Microbiology Flashcards
what is microbiology?
the science of microrganisms
what are microorganisms?
organisms that are too small to be seen with the unaided eys
what are the major groups of microbes?
bacteria
fungi
parasites
microalgae
viruses and prions(infective agents)
what is the general order of size of microorganisms?
moulds>protozoa>yeasts>bacteria>viruses>prions
microorganisms can be cellular or acellular, what do these mean?
cellular- formed by cells
acellular- without a cellular structure
what are the two types of cellular microorganisms?
monocellular (single cell)
pluricellular (more cells)
what microorganisms fall under the cellular structure?
fungi and protists (eukaryotic)
bacteria and archea (prokaryotic)
what microorganisms fall under the acellular structure?
viruses (protein and nucleic acids)
prions (proteins)
what are the features of bacteria?
prokaryotes
mostly unicellular
what are the features of fungi?
eukaryotes
unicellular and pluricellular
what are the featires of parasites?
eukaryotes
unicellular and pluricellular
what are the features of microalgae?
mostly eukaryotic
both unicellular and pluricellular
what are the features of viruses?
acellular
small infectious partic;es
they need to infect a cell to replicate their particles
what are the features of prions?
acellular
simpler infectious particles made up of only proteins
what use do microbes have for life on earth?
organic waste decomposition
production of food
drugs/enzyme synthesis
digestion and molecule generation
oxygen generation
nitrogen fixation
what is normal microbiota?
microbes are present in and on the human body
how can normal microbiota be helpful?
prevent growth of pathogens
produce growth factors
breaking down toxic molecules, boosting the immune system and antimicrobial chemicals
what name is given to a round bacteria?
coccus
what name is given to a rod shaped bacteria?
bacillus
what name is given to a curve rod shaped bacteria?
vibrio
what name is given to an oval shaped bacteria?
coccobacillus
what name is given to a rigid spiral shaped bacteria?
spirillum
what name is given to a flexible spiral shaped bacteria?
spirochete
what is the name if a bacteria has many shapes?
pleomorphic
what are the different arrangements of bacteria?
pairs
clusters
chains
tetrads
what are the rules of naming species of living things?
each organism has two names: the genus and the species epithet
both are written in italics
genus is always capitalised
epithet is lowercase
genus name can be abbreviated
what are the rules of naming species of living things?
each organism has two names: the genus and the species epithet
both are written in italics
genus is always capitalised
epithet is lowercase
genus name can be abbreviated
what is the composition of the plasma membrane?
fluid mosaic model similar to the eukaryotic cells
40% lipids 60% proteins
lacking sterols (cholestrol of human cells)
contain sterol-like molecules (hopanoids)
what are the functions of the plasma membrane?
serves as a selectively permeable barrier
controls movement of molecules across the cells
plasma membrane infoldings, mesosomes
site for DNA replicarion and cellular respiration
what are the functions of the cell wall?
maintain bacterial cell integrity and shape
prevents the cell from bursting when water flows into the cell by osmosis
can contribute to pathogenicity (ability to cause disease)
what is the important evidence of the cell wall?
only a few bacteria do not posses cell walls
target of many antibiotics
what is the composition of the cell wall?
structural difference between these two groups gram + and gram -
what is the composition of peptidoglycan?
a rigid multi-layered network made up of linear chains
each chain is a polymer of a repeating identical disaccharide unit (made up of the following 2 monosaccharides: NAG and NAM) in long rows
a tetrapeptide chain of 4/5 amino acids is linked to NAM
chains are linked by peptide cross bridges betwee tetrapeptide side chains of NAMs
what is the formation of peptidoglycans?
peptidoglycan subunit (NAG/NAM) –> repititions of peptidoglycan subunits form individual chains –>transpeptidation reaction
what is the structure of a gram + bacteria cell wall?
thick layer of peptidoglycan
thin periplasmic space
plasma membrane
also contain teichoic acids made up of an alcohol and a phosphate group which s used to bind and regulate movement of cations into cell, regulate cell growth and prevent cell lysis, lonked also to the cell membrane
what is the structure of the gram - bacteria cell wall?
thin peptidoglycan layer
periplasmic space
outer membrane:
-phospholipid bilayer
-lipopolysacharides
-porins
-lipoproteins
what is the function of the outer membrane in the gram -?
evade phagocytosis and immune system
permeability barrier to antibiotics, f=digetive enzymes etc.
what is gram staining used for?
to distinguish groups of bacteria according to their cell wall structure
staining: for better viual observations to highlight differences
what are the steps in gram staining?
