Nature and Properties of Micro-organisms Flashcards
List the types of microbe in order of smallest to largest
Prions Viruses Prokaryotes --> bacteria Eukaryotes Fungi Parasites
What as the causative agent of Creutzfeldt-Jakob disease? What is CJD?
Prions
A disastrous spongiform encephalopathy
What are prions and how do they cause disease?
a mutant protein with no DNA or RNA
The mutant protein induces misfiling of normal host proteins in an exponential chain reaction
In humans the normal PrPc (prion protein, cellular) is converted into PrPsc (sc for scrapie) which is found in neural tissue and tonsils
The proteins fold to form amyloid fibres which aggregate and lay down deposits in the brain causing degeneration of function
How fatal is CJD? Is there treatment? What are the causes? How is it transmitted? Why are prions extremely difficult to remove or inactivate?
fatal
no treatment
sporadic (mutation), familial, transmission
Transmission = oral, operative, blood
Prions are resistant to disinfectants and heat treatment so sterilisation is an issue
What does BSE stand for?
What is its colloquial name?
How does it cause vCJD?
Bovine spongiform encephalopathy.
Outbreak of BSE in cows in 1980’s.
The bovine prion is sufficient;y sumilar to the human prion to cause the disease hence acquisition via infection
vCJD are cases caused by ingestion of mutant prions from BSE infected cows
Describe the generic structure of viruses
They are ubiquitous - found everywhere
They are not a cell, they are a shell of protein surrounding nucleic acid, usually DNA or RNA
Use host cell machinery to replicate
Give an example of a DNA virus and an RNA virus
DNA virus = herpes simplex virus
RNA virus = influenza virus
What is the baltimore scheme?
Viruses grouped on the basis of their genome and how it is replicated
Useful as can predict behaviour of members of the same group
Seven classes of virus
List the stages in a simple viral life cycle x6
Attachment to host cell
Entry of host cell
Loss of envelope/release of viral nucleic acid
Replication of genome and protein production
Assembly of new virions
Release from cell - escape to infect new host cells
What two stages of the viral life cycle are targeted by antivirals?
initial attachment
intracellular replication process - e.g. retroviruses such as HIV
List some viral effects on host cells
- vary from innocuous to lethal
- degeneration
- cell lysis
- cell fusion, syncytia formation
- cell proliferation
- transformaton e.g. malignancy
- latent infection - no sign of infection until reactivation
What is CMV hepatitis?
What is the diagnostic tool?
Cytomegalovirus infection in liver
Owl eye effect inclusion body
What is VZV?
Varcella Zoster Virus
Chickenpox and shingles
Re-activation of latent infection
Suppression of cell mediated immunity
Facts about Ebola
- the virus
- the mechanism
- the symptoms
- treatment?
Family of related filoviruses
Hemorrhagic fever
ssRNA genome
attacks endothelial cells, mononuclear phagocytes and hepatocytes
Immune response results in pathology e.g fatigue, fever, headaches, pain, vomiting and diarrhoea
Supportive treatment, novel protective vaccine appears successful
Infection control key to ending the outbreak
Facts about Zika
- what is it proposed to cause?
- transmission
- diagnosis
- treatment
- microcephaly in neonates, Guillain-Barre syndrome
- infection via infected Aedes mosquito bite and body fluids
Diagnosis = history and blood test for presence of virus (cross-reactivity with other viruses of the same group e.g. yellow or dengue fever, west nile viruses)
Treatment = pain releif, rest and rehydration
Describe what is meant by the following?
- commensals
- opportunistic pathogens
- obligate pathogens
- most microbes are never pathogenic to humans, we live in harmony with them
- many microbes can be pathogenic if they end up where they shouldn’t e.g. MRSA
- very few microbes are always pathogenic e.g. salmonella and TB
What is the general structure of prokaryotes?
- lack a nucleus, mitochondria, ER, golgo etc
- usually have a cell wall (peptidoglycan)
- can have protruding appendages (flagella, fimbriae)
How are bacteria classified?
Based on nucleic acid sequences
There is one large division which divides most bacteria into one of two groups - gram negative (pink) or gram positive (purple)
Describe the different in cell structure between gram negative and positive bacteria and how this affects staining
Gram negative - PINK - double membrane, thin peptidoglycan - purple is washed out as it can get in and out of membrane Gram positive - PURPLE - single membrane, thick peptidoglycan - purple remains due to thick pg
How do bacteria cause disease?
Varies enormously! Some invade cells Occupy very different niches Disease is a combination of: - bacterial activity - toxins, direct tissue damage - host activity - immune response
What are the bacterial products that cause disease?
Some bacterial products are designed to damage the host = TOXINS
Some are immunogenic and result in damage indirectly = LPS, FLAGELLA
What is LPS?
Lipopolysaccharide (endotoxin)
Firmly bound to cell and only released upon lysis
Only Lipid A is toxic - major immune response
Polysaccharide is a major surface antigen - O antigen
Antigenic specificity conferred by the terminal repeat units, and many types possible e.g. Salmonella
What are flagella?
What is their function?
Molecular motors used to swim
Important in pathogenesis - burrow into mucus membrane
Involved in motility and impart spinning movement and usually requires proton motive force
Chemotaxis: flagella move bacteria towards or away from chemical attractant/repellent e.g. Vibrio cholerae
Often immunogenic and induce inflammation
What are pili (fimbrae)
Shorter and finer than flagella
Ordinary pili ‘colonisation antigens’:
- protein, attachment to host cells e.g. UTI
- can be involved in host cell invasion
Sex pili role in conjugation (transfer DNA plasmid)
What part of the bacteria is extracellular polysaccharide?
What is its purpose?
Capsule
condensed, well defined layer closely surrounding the cell contributes to invasiveness of pathogenic bacteria by reducing opsonisation and protection from phagocytosis
Define exotoxins
What are toxins used for?
Give two examples
proteins secreted by bacteria Used to destroy host cells, release cell contents or allow invasion e.g. C.tetani - active immunity: toxoid - passive immunity: antitoxin eg. C.botulinum - food poisoning - produces lethal neurotoxin - most potent poison known to man - used in botox!
For each of the following species, note the disease it causes and if its gram negative/positive
- E.coli
- