Wk 1 Bacteriology 1 & 2 Flashcards
Phylogenetic Tree of Life
Human-associated microbiota
What is colonization resistance?
microbiota inhibits colonization by newcomers
-high diversity and density -> high CR
How are bacteria named?
each organism gets 2 names:
1. Genus is the first name, always capitalized
2. species is second, not capitalized
-both either underlined or italicized
-“species” is singular and plural
Taxonomy of bacteria
Domain
Phylum
Class
Order
Family
Genus
Species
Strain
What do eukaryotic and bacterial cells have in common?
- cell membrane
- cytoplasm
- ribosomes
- DNA
What do bacteria cells have that eukaryotic cells don’t?
- simple structure
- no prominent nucleus
- circular DNA
- single, haploid chromosome
- small size
- cell wall w/ peptidoglycan
- 70S ribosomes
- no organelles
- cells divide by binary fission
What do eukaryotic cells have that bacteria cells don’t?
- complex structures
- prominent nucleus
- linear DNA
- paired diploid chromosome
- large size
- cell wall (chitin, cellulose)
- 80S ribosomes
- membrane-bound organelles
- cell division by mitosis
Compare eukaryotic and bacterial cells
What are 3 ways to classify bacteria?
- morphology
- cell wall structure - Gram staining
- Oxygen requirements and metabolism
What is the role of peptidoglycan?
Main structural component of the bacterial cell wall
What is -emia?
In the blood
Mycoplasma
Bacteria with NO cell wall
acid-fast bacteria
-resist decolorization
*Mycobacteria and Nocardia *
Functions of bacterial cell wall
-multilayered structure
-provides structural integrity
-allows nutrients/waste transport
-rigid, determines shape
-respiratory chains
-adhesions
-basis for serotyping pathogens: Antigens: O (LPS), K (capsule), H (flagellin)
What are the parts of a LPS?
=lipopolysaccharide (integral for Gram-negative bacteria)
1. Lipid A - region (endotoxin), conserved, responsible for fever and shock
2. Core oligosaccharide of 5 sugars
3. O antigen - immunogenic and accounts for virulence of Gram-negative bacteria
Mycobacteria
Does not stain or stains weakly Gram-positive
-cell wall has high lipid content - mycolic acids and lipoarabinomannan (LAM), a glycolipid
Bacterial Metabolism
Energy Production in Bacteria
What are obligate aerobes?
require oxygen
What are facultative anaerobes?
can grow w/ or w/o oxygen
-some can carry out anaerobic respiration by using alternate electron acceptors
Microaerophilic bacteria
Can survive in very low levels of O2
Obligate Anaerobes
Are poisoned by oxygen
How are aerobic and anaerobic bacteria identified?
Grow them in test tubes of thioglycolate broth
How are aerobic or facultative bacteria determined?
Are catalase positive
What bacterial cell structures contribute to virulence?
- protein secretion systems
- toxins
- flagella
- adhesins: pili and fimbriae
- capsules
- spores
What are protein secretion systems?
Proteins with toxins synthesized by bacteria, secreted by specialized structures w/ syringe-like injectors (AKA injectosome or a needle-like protein)
What are exotoxins?
usually secreted by bacteria, sometimes by lysis of the bacterial cell
-enter eukaryotic cells through receptor-mediated endocytosis
-virulent strains produce toxin = major determinant of virulence
-many are pore-forming molecules w/ A-B components (B=binding, triggers endocytosis and A=active, enzyme activity)
Endotoxins
=cell-associated substances that are structural components of the outer membrane (LPS) of Gram-negative bacteria
-released from growing bacterial cells
-released from cells lysed from effective host defense (eg lysozyme)
-released from activities of certain antibiotics (eg penicillin)
5 types of exotoxins
- enterotoxins - act in GI tract -> diarrhea
- Neurotoxin -> paralysis
- pyrogenic exotoxins ->cytokine release -> rash, fever, toxic shock syndrome (eg Superantigens)
- Tissue invasive exotoxins - allow bacteria to penetrate or circumvent cell and tissue barriers (eg DNAses, pore-forming toxins)
- others: there are many. Can affect very specific host factors, cell signaling mechanism, protein synthesis
Superantigens
-Bind to MHC class II of antigen presenting cells and activate T cell receptor
-Massive and uncontrolled release of cytokines (TNF, IL-1, IL-6, IFN-γ)
-Nitric oxide release →capillary leak →toxic shock
2 examples of superantigens
Toxic shock syndrome toxin (TSST-1)
* Staphylococcus aureus
* Excessive cytokine production leads to fever, rash, toxic shock and vascular rash
* Scalded skin syndrome and food poisoning
Streptococcal pyrogenic exotoxin A
* Streptococcus pyogenes
* Toxic shock-like syndrome, fever, rash, shock, scarlet fever
Characteristics of endotoxins
- Lipopolysaccharide in the cell walls of Gram- negative organisms
- Heat-stable
- Released into the body
- Via cell lysis or detachment
- Not actively secreted (unlike exotoxins)
- Bacterial lysis due to antibiotic treatment
- Hyper-inflammation can lead to Sepsis and Septic shock, Organ failure, Acute respiratory syndrome
Exotoxins vs Endotoxins
What are flagella?