- primary staining- crystal violet
- mordant application- iodine treatment
- decolourisation
- counterstaining- safranin
what colour would gram + end up after gram staining?
purple
what colour would gram - end up after gram staining?
red
what are the gram + principles of gram staining?
alcohol dehydrates peptidoglycan forming crystals inside and the dye is retained
what are the gram - principles of gram staining?
alcohol dissolves outer membrane and leaves holes in peptidoglycan
crystal violet-iodine complex washes out = cells are colourless
safranin (pink) added to stain cells
what are the components external to the cell wall?
glycocalix:
can be either a capsule(thick, well organised) or slime layer (thin, unorganised)
flagella: sensoru organelle, propel bacteria (using ATP)
fimbrae: thin allow for attachment
sex pili:DNA transfer from one cell to another
what are the functions of the glycocalix?
confer pathogenity
prevet phagocytosis
avoid desiccation by preventing water loss
aid in attachement to solid surfaces
what are the steps of baceria cell cycle/ division?
1) cell elongates, enlarging its volume and DNA is replicated
2) cell wall and plasma membrane begin to constrict
3) cross-wall forms, completely seperating the two DNA copies
4) cells separate
THIS IS BINARY FISSION another way is budding
what are the phases of bacteria population growth?
1)lag phase
2)log phase
3)stationary phase
4) death phase
what happens at the lag phase?
intense activity preparing for population growth, but no increase in population
what happens in the log phase?
logarithmic or exponential increase in population
due to reproduction by binary fission or mitosis
what happens at the stationary phase?
period of equilibrium
microbial deaths balance production of new cells
what happens in the death phase?
population is decration at a logarithmic rate
what is the equation for total number of cells after generation time?
Total number of cells =
N0 x 2^number of generations
where N0 is the initial cell number
what are biofilms?
microbial communities
form slime or hydrogels that adhere to surfaces
bacteria cell-cell communication
share nutrients
shelter bacteria from harmful environmental factors or microbiocides
what are the physical requirements for bacterial growth?
temperatire
pH
osmotic pressure
what are the chemical requirements for bacterial growth?
carbon source
organic growth factors
nitrogen, sulphur and phosphate
ions, trace elements
oxygen
what are the names given to different bacteria based on optimum temperature?
psychrophiles (cold-loving)
psychrotrophs (20-30)
mesophiles (25-40)
thermophiles (50-60)
hyperthermophiles (>80)
why is preservation temperature important?
control of temperature is essential for the storage of parmaceutical products and food
what are the names given to different bacteria based on optimum pH?
neutrophiles (6.5-7.5)
acidophiles (0-5)
alkalophiles (8-11.5)
what does a hypertonic (higher in solutes inside the cell) enviornment cause?
plasmolysis
due to high osmotic pressure
what are the classifications of microorganisms based on their oxygen requirements?
obligate aerobes
facultative anaerobes
obligate anaerobes
what are obligate aerobes?
require oxygen to live
what are facultative anaerobes?
can grow via fermentation or anaerobic respiration when oxygen is not available
grow best in aerobic conditions
what are obligate anaerobes?
do not tolerate oxygen and are harmed by it
what is a culture?
microbes growing in/on culture medium at appropriate conditions
what is a culture medium?
nutrients prepared for microbial growth in a labratory
what does inoculum mean?
introduction of microbes into a medium
what are the features of agar?
complex polysaccharide
used as a solidifying agent for culture media in petri plates
generally not metabolised by microbes
what is selective media?
suppress unwanted microbes and encourage desired microbes
what is differential media?
allow distinguishing of colonies of different microbes on the same plate
what is enrichment culture?
encourages the growth of a desired microbe by increasing very small numbers of a desired organismsm to detectable levels
how is it possible to obtain a pure culture?
individual organisms must be isolated
streak-plate method is commonly used
why is aseptic technique critical when isolating microorganisms?
procedures under suitably controlled conditions to maintain the sterility, free from external sources of contamination
what are the steps of isolating microorganisms?
