Microbiology and Infection Flashcards
What are Bacteria
Single celled microbes
Prokaryotic
No nucleus
Have no membrane bound organelles
Instead have a single loop of DNA contained in the nucleoid
Plasmids?
Grouped according to different factors
-shape
-microscopic arrangement and look
-groups based on gram reaction
-cell structure
What are the different shapes?
Cocci
Rod
Spirilla
Vibrios
Spirochaetes
What is Cocci and Bacilli
c0cci- the joined up balls
bacilli- chains of bacilli/rods etc
What are the two groups based on gram reaction?
Gram positive - purple or blue
Gram negative - pink or red
Based upon cell structure
Gram Stain process
step 1- Crystal violet, stains cell purple or blue (primary stain)
step 2- iodine, mordant makes dye less soluble so adheres to cell walls
step 3- alcohol, decolorizer washes away stain from gram negative stains. Gram positive cells remain purple/blue
gram negative are colourless
step 4- safranin counterstain allows dye adherance to gram negative cells, gram positive cells remain blue/purple
gram negative cells appear pink/red
molecules or cellular structures that enable bacteria to successfully colonize a host, evade its defenses, and cause disease
Bacterial virulence factors e.g
plasmid
endotoxins
exotoxins
flagellum
fimbriae
Plasmid
Additional circular DNA
Obtained by gene transfer
Can confer extra genes
Virulence to overcome defences
Antibiotic resistance
Unique metabolism
Endotoxin
Found in Gram negative cells
Also known as lipopolysaccharides
Composed of a lipid and an O antigen
O antigen brings about a strong immune response
Can lead to septic shock
Inflammatory mediators
Reactive Oxygen Species (ROS)
Exotoxin
A toxin which causes damage to the host
Destroying cells
Disrupting metabolism
Can be secreted or released during lysis
Effect can be localised or systemic
Different classes
Cell surface active
Membrane damaging
Intracellular
Matrix damaging
Exotoxin, active cell surface
Superantigens
Found in Staphylococcus aureus and Streptococcus pyogenes
Causes Toxic Shock Syndrome
Binds protein on immune cells leading to increased activation of immune system
Causes fever, vomiting, liver inflammation, kidney failure
Extoxin: membrane damaging
Channel forming
Cytolysins
Create pores in the host cell membranes
Small molecules from within the cell leak out and water leaks in to retain osmotic pressure
Causes blebbing
Loss of molecules can interrupt protein synthesis and cell signalling
Enzymatically active toxins
Example is in Clostridium perfringens
Produces a phospholipase
Hydrolyses phospholipids such as those in cell membranes
Causes destruction and lysis of the cell
Causes gas gangrene
AB toxins
Cholera
Comprised of 2 types of subunits A and B
A1B5
Binds to the cells of the small intestine
Enters the cell and triggers a receptor which opens the CFTR pump (Flood of chloride ions causes an efflux of water which hydrates the mucus and aids in it’s removal.)
Antibiotics
Used to treat bacterial infections
Classified in several ways
By the target of action
By chemical structure
By overall function
By specificity
Bacteriocidal
Target the cell wall: penicillins and cephalosporins
Target the cell membrane: polymyxins
Target bacterial enzymes: rifamycins, quinolones and sulfonamides
Bacteriostatic
Target bacterial protein synthesis: macrolides, lincosamides and tetracyclines
Bacteria become quiescent and are eventually removed by detoxification mechanisms
Can also be classed based on specificity
Can be ‘narrow range’
Effective only against a small specific group of bacteria
Can be ‘wide range’
Effective against a much broader range of bacteria
Yersinia pestis
Causes plague
Historically known as The Black Death
There have been other outbreaks but none so great as The Black Death
75-200 million deaths between 1347 and 1351
There are 3 main forms of plague and 2 minor forms
Plague
Bubonic plague: cause bubos in lymph nodes
Septicemic plague: infection is found in blood stream and cause tissue necrosis
Pneumonic plague: infects the lung tissue causing tissue necrosis
Pharyngeal plague: affects the tonsils
Meningeal plague: causes meningitis
Symptom of plague- Bubos
Bubos
Swollen lymph nodes caused by haemorrhagic inflammation
Tissue necrosis (acral necrosis) [septicaemic
Pneumonic tissue necrosis
Viruses
Small infectious particle
Many different sorts
Can infect every life form
Sometimes not defined as an organism
MRS GREN
Needs another cell to be able to replicate and grow
When not inside a host cell they are called virions
Basic Structure of Virus
Genetic material
Capsid: protein shell (different types)
Envelope: lipid coating
Stages of Viral Replication
Attachment: virus binds to a specific site on a cell
Penetration: either injects or is endocytosed
Uncoating: removal of envelope and capsid
Replication: uses cells replication machinery
Assembly: uses cells protein synthesis machinery to assemble new viral particles
Release: causes cell lysis and release of new phage
Effect on host cells
Effects are called cytopathic
Varied effects
Normally results in cellular death
Cell lysis during viral release
Induced apoptosis
Cell cycle suppression
Vaccination
Designed to stimulate a persons immune system
Develops adaptive immunity which can then be used during normal encounters with a virus
4 methods of Vaccination
Inactivated
Attenuated
Component
mRNA
inactivated
uses whole viral particles but has been completely deactivated.
attenuated
use whole viral particles but has been completely deactivated
