Microbiology and parasitology Flashcards
Name 4 genera of Enterbacteriaceae
Escherichia, Salmonella, Shigella and Enterobacter.
Give the gram stain for A) Actinobacillus, B)Ureoplasma, C) Chlostridium, D) Campylobacter and E) Mycobacteria
A) Negative B) Mycoplasma (no stain) C) Positive D) Negative E) Acid Fast
What morphology is staphylococcus?
‘Bunch of grapes’
Where would you find streptococcus as a commensal?
Mucous membranes
What type of bacteria causes bovine TB? What’s its gram stain?
Mycobacterium Bovis, Acid fast.
Name 2 bacteria genera that form endospores
Chlostridium and bacillus
What is the difference between acid fast and gram positive?
Acid fast contain mycolic acid which gives a waxy appearance.
How many membranes does gram positive have?
1
What family of bacteria do XLD and MacConkey agar select?
Enterobacteriaceae
What does MacConkey agar distinguish between and how does it indicate the presence of certain bacteria?
Distinguishes between lactose positive and lactose negative enterobacteriaceae. Contains lactose and neutral red (a pH indicator), when lactose is fermented the pH changes causing the indicator to turn from red to pink.
What does XLD stand for? How does it differentiate between shigella and salmonella?
Xylose-lyseine-deoxycholate.
Indicator based on a pH change, if xylose is fermented it goes from pink to yellow (shigella cannot do this) Salmonella will then ferment lyseine, thus returning the colour to pink, but they’re not indistinguishable from Shigella because they will then metabolise thiosulfate to produce H2S, which appears as a black dot.
What is A) Alpha, B) Beta and C) Gamma haemolysis? With reference to blood agar. Give the colour of the blood agar for each.
A) Incomplete haemolysis (green/yellow)
B) Complete haemolysis (Clear)
C) Absence of any haemolysis (Red - unchanged)
Positive result for catalase test
O2 gas produced (cloudy)
Positive result for oxidase test
Turns blue
What does typing of bacteria achieve?
Differentiates between bacteria of different linneages (but of the same species)
Briefly outline phage typing of bacteria.
Panel of viruses (bacteriaphages) are used, each of which binds to a different bacterial receptor. A pattern of susceptibility is produced by seeing which virus panels show a positive result. This establishes a phage type (PT)
What is an LPS? And where are they found?
A lipopolysaccharide. Composed of a lipid, and a polysaccharide which is composed of O-antigen. They are found on the outer membrane of gram negative bacteria.
Briefly outline serotyping of bacteria
Where a panel of antibodies attach to specific bacterial receptors (usually O-antigens in gram neg), giving a pattern and establishing a serotype. Small changes in O-antigen lead to changes in binding, so give a different pattern of susceptibility.
In the serotypes O157, K12 and H7, what do O, K and H stand for?
O - LPS (O-antigen)
K - Capsule
H - Flagella
Briefly outline molecular typing - just kinda say what it does and why this works….
As DNA replicates mutations occur, over time these build up in populations that have grown independently. Molecular typing then identifies the mutations and can group bacteria based on this.
How would you identify specific traits that a colony of bacteria has?
PCR is used to amplify the gene. If it works, then you have that trait!
What happens if the immune system gives too much of a response?
toxic shock syndrome
What is biofilm/plaque?
Colony of bacteria adhered to a surface, e.g. teeth.
What are the main two structures bacteria use in adhesion?
Fimbrae/pili (adhere at a distance) and adhesive macromolecules imbedded in the membrane(Adhere nearby)
Which of the two adhesive structures is more common in gram positive bacteria?
Fimbrae/pili
Give 2 ways in which bacteria resist the complement system
Develop long LPS chains to hinder binding.
Incorporate sialic acid on capsule, inhibiting complement binding.
Give 2 ways in which bacteria avoid phagocytosis
Capsules contain anti-adhesive molecules
Produce FC-binding proteins which block their own receptors
Name 3 ways in which bacteria exploit host cell cytoskeletons
To invade cells (Trigger and zipper)
For extracellular attachment (E.Coli pedestal)
For movement in and between cells (Listeria actin tail)
What are type III secretion systems? (TTSS)
syringe-like structure embedded in both membranes of some gram negative bacteria. They often produce toxins and inject them directly into the host cell
Briefly outline the trigger mechanism of invasion
Effector proteins injected into cell via TTSS, these interfere with the cytoskeleton of the host cell and stimulate actin polymerisation. This causes the cell to wrap around the pathogen and phagocytose it.
Briefly outline the zipper mechanism of invasion
Bacteria bind to host membrane receptors, host tries to form a cell junction and spreads over pathogen, phagocytosing it.
how do bacteria (e.g. shigella, salmonella) escape lysosomes?