facilitate motility and adhesion
-imp virulence factors (H antigen)
-ex Helicobacter pylori, E. coli, spirochetes
What are bacterial adhesins?
Bacterial adhesin proteins are often associated with hair-like fibers called pili or fimbriae
-Can act as receptors for phage, promote conjugation (genetic exchange), and mediate biofilm formation
- Anti-adhesins being developed as anti- bacterial therapeutics
What is biofilm?
A colony of same species of bacteria w/ protection from external environment
-promote bacterial colonization and persistence
Bacterial capsules
- Layers of polysaccharide (or polypeptide) associated with the bacterial surface, made of K antigen
-protection
-antibodies against specific capsule K antigen
-main component of some vaccines
What are 5 encapsulated bacteria that are opsonized and then cleared by the spleen?
- Streptococcus pneumoniae * Hemophilus influenzae
- Neisseria meningitidis
- Escherichia coli
- Salmonella typhi
- Klebsiella pneumoniae
What are spores?
- Some Gram-positive bacteria can form spores
- Spores form when there is shortage of nutrients
- Spores lack metabolic activity
- Core contains dipicolonic acid (heat resistance)
-pretty inert and resistant to antimicrobials
ex C. difficile
-most antibiotics will not kill spores (neither will hand sanitizers)
Medically important spore-forming bacteria
Bacterial cell replication
Binary fission:
1. DNA replication
2. chromosome segregation
3. cytokinesis
What are the phases of binary fission?
- lag phase- metabolic activity, no division
- log phase - rapid cell division
- stationary phase - nutrients depleted, growth slows, spores form
- death phase - waste products accumulate ->death
How do transcription and translation occur in bacterial cells?
They are coupled and occur at the same time
What are 4 methods of genetic exchange for bacteria?
- transformation
- conjugation
- transduction
- transposition
Horizontal Gene Transfer (HGT) allows for the rapid exchange and spread of virulence determinants and antibiotic resistance genes.
What changes in DNA base sequences -> altered phenotypes?
- base substitution
- frameshift
- transposons (insertion sequence)
What do altered bacterial genetics allow for?
- antibiotic resistance
- transfer of antibiotic resistance genes
- evade host immune system
What is horizontal gene transfer (HGT)
- transformation
- transduction
- conjugation
What is bacterial transformation?
DNA is taken up directly by cells.
* Bacteria able to take up DNA are said to be
“competent”.
What is transduction?
=transfer of DNA mediated by bacteriophages
-viruses that replicate w/in bacteria
-found wherever bacteria is found
What is the phage life cycle?
Lytic and lysogenic phases
-prophage can carry important fitness and virulence determinants
What is conjugation?
Add description
-uses sex pili
What are 4 plasmid types?
Fertility F-plasmids: contain tra genes for transfer. They are capable of conjugation and result in the expression of sex pili.
Col plasmids: contain genes that code for bacteriocins (proteins that can kill other bacteria). Some are also toxic to host cells (genotoxins)
Virulence plasmids: encode virulence factors, can convert a bacterium into a pathogen. (e.g. pathogenic Salmonella strains)
Resistance (R) plasmids: contain genes that provide resistance against antibiotics or poisons. Historically known as R-factors, before the nature of plasmids was understood.
What is transposition?
Transposable elements allow for gene transfer, transposon movement, can carry virulence and antibiotic-resistance genes
What do capsules protect from?
phagocytosis
