Lecture 1 Flashcards
What is the cell envelope?
External covering outside the cytoplasm
Composed of two basic layers: cell wall and cell membrane
•Maintains cell integrity
What are the properties of a gram-positive bacteria?
thick cell wall composed primarily of peptidoglycan and cell membrane
contains Lipoteichoic acid and Teichoic acid
What are the properties of a gram-negative bacteria?
outer cell membrane, thin peptidoglycan layer, and cell membrane
Outermost layer:
•contains lipopolysaccharides (LPS) and lipoproteins.
•components of it may function as receptors and block immune response
•contains porin proteins to regulate molecules entering and leaving cell through passive diffusion
•Bottom layer composed of phospholipids and lipoproteins
•Periplasmic space surrounds peptidoglycan
What is the purpose of the cell wall?
- Determines cell shape, prevents lysis (bursting) or collapsing due to changing osmotic pressures
- Peptidoglycan is primary component
What is the difference between a gram-negative and positive stain?
Gram-positives - retain crystal violet and stain purple
Gram-negatives - lose crystal violet and stain red from safranin counterstain
What are the movements of Flagella?
Taxis - Bacteria move in response to stimuli
Runs – counterclockwise
Tumbles – clockwise
What are the responses of Flagella in different stimuli?
Chemical stimuli – chemotaxis; positive and negative
Light stimuli – phototaxis
What are the structures of Flagella?
Flagellin protein (filament) is deposited in a helix at the lengthening tip
- Base of filament inserts into the hook
- Basal body anchors filament and hook to cell wall by a rod and a series of either 2 or 4 rings of integral proteins
What are the appendages of Flagella?
Motility – flagella and axial filaments (periplasmic flagella)
Attachment or channels – fimbriae and pili
Glycocalyx – surface coating
What is Fimbriae?
Fine, proteinaceous, hair-like bristles
What is the function of Fimbriae?
Function in adhesion to other cells and surfaces
What is a capsule?
- Composed of organized repeating units of organic chemicals; usually consists of polysaccharides
- Firmly attached to cell surface
What is the function of the capsule?
- Protects cells from drying out
* May prevent bacteria from being recognized and destroyed by host
What is predation?
any interaction between two organisms in which one organism (the predator) consumes all or part of another organism (the prey).
What is competition?
an interaction between two organisms that are using the same limited resource within the same species (intraspecific) or between different species (interspecific).
What is symbiosis?
an intimate relationship between different species in which at least one species depends upon the relationship to survive.
-mutualism, commensalism, and parasitism
What is mutualism?
Both partners benefit from the relationship (+, +)
e.g., normal flora
What is Flora?
Normal flora is a mixture of microorganisms (bacteria and fungi) that are found at all surfaces of human body
•They constitute a protective host defense mechanism by preventing colonization by pathogens.
At the same time, they can cause disease when individuals become immunocompromised or debilitated, or when they change their usual anatomic location.
What is superinfection?
can result if the normal flora is removed by inappropriate use of antibiotics. Usually, superinfection occurs with resistant microbes
What is commensalism?
One partner benefit from the relationship; the other partner is not affected (+, 0)
What is parasitism?
One partner benefit from the relationship; the other partner is harmed (+, -)
EX: Malaria is a disease caused by a parasitic protozoan of the genus Plasmodium. The protozoan is transferred effectively by mosquitoes (particularly Anopheles).
What are opportunistic pathogens?
only cause disease in immunocompromised hosts, and are often organisms that are typically normal flora.
What are Frank Pathogens?
always associated with disease and can cause disease either in healthy or in immunocompromised individuals
What are Facultative Pathogens?
fall between the two extremes (opportunistic and frank) and the majority of organisms that cause disease fall into this group
What is the difference between pathogenicity and virulence?
Pathogenicity is the potential to cause disease and is applied to groups or species of organisms
Virulence is the degree of pathogenicity within a group or species and is measurable by the LD50 or the LD50
What is the pathogenesis?
the manner by which disease develops, including the chain of molecular events that lead to development of disease by microorganisms
What are the virulence factors?
Capsules Pili IgA protease production Iron capturing ability Production of coagulase Production of toxins Ability to survive inside phagocytic cells
What is LD50?
LD50 is the dose of bacterial micros that can cause 50% of the bacterial population to die, or 50% of disease in the cohort of the species you’re testing in.
What is Quorum sensing?
Bacteria can sense changes in environment
What are the ways in which we can switch virulence genes on and off?
- DNA Sequence modification
o Gene amplification
o Genomic rearrangements: e.g. Hin (DNA invertase) flip-flop control of flagellar phase variation - Transcriptional regulation
o Activators and repressors
o mRNA folding and stability - Translation Regulation
- Post-Translational Regulation
o Protein stability, regulated protein cleavage
o Post-translational modifications: e.g. phosphorylation in two-component sensor-regulator systems
What are the common adherence mechanisms?
- Capsules and slime
- Biofilm formation
What is iron used for?