1) loop is sterilized
2) loop is inoculated
3) first set of streaks is made
4) loop is steralized
5) second set of streaks are made
6) loop is steralized
7) first set of streaks made
8) isolated colonis develop after incubation
what is the streaking technique?
a sterile loop is inserted into a sample and streaked onto a plate in a pattern to obtain individual colonies
what is colony formation?
a population of cells arising from a single cell
what is direct measurment of microbial growth?
rely on light microscope and a cell counter
plate count
filtration
direct microscopic count
number of bacteria=number of cells counted/volume of area counted
what is indirect mesurment of microbial growth?
turbidity (mass)
metabolic activity
cell mass (dry-weight)
how do we ensure the right amount of colonies are counted in the sample?
the original inoculum must be diluted via serial dilution
what is the equation for serial dilution?
number of colonies on the plate x reciprocal of dilution of sample= number of bacteria/ml
what are endospores?
resting/dormant/ inert form of some bacterial cells
produced only by two Gram + genera: bacillus and clostridium
what are endospores used for?
it is a mechanisms for survival to adverse environmental conditions that would be lethal for the bacteria
▪ e.g. nutrients depletion,
▪ environmental stresses (extreme temperature, pH),
▪ chemical stresses (antibiotics, disinfectants), etc
what is sporulation?
endospore formation
what is germination?
endospore returns to vegitative state
when does sporulation normally start?
when growth ceases due to lack of nutrients or evironmental stress (activating a set of genes to induce this differentiation and quenching genes involved in the germinative life of bacteria)
what is the structure of an endospore?
an endospore has an ovoid shape and a multi-layered structure which contains a core
what is contained within a core of an endospore?
containing DNA, ribosomes, essential proteins and a large depots of calcium dipicolinate
what structures are surounding the core of an endospore?
▪ Core walls: innermost layer
▪ Cortex: made of peptidoglycan
▪ Spore coat: fairly thick, and impermeable layer.
It confers resistance to chemicals/antibiotics
▪ Exosporium: thin covering, not always present
what are the three steps in germination?
activation (usually heating to damage the spore coat)
initiation
outgrowth
whats the difference in structure in a vegitative cell and an endospore?
vegitative= typical gram-positive cell, a few gram negative
endospore= thick spore cortex, spore coat, exosporium
how can endospores be used as a weapon for bioterrorism?
some spore forming bacteria are capable of causing diseases
what type of resistance does an endospore have?
extroadinary resistance to desiccation, heat, chemicals and radiation in comparison to the vegetative bacteria
which make endospores difficult to eliminate
which cause issues in a clinical setting or in aseptic situations
what is sterillisation?
destroying all microbial life (including endospores)
what is disinfection?
reduces the number of pathogenic microorganisms (not endospores)
what is sanitisation?
reduces the microbes to safe levels by public health standards
what is antimicrobial chemotherapy?
drug treatment for specific infections used internally to selectively kill or inhibit growth of microorganisms within the host tissues, targeting a unique structure of the specific microbe
where do you use disinfectants?
agents applied on inanimate objects/surfaces
where do you use antiseptics?
agents applied on living tissue
what us the goal of any sterilisation process?
the destruction of bacterial endospores, viruses and cellular organisms
prevent infection, food/ environment/ pharmaceutical spoilage
what is the 3 most resistant bacteria?
prions
endospores of bacteria
mycobacteria
what are the 3 least resistant bacteria?
viruses with lipid envelopes
gram-posistive bacteria
viruses without envelopes
how woulod you describe the rate of microbial death?
death of the whole population is not instantaneous
death continues ina logarithmic manner as the time or concentration is increased
what are the effectiveness of the control agents in the treatments to control the microbial death depend on?
time of expoure
microbial characteristics
number of microbes
environment
what are the effects on the microbes treatment to control the microbial death depend on?
alternation of membrane permeability
protein denaturation
damage to nucleic acids
what are the physical treatments to control the microbial death?
temperature
filtration
radiations
osmotic pressure
what are the chemical treatments to control the microbial death?
alcohols
halogens
iondine
chlorine
phenolics
aldehydes
quaternary ammonium compounds
sterilizing gases
heavy metals
what is the use of elevated temperature(> Max temp)?
to kill microbes
what is moist heat?
hot water, boiling water, or steam between 60 and 135 degrees
kills microbes by denaturing their proteins
what is dry heat?
hot air or an open flame, which ranges from 160 to thousands of degrees
kills microbes by denaturing the cell, and oxidation effects
which is more effective, moist or dry heat?
moist heat
what are the two ways to get moist heat?
autoclave
paturisation
what is an autoclave?
preffered sterilisation method, unless material is damaged by heat, moisture or high pressure
closed chamber with hot saturated team under pressure
steam must directly contact the material
what is pasteurisation?
moist heat disinfection
used to reduce microbes respnsible for spoilage of beer , milk, wine and juices…
except for UHT, pasteurisation does not sterilise
what are the 3 methods of pasteurisation?
