Infectious Disease, Microbiology, Bacterial Genetics Flashcards
Transmission: spread by contact with the agent on the infected host or from saliva, discharges on the skin, feces, urine, respiratory or genital secretions
direct transmission
organism shed by host into water, milk, food, air, bedding, dust, equipment; contact with contaminated inanimate objects
indirect transmission
Sources of infectious agents
normal microbiota
infected and diseased host
soil. water, fomites
Parts of infectious disease triangle
Host, Environment, Organism
3 main parts of the bacterial cell envelope
Cell wall, periplasm, inner membrane
Characteristics of bacterial inner membrane
lipid bilayer uptake systems export systems electron transport permeability barrier
Characteristics of bacterial periplasm
viscous, oxidizing environment
contains enzymes catalyzing formation of disulfide bonds
contains proteins participating in small molecule break down of polymers to bite size compounds
Characteristics of bacterial cell wall
peptidoglycan
counters osmotic pressure
What bond links NAG and NAM in the bacterial cell wall
B (1,4) glycosidic bonds (pentapeptide linked to NAM)
Main difference between cell wall of gram positive and negative bacteria
Negative - thin (and has extra outer membrane)
Positive - thick
What colors do gram positive and negative bacteria stain?
Negative - pink
Positive - purple
Describe the outer and inner leaflets of the outer membrane of gram negative bacteria
Outer leaflet of outer membrane = Lipopolysaccharides
Inner leaflet = phospholipids
What are the 3 components of LPS?
O-antigen
Core
Lipid A
most abundant molecule on the surface of gram neg bacteria
LPS
what is the toxic region of LPS
Lipid A
What is the purpose of a bacterial capsule
protection, immune evasion
what is the shape of the bacterial genome
double stranded DNA, helical, supercoiled, forms a circle
the bacterial genome is (haploid/diploid)
haploid
circular DNA molecules capable of autonomous replication
plasmids
In bacteria, DNA replication in (unidirectional/bidirectional) from a single origin of replicaiton
bidirectional
Operon
have the same promoter, all genes transcribed as one block (ex. one promotor, one transcriptional start site, 3 open reading frames, 3 proteins produced from one mRNA)
regulon
promoter binds the same regulatory factors which allow genes to be expressed at the same time and/or under the same conditions even though they are not physically close to one another on the genome
Translation is initiated by the binding of the (30S/50S) subunit to the ribosome binding site on the mRNA
30S
3 sites of the 50S subunit
A (acceptor)
P (peptide)
E (exit)
4 ways bacteria acquire new DNA material
Natural transformation (uptake of naked DNA)
Conjugation (transfer of plasmid DNA from one bacterium to another)
Transduction (infection by bacteriophage)
Acquire genes that specify antibiotic resistance genes, genes encoding virulence factors (e.g. toxins)
To cause disease a bacteria must
Interact with host surfaces
Avoid clearance by the host
Acquire nutrients to grow
What are 3 ways bacteria interact with host surfaces
adherence
biofilms
invasion
2 requirements for adhesion
adhesin (binding entity on bacterium) cognate receptor (binding molecule on host surface)
obstacle to adhesion
both surfaces negatively charged
3 major types of adhesin-receptor interactions
Lectin-carbohydrate (bacterial adhesin is the lectin in most cases)
Protein-protein (fibronectin, integrins)
Hydrophobin-lipid (hydrophobic region of protein adhesin interacts with lipids)
major types of bacterial adhesin (initial)
pilus
fibrillar surface proteins
major type of bacterial adhesin (intimate)
integral membrane adhesin
communities of microorganisms encased within an extracellular polymeric matrix and living on a surface
biofilm
rational for biofilms ability to protect against toxic environment
bacteria on periphery are killed, cells in the middle are protected
ability to gain entry inside host cells, allows bacteria to cross physical barriers, hide from the immune system, disseminated from the site of infection
invasion
general strategy for invasion and the two main mechanisms
General strategy: rearrangement of actin cytoskeleton
Mechanisms: zipper, trigger
Invasion - zipper mechanism
activation of membrane-located host cell receptors by invasion factor(s) on surface of bacteria - receptors are ALREADY present on surface of host cells
__________ and accumulation of more receptors lead to engulfment of bacteria by zipper-like mechanism
invagination
invasion - trigger machanism
requires injection of bacterial proteins into the cytoplasm of host cell
Type Three Secretion System (TTSS)
common and well-characterized injectisome system
in TTSS trigger mechanism, bacterial effectors subvert eukaryotic signaling pathways, rearranging actin to form _________ that will engulf bacteria
pseudopods
Main ways bacteria avoid clearance by the host
Antigenic variation (changing antigens and epitopes)
Phase variation (turn-off production of a protein)
slgA protease (prevents trapping of bacteria in mucus bathing mucosal surfaces)
Capsule
Interference with complement cascade (C5a peptidase)
2 ways bacteria can survive in host cell
Cytosolic and Intravacuolar (in both, protected from antimicrobial content of lysosome)
Characteristics of a bacterial capsule (4)
Antiphagocytic
Host mimicry
Sheild (stealth mode)
Prevents activation of complement cascade
Why is acquiring iron an issue for bacteria?
It is one of the most abundant elements in nature BUT… it is insoluble under physiologic conditions and sequestered in animal hosts
Bacterial solutions for acquiring iron
Receptors for host iron binding proteins
Siderophores (high affinity for iron)
