)
What makes bacterial pathogen successful?
- colonization
- invasion/toxicity
- immune evasion
- transmission
w/o toxicity + immune evasion, a lot of bacteria won’t cause disease
they produce virulence factors - contribute to disease
Virulence factors
Surface
- LPS (endotoxin)
- flagella
- pili and adhesins
- capsules
- secretion systems
Secreted
- EXOTOXINS (bacterial infection is localized but systemic response)
Flagella
- structures that allow some bacteria to be MOTILE (CHEMOTAXIS)
CLOCKWISE = random direction/tumble
COUNTERCLOCKWISE = FORWARD (produces run and goes toward attractant)
Pili
a.k.a. fimbrae
Primarily involved in ATTACHMENT to:
- surfaces
- host tissue
- other bacteria
Capsules
- usually made of (exo)polysaccharides
- attachment to host tissues
- PROTECTION FROM HOST IMMUNE SYSTEM
- can sometimes be used in vaccines
- formation of biofilms (bind to cell surface of bacteria + make colonies to form exopolysaccharides = forms biofilms)
Biofilms
Stages
- attachment
- microcolony development
- biofilm development
- maturation
Endospores
ONLY in gram-POSITIVE
- highly differentiated cells formed within parent cell
- HIGHLY RESISTANT TO HEAT, HARSH CHEMICALS + RADIATION
- a “dormant” stage of life cycle
- most common in soil, bacillus and clostridium
Exotoxins
- SECRETED from bacteria
Includes
1. hemolysins (lyse red blood cells)
2. toxins that function inside host cells
3. extracellular enzymes (destroy proteins, DNAses, lipids, non-specific virulence factors)
4. Superantigens (activate T cells = cause toxic shock)
Some exotoxins (inactivated) can be used as vaccines
Intracellular pathogen
taken up and survive within phagocytic cells
- some force their own uptake into epithelial cells
- allows BACTERIA TO HIDE from different component of immune system