▪ Classic Method of Pasteurisation: 65 o C for 30 minutes
▪ Flash Pasteurisation (HTST): Used today. 72 o C for 15 seconds
▪ Ultra High Temperature Pasteurisation (UHT): 140 o C for 4 seconds and then cooled quickly in a vacuum chamber. This is a sterilising method
what is the use of cold temperatures in microbial growth?
slow down microbial growth
reduces metabollic rate of most microbes to stop their proliferation and toxin productio , but do not kill microbes
what is filtration?
removal of microbes by passage of a liquid or gases through membrane material with defined small pores
what is osmotic pressure?
the use of high concentrations of salts and sugars in food is used to increase the osmotic pressure and create a hypertonic environment
what is plasmolysis?
as water leaves the cell, plasma membrane shrinks away from cell wall. cell may not die, but usually stops growing
what does ultraviolet light radiation do to a microbe?
damages microbial DNA
has poor penetration power
used only for surface sterillisation
what does ionising radiations do to a microbe
produce reactive free radicals that lead to microbial cell death
high penetrating power
used to irradiate pharmaceutical and disposable medical supplies, foods and other heat-sensitive items
what factors influence the efficacy of a given chemical agent?
the kinds of organisms present
degree of contamination
time of exposure
nature of the material being treated
concentration of disinfectant
what are some commercial disinfectants and antiseptics?
alcohols
iodine
chlorine
what type of aldehyde has a sterilising power?
glutaraldehyde (sterilise medical equiptment)
what type of gas has a sterilising gas?
betapropiolactone (sterilise heat-sensitive material in an autoclave)
what is antimicrobial chemotherapy?
administration of specific drugs to treat infectious disease, having selective toxicity against pathogens involved in infectious, not host cells
▪ Antibiotics →bacterial infections
▪ Antiviral drugs →virus infections
▪ Antifungal drugs →fungal infections
▪ Anthelminthic drugs →worm infections (parasites)
▪ Antiprotozoal drugs →protozoan infections (parasites)
what is selectivity?
take advantage of the difference between the structure of the bacterial cell and the hosts cell
what is symbiosis?
close interaction between two organisms of different species
what are the three sybiotic relationships?
mutualism
commensalism
parasitism
what is mutualism?
both species benefit from their interactions
what is the benefit to the bacteria in mutualism?
they have a place to eat, survive and multiply
what are the benefits to humans in mutalism?
bacteria aid digestion
breakdown food that the host cannot normally digest and producing vitamins
what is commensalism?
one partner in the relationship benefits
the other neither benefits nor is harmed?
what is the benefit to bacteria in commensalism?
acquire nutrients consuming dead skin and a place to live and grow
commensal bacteria may become pathogenic and cause disease
what is parasitism?
one partner, the pathogen, harms the host, causing infectious disease
what is the benefit to bacteria in parasitism?
virus takes advantage of the translational machinery of the cell to replicate virus particles
what are viruses?
obligate intracellular parasites
what is the harm to human cells in parasitism?
viral infections lead to the death of the cells and tissue damage
what is microbiota?
all the microorganisms that live in and on an organism
what are the features of microbiota?
approximately 10^11 organisms
1-3% tatal body mass
generally non-pathogenic
symbiotic with host
when does microbiota begin?
at birth
what different exposure of microbiota is given through vaginal birth and a caesarean delivery?
vaginal delivery- from mothers birth canal
caesarean delivery- exposure from initial caretakers
what are important colonisers of the gut?
bifidobacteria
can ferment sugars found in human breat milk provides the infant with calories and lowers the gut pH, limiting growth of pathogens
when does microbiota in a human reach an adult-like composition?
age 3
what factors determine the distribution and composition of normal microbiota?
nutrients
physical and chemical factors
hist defences
mechanical factors
what internal organs and tissues are normally free of microorganisms?
brain
blood
cerebrospinal fluid
muscules
what are the functions f the human microbiota?
dietery fibre fermentation into short chain fatty acids (source of energy, turns into CoA)
synthesis and excrete vitamins
prevent colonisation by pathogens
stimulate the developemnt of certain tissues
immune system stimulation/maturation
regulate inflammation
modulate and affect the central nervous system
what is dysbiosis?
an imbalance of microbial species and a reduction in microbial diversity within certain bodily microbiomes
what can dysbiosis be caused by?
dietary changes
antibiotic use
psychological stress
physical stress
what types of diseases can dysbiosis lead to?
inflammation
what is an opportunistic infection?
infection caused by commensals that do not cause diseases in a healthy host but in some circumsatnces can become an opportunistic pathogen
what are probiotics?
live microrganisms, which, when administered in adequate amounts, can restore the normal balance of microbiota and related benefcial functions, conferring a health benefit to the host
what are prebiotics?
compounds added to enhance the colonisation and positive health benefis of probiotic microbes
what are synbiotics?
foods or supplements that include both a prebiotic and a probiotic
what is a pathogen?
any organism that causes disease
what is an opportunistic pathogen?
may be part of normal microbiota and causes disease when the host is immunocompromised or when they have chance to outgrowth
what is pathogenicity?
ability of a pathogen to cause disease
what is virulence?
degree of harm inflicted on its host
what are the steps in pathogenesis of bacterial infections?
