HRR: nature of microbial pathogenesis bacteria Flashcards
Describe the general structure of bacteria
They’re a bag of stuff surrounded by a cell wall. They’re prokaryotes, meaning they’re single-celled with no nucleus. Their genetic material is typically on one circular chromosome
Describe how bacteria grows and why this is significant
Bacteria grows by binary division, meaning one cell becomes two. Bacterial growth is all about growth of the population. This means infections can rapidly go from mild to life-threatening, and natural selection can occur within hours due to the number of generations made in a short time
Describe obligate anaerobes
Oxygen is toxic to them, as they lack superoxide dismutase and catalase. Instead, they make short-chain fatty acids
Describe facultative anaerobes
Can use oxygen, but often don’t. they start with respiration but switch to fermentation when oxygen is depleted. They can also make short chain fatty acids
Describe obligate anaerobes
Require normal atmospheric oxygen concentrations for normal growth
Describe microaerophilic bacteria
Aerobic microorganisms that prefer low oxygen tensions; they grow best in atmospheres enriched with CO2
describe cell wall structure and components of gram positive bacteria
monoderm with a thick layer of peptidoglycan
describe cell wall structure and components of gram negative bacteria
diderm with a bilayer peptidoglycan; the outer layer contains porins and LPS
describe the cell wall structure and components of mycobacteria
diderm with thin peptidoglycan; outer layer has glycolipids and glycolytic acids that make them very waxy
Gram positive bacteria take on a ___ color, while gram negative take on a ___ color
Purple; pink
Describe differential staining
-Fix
-Add crystal violet
-Iodine treatment aka mordant
-Decolorization (gram positive remains purple, gram negative loses color)
-Safranin stain (gram negative turns pink)
What is the function of peptidoglycan in the cell wall
They’re cross-linked to form peptidoglycan polymers that help hold in all the contents of the bacteria…like Spanx. They provide structural integrity and provide shape
Bacterial cell walls are composed of alternating units of…
NAM and NAG (components of peptidoglycan)
Describe lysozyme and its function
Antimicrobial enzyme and component of the innate immune system that breaks 1,4 beta linkage of NAG and NAM. Present in various secretions in the body such as tears, saliva, milk, and mucus
Describe the general composition of gram-positive cell walls
They contain teichoic acid and lipoteichoic acids. Sugars, cholines, and other molecules can attach to the hydroxyls of ribose or glycerol to provide antigenic determinants. They have a thick layer of peptidoglycan
What is the function of lipoteichoic acid
Anchors the cell wall to the membrane; can also manifest an IL-10 dependent inhibition of CD4 T cell expansion
Describe the general composition of gram-negative cell walls.
They have a bilayer of peptidoglycan embedded in periplasmic gel. Their outer membrane is a phospho-lipoprotein bilayer containing porins. It also contains LPS and confers a strong negative charge
What is LPS
An endotoxin produced by gram negative bacteria that facilitates an acute inflammatory response.
What are the components of LPS
Lipid A: innermost component that confers toxic properties
Core polysaccharide lends strength to the outer membrane
O antigen: confers unique immunological ID
LPS can function as a…
PRR
What is the significance of the negative charge on gram negative bacteria
It protects them from phagocytosis, complement, lysozyme, bile, digestive enzymes, and various antibiotics
Describe the cell wall of acid-fast bacteria
Thick cell wall with a lot of mycolic acids. It’s very waxy and may take of a variable reaction when gram stained. For example, when gram stained the wax may hang on to the pigment and stain gram positive.
In acid fast staining, what are the primary and secondary stains
Carbolfuchsin and methylene blue
What are endospores
Defense mechanism against harsh conditions. Essentially, they protect the microbe from things like heat, radiation, enzymes, etc. they’re metabolically at rest and have a spore made of calcium bound to dipicolinic acid that protects its genomic DNA
When mentioning C diff, we are also referencing…
endospores
Describe capsules
They’re a defense mechanism that keeps bacteria from being engulfed; they can literally slip away from macrophages
What is the K antigen
Capsule
What are PRRs
Members of the innate immune system that are the frontline defense against viruses in tissues
What is virulence
The behavior of a microbe that determines what fraction of those infected suffer morbidity or mortality
Describe adhesins as virulence factors
They bind to specific human host sites and determine tissue tropism, aka where the infection will develop. Strong adhesins correlate with ability to cause infection with low levels of bacteria
Adhesins are found on which structures
Pili or fimbriae
Describe the H antigen
They’re also known as flagella. They use an ATPase-like mechanism for movement. They typically take about 1000 protons per rotation and 7.2 million protons to spin at 100 hz
What is phase variation
Genetic process meant to help evade the adaptive immune response; involves changes to the flagella and/or pili. A big one is the changing of the flagellum in salmonella via a transposon that flips direction every 10k divisions
What are biofilms?
Microbes grow on a surface and then stop, and antibiotics only work on actively growing cells. This can leave a layer of non-active microbes that cannot be killed.
What is quorum sensing
A process that allows bacteria to measure how many other cooperating bacterial cells are nearby; more bacterial cells means more quorum factor means more transcription factor to activate gene expression which results in microbes that manifest traits and behaviors of bioactive molecules
What are siderophores
Bacteria use them to acquire iron; they compete with iron-binding molecules to take iron from the host and bring it to the microbes. This is a public good of bacteria
Describe type II secretion pathway
Found in all bacteria. Requires Sec gene products, ATP, and accessory proteins. Tat primarily secretes the folded proteins.
Describe type I secretion pathway
Proteins are exported directly across both membranes
Describe type III secretion pathway
Act as a molecular syringe that injects proteins into other bacteria or human cells
- describe type IV
acts like a syringe that injects proteins and DNA into other bacteria or human cells
describe type VII
ENP pathway involved in biofilm formation
