Pathogens Flashcards
What are the classifications of microbes
Eukaryotes (organelles)
Prokaryotes (no organelles)
Acellular organisms (non living)
Why are microbes important
They make up global ecosystems
They are saphrophytes
They are used in economic biotechnology
They can be nuisances
They can be pathogenic
Describe the bacterial genome
Located in the cytoplasm
Comprises the single circular chromosome and plasmid
Dictates metabolic and biosynthetic capacity
Bacteria with _____ genomes tend to have ____ fastidious growth requirements
Larger, less
What are the 3 types of mutations and what could they lead to
Point, insertions, deletions»_space; gain or loss of function
What are the 3 methods of DNA exchange
Transformation - uptake of free DNA
Conjugation - transfer of DNA by direct cell to cell contact
Transduction - transfer by bacteriophage
Describe the plasma membrane
Semi permeable Lipid bilayer - maintains homeostasis
Site of ATP generation
Range of transport proteins
What are endospores
Complex intra-cellular structure formed during replication of certain bacteria when growth conditions are poor
Resistant to temp, desiccation, radiation, chemical agents, enzymes etc.
Visualised by -ve staining
Cause deep tissue infections
Describe the chemical component cell wall is made of
Made of peptidoglycan
Polymer of NAM and NAG
Protects against osmotic pressure
Crosslinks can be inhibited by beta-lactam antibiotics
Describe the structure of gram positive cell walls
Thick peptidoglycan layer - molecules diffuse through interbridge gaps
Embedded in teichoic acids - attachment
Simple systems to secrete proteins
Describe the structure of gram negative cell walls
Thin peptidoglycan layer
Outer, non energised membrane - porins = transfer of molecules across / lipopolysaccharides = attachment
Molecules diffuse through peptidoglycan
Tightly regulated mvmt across PM
Many varied complex systems to secrete proteins
What is the clinical relevance of gram staining
Reveals bacterial shape and arrangement
What is different abt the cell wall of mycobacterial species
It has outer lipid layer, mycolic acids, arabinogalactan, and peptidoglycan
Detected using acid fast staining
What is flagella
External structure of bacteria
Complex structure required for bacterial chemotaxis (mechanism for bacteria to move towards nutrients or away from toxins)
Number and arrangement varies
What are fimbriae/pili
External structure
Hair like protein chains
Virulence factor - involved in attachment (to other cells or surfaces)
Mechanism for DNA transfer (conjugation) - connects bacteria and then retracts which allows for transfer of antibiotic resistance genes
What is the capsule
External structure
Polysaccharide layer beyond the cell wall
Found in both gram +ve and gram -ve
Protection from desiccation and phagocytosis
Adhesion to cells/surfaces
Can be visualised through a negative capsule stain which stains in the inside but not the capsule creating a halo effect or through transmission electron microscopy which is where the negative capsule binds to positive gold particles
what are commensal bacteria
colonise all surfaces of host
several benefits > metabolic / protection against pathogens by competing for colonisation sites
how are some pathogens also commensal
they are commensal but become opportunistic (pathogenic) in response to immunological insult such as tissue damage > provide access to deeper tissues to access more nutrients
what are primary pathogens
provide no advantage to host
not part of normal microbiome
damage the host
egg E.coli > secrete toxin
what are pathogens
disease causing agents
damage can be indirect (ie disturbs metabolic balance or nutrient acquisition) or directly (ie toxins)
structural and non structural features contribute to…
mechanism of disease (pathogenesis) and capacity to cause disease (virulence)
these allow for competition to establish infection and damage the host and cause symptoms
outline the pathogenic cycle
transmission > colonisation > proliferation > evasion > repeat
what are some transmission routes
direct contact e.g bites or wounds
indirect contact via fomites (contact w contaminated objects) > important route for Nosocomial infections
airborne
faecal-oral
food borne
zoonotic
what is ID50
infectious dose - number of bacteria needed to infect 50% of individuals
what is inoculum size
amount of pathogens an individual is actually exposed to
what is the relevance of extracellular enzymes released by bacteria
role in pathogenesis
e.g beta haemopysin is a secreted phospholipase which ha a distinct phenotype on blood agar
what are exotoxins
proteins made and secreted during bacterial growth
toxic at low doses
categorised by site of activity
two groupings = cytolysins (cause lysis) and two-component toxins (disrupt cellular processes)
what are endotoxins
bacterial structural components that have toxic activity
released on death of bacteria (meaning sometimes taking antibiotics can actually make it worse)
what are some host factors that affect outcome of infection
age, immune status, prior exposure, diet
what are outcomes of infection
clearance
asymptomatic carriage
symptomatic carriage
what factors are related to disease patterns
timing (acute, chronic, latent)
location (local, systemic)
what is an example of a bacterial pathogenesis
L.monoctyogenes - gram postive, motile
> food borne zoonosis
incubation ~3 weeks
secretes several toxins
by which process do bacteria grow
binary fission