- Entry of pathogens into the body
Any organism that causes disease according to the transmission routes (e,g.
penetration, inhalation, ingestion and introduction into the blood) - Attachment of the pathogen to some tissues
- Multiplication
- Invasion/spread of the pathogen
- Evasion if the host defences/immunity
- Damage to the host tissue(s)
what are the steps in the entry, adherance,colonisation and invasion of pathogens in bacterial infections?
- Entry into the host
▪ Portal of entry
➢Skin, respiratory, gastrointestinal, urogenital
systems, or conjunctiva of eye - Attachment of microbe to specific target cells (highly
specific and permanent or nonspecific and reversible)
▪ Adherence structures:
➢Pili
➢Fimbriae
➢Glycocalyx (Capsule) - Colonisation—establish a site of microbial replication
on or within host - Invasion (active or passive)
▪ Active - occurs through production of lytic substances that alter host
tissue
➢E.g. pathogens that induce the disruption of the intestinal lining
▪ Passive – host tissue alteration was already present and it was not
caused by the pathogen
➢skin lesions, insect bites, wounds
what are the ways some pathogens sucessfully overcome competition and elude intial host responses as well as the adaptive immune system?
▪ Find shelter to avoid recognition by defence cells.
▪ Survive and replicate inside host cells
▪ Squeeze between host cells.
▪ Avoid phagocytosis (capsule)
▪ Burrow under mucus.
▪ Find shelters within biofilms.
▪ Produce enzymes that inactivate innate resistance mechanisms.
▪ Excrete specialized proteins to selectively kill host cells
▪ Mutate and/or reduce cell surface proteins detected by immune cells
how does the pathogen in bacterial infection damage the host tissue?
- secreting enzymes that degrade host cell for nutrients
- replicating inside the cells and inducing apoptosis of the immune cell
- Toxins – substances that disrupt the normal metabolism of host cells
- Exotoxins
- Endotoxins
- Hypersensitivity reactions - inducing an excessive release of
cytokines by immune cells and exacerbating inflammatory responses,
destroying tissues
what are exotoxins?
priduced inside mostly gram-positive bacteria as part of their growth and metabolism. they are then released into the surrounding medium.
what are endotoxins?
part of the outer portion of the cell wall of gram-negative bacteria. they are liberated when the bacteria die and the cell wall breaks apart
what is mycology?
the study of fungi
what are the two types of fungi?
macroscopic and microscopic
what type of fungi is included in microbiology?
microscopic
what are macroscopic fungi?
mushrooms and truffels
what are microscopic fungi?
yeasts and moulds
what type of metabolism does fungi have?
lika animals, incapable of producing food
chemoheterotrophs which is the use of organic chemical substances as sources of energy
saprophytes which is the use of obtaining nutrients from dead organic metals
what are the oxygen requirments of fungi?
most fungi are obligate anaerobes
some yeasts, however, are facultatively anaerobic and can obtain energy from fermentation
what are the chemical and physical requirments for fungal growth?
grow better at pH of 5
grow in high sugar ad salt concentration; resistant to osmotic pressure
can grow in low moisture content
can metabolize complex carbohydrates
what are the characteristics of yeasts?
monocellular
asexual reproduction (mainly budding)
form white, smooth, round uniform colonies
what are the characteristics of moulds?
pluricellular
asexual or sexual reproduction
fuzzy colonies with a variety of colours
what are the main differences in cellular composistion of fungi and bacteria?
fungi;
eukaryotic
sterol present in cell membrane
glucan and chitin (no peptidoglycan ) present in cell wall
nucleus present
organelles present
bigger
what are the differences between fungal and mammilian cells?
prencece of a cell wall
plasma membrane posseses different sterols
presence of vacuoles
what is the composition of the cell wall in fungi?
chitin layer, a long polymer of N-acetylglucosamine (NAG)
glucans network
mannoproteins on the external side
what is the composition of plasma membrane in fungi?