Diphtheria toxin (DtxR repressor) Shiga-like toxin Pseudomonas aeruginosa exotoxin A
What is genetic recombination?
Genetic recombination - transfer of DNA from one organism (donor) to another recipient (homologous, non- homologous).
What is homologous recombination?
homologous DNA the same nucleotide sequences are exchanged by means of Rec A proteins. This involves breakage and reunion of paired DNA segments.
transformation, transduction, and conjugation
What is transformation?
Genetic recombination in which a DNA fragment from one bacterium enters a competent recipient bacterium and it is exchanged for a piece of the recipient’s DNA.
What is transducation?
Genetic recombination in which a DNA fragment is transferred from one bacterium to another by a bacteriophage
•Bacteriophage (phage) are obligate intracellular parasites that multiply inside bacteria by making use of some or all of the host biosynthetic machinery (i.e., viruses that infect bacteria
What is conjugation?
Rigid tubular structure made of pilin protein
•Found only in gram-negative cells
•Function to join bacterial cells for partial DNA transfer
What are PAI?
PAHOGENTICITY islands (PAIs) are Discrete genetic loci that encode factors which make a microbe more virulent
What are the features of PAI?
–Are acquired through horizontal gene transfer (i.e., movement of genetic material between organisms, not through transmission of DNA from parent to offspring)
–Carry virulence genes
–Present in pathogenic strains
–Different G+C content from host chromosome
–Occupy large chromosomal regions (10-100 Kb)
–Compact distinct genetic units, often flanked by direct repeat sequences (DRs), tRNAs, and insertion sequences (ISs)
–Presence of (cryptic) mobility genes
–Unstable, prone to deletion
What are antigenic variations?
mechanism by which bacteria or viruses alter their surface moieties in order to evade host immune response), or phase variation
Involves surface structures such as proteins, LPS, AND capsules
What are the variety of mechanisms of antigenic variation?
slip-strand mispairing
flip-flop (DNA segment inversion)
Recombination of sequence cassettes
Adopt protective niches
Phase Variation Through Slipped-strand Mispairing
- Transcriptional level: 2 strands of DNA homologous sequences. you can have a portion of one strand and another strand slip out and be mutant and therefore the sequence now is going to change. In this sequence now, all of a sudden, the promotor can become activated
- You can have this at the protein level – translational: 2 strands and there’s a slippage of the coding regions and their deletions and all of a sudden, the coding region that is at the top is different because a portion of it has been deleted
Flip-flop Phase Variation of Flagella Proteins in Salmonella Enterica
- HIN and HIA are driving the expression of these genes. When being produced, they turn off FiC.
- In flip-flop phase, there is a recombinant gene called HIN that can bend the DNA and bring the ends of the promoter regions L and R close to each other, and it cuts the DNA at these parts and rejoins them with each other, but in a way that it flips this strand.
- R goes where L was and vice versa, and What happens at the end is that the promoter has been reverted causing an inversion of the RNA sequence, and thus FlJa isn’t made anymore because they’re not in the proper orientation, and thus FLIC can now be made (because FLJa inhibits FLIC and when it’s not made anymore. FLIC can be made)
Antigenic Variation in the Lyme Disease Spirochete
Cassettes of genes in bacteria right next to each other, and if the bacteria bends the DNA and brings these cassettes close to each other so therefore you can get any recommendation of these genes in these cassettes, and rearrangements of these sequences which means some genes that weren’t being made are all of a sudden being made, or vice versa, or the activity of some genes are changed
What is the difference between endo and exotoxins?
Endotoxin - lipopolysaccharide complex associated with the outer membrane of Gram-negatives
Exotoxins - produced inside bacteria and then secreted or released into surrounding medium
–Toxins acting on cell membranes
–Toxins active inside cells
–Super-antigens
How do membrane-damaging exotoxins work?
A. Many bacterial toxins form pores in eukaryotic cell membranes, producing oligomeric rings
B. Other toxins, such as phospholipases, degrade components of the membrane
What are the functions of the different domains of AB Toxins?
–AB toxins go inside the cell membrane.
–Binding domain – B domain allows toxin to bind to the host cell
–A domain – translocation domain. Allows toxin to get inside the host cell to conduct their activities
How does bacteria alter host cell signaling?
•Inject proteins into host cells to subvert the cytoskeleton and signal-transduction pathways:
–Manipulating the cytoskeleton to induce membrane ruffling and bacterial invasion
–Preventing being scavenged by phagocytic cells
–Once inside the host cell, remaining within a vacuole by manipulating host cell vesicular transport system
How do bacteria cells advance?
- Within macrophages, e.g. in typhoid
- Through blood (need to be complement- resistant)
- Within cells, tissues, and organs
What is LPS?
•LPS, also referred to endotoxins, are composed of polysaccharides and lipid A
-Lipid A is the toxic part of LPS, and is made up of really long alpha chains connected to core polysaccharides which in turn are attached to long repeating sugar units called the O side-chain
What is Peptidoglycan?
macromolecule composed of a repeating framework of long glycan chains cross-linked by short peptide fragments