what are the four phases of bacterial growth
lag phase
exponential phase
stationary phase
death phase
what happens in the lag phase of growth
adapt to new conditions, enzymes and new metabolites accumulate
what happens in the exponential phase of growth
maximum constant growth rate
what happens in the stationary phase of growth
oxygen and nutrient demands cannot be met > death rate = growth rate
what happens in the death phase of growth
death rate > growth rate
what factors affect bacterial growth
nutrient availability, O2 availability, pH, temperature, osmolarity
what are the oxygen requirements of obligate aerobes
require o2
what are the oxygen requirements of strict anaerobes
cannot survive in o2
what are the oxygen requirements of facultative anaerobes
more efficient with o2 but can still metabolise via fermentation when absent
what are the oxygen requirements of aerotolerant anaerobes
unaffected by presence of o2
what are the oxygen requirements of microaerophiles
require a specific o2 concentration
what are chemotherapeutic agents
chemical agents used to treat disease
kill or inhibit growth of pathogenic microbes
what are the primary mechanisms/classes of actions
inhibitors of cell wall synthesis
protein synthesis inhibitors
metabolic antagonists
nucleic acid synthesis inhibtion
what does bacteriostatic mean
inhibits growth
what does bactericidal mean
kills the bacteria
describe inhibitors of cell wall synthesis
e.g penicillins
binds to proteins involved in peptidoglycan assembly
inhibition of last step in bacterial cell wall synthesis
prevents crosslinkage of peptidoglycan strands > lysis
acts on GROWING bacteria
describe protein synthesis inhibitors
e.g aminoglycosides
either bind specifically to prokaryotic ribosome and interfere w function or inhibits stage of protein synthesis
describe metabolic antagonists
e.g sulfanomides
interfere w enzymes involved in folic acid synthesis (unable to construct basic building blocks for nucleic acids)
selectively toxic for bacteria
describe nucleic acid synthesis inhibition
e.g quinolones
block DNA replication
block transcription
not as selectively toxic
where can antibiotic resistance genes be found
bacterial chromosomes
plasmids
transposons (mobile genetic elements)
interns (gene capture system)
through what mechanisms can antibiotic resistance genes be spread
through transformation, conjugation, transduction (rare)
how do antibiotic resistance genes spread
acquisition of resistance genes from mobile genetic elements such as plasmids, transposons etc
what are resistance plasmids
can carry multiple antibiotic resistance genes
usually transferred to other cells by conjugation or transformation
carry transposons that encode antibiotic resistance
what are composite transposons
contain genes for antibiotic resistance
within a cell - rapidly move b/w chromosome and plasmids
b/w cells - can move thru a bacterial popn
what are gene cassettes
sets of resistance genes
can be part of transposons, interns, or located on bacterial chromosome
what are integrons
gene capture system > capture an expression of genes and gene cassettes
mechanism for accumulating antibiotic resistance genes in bacteria
what can be done to prevent antibiotic resistance
give antibiotics in high concentrations
give two antibiotics at once
don’t give antibiotics unless necessary
possible future solutions - dev of new antibiotics and use of alternative therapies e.g bacteriophages
describe the diagnostic schema
symptomatic patient > signs and symptoms > presumptive clinical diagnosis > specimen collection > select tests > results and interpretation > definitive diagnosis > treatment options > if patient is now asymptomatic then successful, if not, then reevaluate signs and symptoms
what is an example of a genetic test in detection and identification of bacteria
real time PCR
> amplified targets fluorescently tagged > relative fluorescent units plotted in real time hence no need for gel electrophoresis
what is an example of a serologic test in the detection and identification of bacteria
rapid immunoassay (RIA)
> relies on monoclonal antibodies (mAbs)
- capillary flow moves antigen > specific interaction b/w mAb and antigen > binding at test line results in colour change > control mAbs confirms RIA validity
indicative rather than definitive
why are multiple tests used in the process of detecting and identifying
to account for variability in sensitivity and specificity
what is an example of culturing in detection and identification of bacteria
agar plates
> selective = allows for growth of selected groups of bacteria
> differential = allows growth of a number of types of bacteria w defined characteristics
utilise agar medium elevate to specific bacteria
what is an example of a biochemical test in detection and identification of bacteria
catalyse assay
> h2o2 is a by-product of metabolism > breaks down to o2
if o2 gas generated then catalase positive
what are different types of microscopy in detection and identification of bacteria
gram stain
acid fast stain
spore stain
describe gram stain in detection and identification of bacteria
gram -ve = transparent after alcohol decolourising
gram +ve = purple
describe acid fast stain in detection and ID of bacteria
non acid fast = transparent after alcohol decolourising and then blue after counterstain
acid fast = pink
what is an example of an analytic method in detection and ID of bacteria
mass spectrometry = peaks release to specific molecules, pattern to specific bacteria