ergosterol is peculiar to fungal cells
what in the cell wall of fungi is the target for selective antifungal drugs?
echinocandin which i the target for the synthesis of glucans
what in the plasma membrane of fungi is the target for selective antifungal drugs?
polyemes which targets ergosterol and causes pores in the cell membrane
azoles and allylamines which prevent the synthesis of ergosterol
what is the importance of fungi for humans?
degrading organic materials
making alcoholic beverages
food preperation
commercial production of some organic acids
manufacturing of drugs and antibiotics
commensal microbes of normal microbiota
what are the harmful effects of fungi for humans?
food spoilage
contamination of pharmacetical preperations
causing diseases–> mycoses
how are mycoses spread?
spread generally from the environment to people (by spores)
what are the mycoses entry sutes?
skin-direct contact, cuts, splinters
lungs- inhaling spores
what are the mycoses virulence factors?
mycotoxins
enzymes
what are the types of fungal infections?
superficial
cutaneous
subcutaneous
systemic
opportunistic
where is the location of superficial fungal infections?
outer skin layer or on hair shafts caused mostly by yeasts
where is the locatio of cutaneous fungal infections?
affects keratin-containing tissues
where is the location of subcutaneous fungal infections?
chronic infection of subdermal tissues may require surgical intervention
ere is the location of systemic fungal infections?
infection deep within body, affects many tissues and organs
what is the opportunistic fungal infections?
caused by normal microbiota or fungi that are not ususally pathogenic
what are the patients at risk of mycoses fungal infections?
im paired immune system
solid organ transplantation
chemotherapy for malignant cancer
indwelling catheters
surgery and long-term use of corticosteroids
what is the most clinically relevant yeast?
genus candida
normally lives in the oral cavity, GI and genital tracts
most common cause of fungal opportunistic infections
what areas can candida (candidasis) affect?
oral candidiasis/thrush
vaginal candidiasis/thrush
invasisve candidiasis/thrush
what is hyphae?
multicellular organisms consisting of threadlike tubular structures
form together to produce a mat-like structure called a mycelium (fuzzy appearance)
what are the two types of mould colony?
vegetative myecelium (elongates to obtain nutrients and anchor the mould on the agar)
aerial myecelium (grow on top and have reproduction function, producing spores)
hoe does moulds reproduce?
can be sexual or asexual
what are genus aspergillosis?
ubiquitos moulds found in soil, on plants
what are some of the types of aspergillosis?
pulmonary aspergillosis (the most common. interstitial pneumonitis or localised ball-shaped infiltrates)
invasive aspergillus (infection can spread from lung to heart, brain, kidneys
what are the general characteristics of a virus?
not cells- acelular infectious particles
do not grow or undergo division outside a cell
obligate intracellular parasites- requirs a host for replication
carry genetic material either DNA or RNA
are produced by replication from the asembly of pre-formed viral components
what is the composition of a virus?
virion- complete, fully developed viral particle composed of
nuclec acid
capsid
envelope
what is the viral envelope?
external layer of a virion
envelope is a lipid bilayer derived from ost cell
envelope acquired by buddin of capsid when viruses leaves the cell
what are the viral envelope glycoproteins?
- Transmembrane glycoproteins (encoded by the viral
genome) that protrudes outside the envelope
Synthesised through the secretory pathway – destined
to the plasma membrane - Involved in binding specific protein receptors on the external
surface of the host’s cell (viral absorption, the first step) - Also, sometimes involved in viral-cell fusion
- In some viruses, those external proteins have other names
e.g. hemagglutinin and neuraminidase in influenza viruses
what is the viral capsid?
Large and protective shell that surrounds/protects viral nucleic acid –
Also called nucleocapsid
Composed of many capsomers (identical subunits - like the pieces of a puzzle)
Each one has ‘identical’ and reversible bonding contacts with its neighbours
what are the types of capsid shape?
helical
polyhedral
complex
what are the viral genomes in the nucleic acids of a virion?
- Viruses contain either DNA or RNA
- Can be double-stranded (ds) or single-stranded (ss), linear or circular
- Viral genomes possess only the genes to encode proteins involved in:
The structure of the virion (capside protein, envelope glycoproteins)
Invading the host cells and hijacking/regulating its metabolic activity to
produce more viral proteins and quench the production of cellular proteins
Enzymes to reproduce/multiply their genomes (e.g. DNA/RNA polymerases)
what are the genric steps in viral replication cycle?