Use TTSS to secrete haemolysins out into the cytoplasm. This breaks down the endosomal lining. It is quickly broken down so that it doesn’t damage the host cell membrane.
How do bacteria live extracellularly? (e.g. pathogenic E.Coli)
It injects Tir, an adhesin, into the cell using a TTSS.Tir binds to intimin on bacterial membrane interfering with the host cell’s cytoskeleton whichleads to the formation of a pedestal on which the bacterium sits.
How does listeria exploit the host cell cytoskeleton to move in and between cells?
It uses and assembly of actin at one end, propelling it through the cytosol. Depolymerisation occurs at the end so it appears as a tail. It can have enough force to push it through one cell into an adjacent one!
What is meant by the term endogenous pathogen?
One that is already present on the animal as a commensal (but something changed to make it cause disease)
What are the two terms which describe how fungi obtain their nutrition>?
Saphrophytes - feed on dead matter
Dermatophytes - feed on skin
What are the two forms of fungi and what is their basic defining feature?
Yeasts - oval/spherical
Moulds - hyphal forms (filaments)
What is meant by the term dimorphic fungi?
Can grow as yeasts or moulds depending on temperature.
What are hyphae?
Tubular fungal cells that grow outwards to form mycelium
What is mycelium?
Mass of branching thread-like hyphae
What are the two types of hyphae?
Coencytic - no septa between hyphal cells
Septate - septa present between hyphal cells
What are septa?
Ingrowths of the chitin cell wall between hyphal cells in septate hyphae. They contain lots of gap junctions to allow movement of ions, etc between cells.
What are conidia?
A type of asexual spore released by fungi
What are conidia produced by>
Phialoconidia - flower like structures formed off hyphae
What is the other type of asexual spore (not conidia) and what structure produces them?
Sporangiospores, released by sporangiophores (spone like strucutures)
What are macroconidia?
Multicellular conidia produced by dermatophytes.
How do yeasts reproduce?
Asexually through budding.
How do aspergillus sp. get their nutrients, what type of spores do they produce and what type of hyphae do they have?
Saphrophytes (dead matter), produce conidia from phialoconidia, and have septate hyphae.
What area of the canine body does aspergillus affect?
Nasal tract and paranasal sinuses.
What is a virion?
A mature virus particle
What is sense in terms of virus classification?
Used to compare the polarity of nucleic acids, e.g. positive sense is 5’ - 3’
What are retroviruses?
Single stranded RNA viruses (ssRNA) which produce reverse transcriptase to convert their ssRNA into double stranded DNA.
Outline immunohistochemistry to diagnose viruses
Antibodies used to label viruses in tissue. Can either be fluorescent or enzyme linked - either way they make the tissue change colour where infected.
How to isolate a live virus culture? 4 ways.
They are obligate intracellular parasites so can either use cell culture, fertile egg infection, experimental animals or organ culture.
Briefly describe 2 ways in which an enveloped virus can enter the cell.
Direct fusion with host membrane
Receptor-mediated endocytosis - virus then has 2 membranes… see next card
In receptor mediated endocytosis, how does the enveloped virus remove itself from the membranes?
Acidification of the endosome is a normal cell process, when this occurs it causes a change in the viral envelope proteins, these then insert on the endosomal membrane and merge the two membranes together, releasing the capsid in the process.
Describe how non-enveloped viruses enter the host cell through pore formation
Virus binds to receptor, and is endocytosed. The virus then injects viral proteins into the cytosol from a pore it has made in the endosome. This is how it releases its genome into the cell.
Outline antigen shift
Where 2 viral strains of the same species infect the same host, so viral genes get mixed up and this forms a new strain.
What does PAMP stand for and what is it?
Pathogen-associated molecular pattern.
They are specific components on pathogens that are recognised as danger signals.
What PAMPs are present on A) Gram positive and B) Gram negative bacteria?
A) Peptidoglycan
B) LPS (O-antigen)
What are PRRs?
Pattern recognition receptors - they are host cell receptors that recognise PAMPs.
What are TLRs?
A type of PRR called toll-like receptors which span the whole membrane.
What is meant by the term indirect parasite?
When an intermediate host is required to complete the life cycle
What is a definitive host?
The host in which parasite sexual reproduction occurs
Define permissive host
Host not usually fvoured by parasite but will be infected in the abscence of the right host - can still complete life cycle
Non permissive host
Parasite will infect this host in abscence of normal host, but cannot complete life cycle
Paratenic host
host used for transport
What are the two types of vector in parasite transmission?
Biological - needed as part of life cycle
Mechanical - just used for transport