1)attachment- a generic virus becomes attached to a target epithelial cell
2) penetration- the cell engulfs the virus by endocytosis
3) uncoating -viral contents are released
4) biosynthesis- viral RNA enters the nucleus, where it is replicated by the viral RNA polymerase
5) protein synthesis, protein maturation and virion assembly
6) release- new viral particles are made nd released into the extracellular fluid. the cell, which is not killed in the process, continuous to make new virus
what are prions?
proteinaceous infectious particles -misfolded proteins
what are asymptomatic infections?
virus encounter with no consequence
inapparent or asymptomatic
Signs: Evidence of disease that can be observed by others
Symptoms: Apparent only to the patient
what are acute infections?
Viruses can cause acute infections
display short incubation periods upon virus entry
into the host.
Rapid onset of disease
Brief period of sympthoms
Quick resolution (elimination of virus by the
immune system)
what is a latent infection?
Latent virus remains in asymptomatic
host cell for long periods
* No symptoms or viruses are detectable/active
* May reactivate due to changes in immunity
* Cold sores (e.g. herpes simplex virus, HSV-1),
shingles (varicella zoster virus, VZV)
what is a persistent/ chronic infection?
A persistent viral infection occurs
gradually over a long period;
* Hepatitis B virus (HBV )infection, where the
virus continue to replicate over time a low level
* Not all HBV infections become chronic
what are viruse k nown to cause cancer called?
oncoviruses
what can oncoviruses do?
Encode proteins that act as oncogenes themselves
Activate cellular proto-oncogenes (normal) to oncogenes
(hyperactive) - different ways
Inactivate tumour suppressor genes
* Cell cycles are no longer regulated at checkpoints (in a normal
conditions, If conditions are not right, cell cycle pauses at checkpoints)
Unregulated cell proliferation – cell cycle/division is always on
Genetic/chromosome instability - mutations accumulation in many genes
how are viruses isolated and cultivated?
- Cell are prepared to grow in plates similar to Petri dishes
and sample containing viruses are added to allow virus to
attach to the cells and then removed - Cell are then covered with Agar or other reagents to block
the diffusion of viruses. Virions progenies produced by a
single cell could only infect surrounding cells. - As result, there will be localised area of cell destroyed (viral
plaques) and detected by using a dye to stain just the viable
cell. The dead cells of the plaque do not retain the dye. - Each plaque corresponds to an area of cells infected and
dead by single virus; expressed as plaque-forming units
(PFU)
what are vaccinations used for?
Vaccines are predominantly used to prevent viral infections/severe diseases
* Establish a protection in immunized people which will protect them from:
a possible infection and/or subsequent illness when they come into contact with
the respective pathogens
Many technologies available to develop vaccines (e.g. providing dead/attenuated
viruses or proteins or mRNA to trigger a specific immune response)
Some viral diseases, often deadly have been eradicated (e.g. Smallpox) or almost
eradicated (e.g. Poliomyelitis caused by poliovirus)
what are the common characteristics of the HIV virus?
HIV belongs to the Retroviridae family, classified into
two subtypes: HIV-1 and HIV-2. HIV-1 is more virulent
and more infective.
Viruses that insert a copy of its RNA genome into the host
cell’s genome (lifespan chronic infection).
HIV virion (viral particle)
Knipe, et al. 2001. Fields Virology.
HIV causes acquired immunodeficiency syndrome (AIDS),
a condition in which progressive failure of the immune
system (decreasing CD4+ T-lymphocyte count) allows life-
threatening opportunistic infections (e.g. Criptococcus) and
cancers (oncovirus) to thrive.
what are the progression steps in the HIV?
acute HIV: flu-like symptoms that occur days to weeks after contracting HIV
chronic HIV: the latent and asymptomatic stage that can last several years
AIDS: occurs when CD4 cell count falls below 200 cell/mm3. tjis makes people vulnerable to opportunistic infections and AIDS-defining conditions
what is the principle for combination therapy?
Combining different antiviral drugs with distinct mechanisms of action having
a proved synergistic activity against HIV
what are the goals of HIV combination therapy (HAART)?
Reduce plasma viral RNA to an undetectable level
Prevent or reduce drug resistance
Reduce morbidity and mortality
Prevent HIV transmission
undetectable= untransmittable
what is a parasite?
livig eukaryote orgabism, which takes its nourishment and other needs from a host.
depends on the host for nutrition
what is the difference between endoparasites and ectoparasites?
endoparasites are inside the body -permanently
ectoparasites are on the outer surface of the hosts body- temporarly or permanently
what are the two types of endoparasites?
protozoa
helminths
what are the characteristics of protozoas?
monocellular
mostly asexual reproduction and sexual reproduction
some are non-motile, those motile use either flagella or cilia
Ranging in size - 2-100 μM
* Require high moisture environments
* Diverse oxygen requirements
* All protozoa are chemoheterotrophs
preformed organic substances
Similar requirements of the mammalian cells
* Establish parasitic relationships with many hosts
what are the characteristics of helminths?
pluricellular, parasitic worms
sexual reproduction
move through muscular contractions
what are the two morpholocigal forms of protozoa?
trophozoite
cyst
what are trophozoite protozoa?
motile, vegetative (active ) form
actively feed and multiply
pathogenic form
what are cyst protozoa?
External, non-
parasitic form
Possess a protective
membrane or
thickened wall
(survival outside the
host)
Means of transfer
between hosts
how is intestinal protozoa transmitted?
contamination of water, food, or hands with infective cysts
cysts ingested
giardia mature and multiply in the gut
infective cysts passed in stool
what are the different classifications for protozoa mobility?
amoebae- amoeboid movement (temporary extensions of the plasma membrane)
flagellates- use flagella
ciliates- use cilia
sporozoa- non-motile, spore-producing protozoa
what are the steps in the transmission of blood borne protozoa- leishmania?
1) sandfly takes a blood meal
2) promastigotes are phagocytized by macrophages or other types of monocellular phagocytic cells
3) promastigotes transform into amastigotes
4) amastigotes multiply in cells of various tissues and infect other cells
5) sandfly takes blood meal
6) ingestion of parasitized cell
7) anastigotes transforms in to promastigote stahe in the gut
8) divide in the gut and migrate to proboscis
what types of dideases does leishmaniasis produce?
cutaneous leishmaniasis- affects the skin
mucosal leishmaniasis- affects the mucous membranes of the nose and mouth, causng sors and destroying tissues
visceral leishmaniais- affects the internal organs, particularly the bone marrow, lymph nodes, liver and spleen
what are ciliates?
complex protozoa that move by cilia distributed in rows or patches
unusually, they have two different types of nuclei
what are sporozoa?
do not have any locomotory extensions
complex life cycles (alternating sexual and asexual reproduction, usually have more than one host)
intracelluar parasites
what is plasmodium?
agent responsible for malaria
transmission- spread to humans by the bite of female mosquitoes of the genus Anopheles
blood transfusion
mother to fetus
what is the prevention of malaria?
One vaccine (RTS,S) available showing modest efficacy, preventing about 30%
of severe malaria cases
Prevention
* Drugs to prevent malaria (prophylaxis, reducing the risk of malaria of 90%)
before travel into an endemic area until 4 weeks after leaving the area
Atovaquone plus proguanil – started 1-2 days before the travel
Doxycycline (Vibramycin-D) – started 1-2 days before the travel
Mefloquine (Lariam) – started 2-3 week before the travel
Chloroquine and proguanil – started 1 week before the travel
* Personal protection against bites (Insect repellents, covering clothes, nets)
50% Diethyltoluamide (DEET),
* Environmental mosquito control (
what is the treatment of malaria?
Artemether with lumefantrine is the drug of choice
* Artenimol with piperaquine phosphate – 2nd choice
* Quinine or atovaquone with proguanil hydrochloride - Alternatives
what are antiprotozoal drugs?
- Protozoal diseases are no
longer confined to specific
geographic locales - Unicellular eukaryotes, less
easily treated than bacterial
infections - The mechanism of drug action
for most antiprotozoan drugs is
not completely elucidated - Many of the antiprotozoal drugs
cause serious toxic effects in
the host (e.g. Mefloquine) - Most antiprotozoal agents have
not proven to be safe for
pregnant patients.
what are the principles of microorganisms identification?
- Microscopic examination to identify the morphology of microbes in specimens,
- Study of the growth and biochemical characteristics of isolated
microorganisms (pure cultures for bacteria and fungal cells, virus cultivation,
specific biochemical tests based on the properties of the microbe) - Immunologic tests that detect antibodies or microbial antigens/proteins (e.g. ELISA
tests, Later Flow Tests)
To detect the presence of a microbial protein/antigen in a sample using
antibodies directed against the protein (highly specific) linked to enzymes, or
viceversa - Molecular methods (detecting the specific genome of a certain microorganism)
Polymerase Chain Reaction (PCR) based techniques allow amplification of a
known gene of interest (based on unique sequence of nucleotide)
nucleic acid sequencing
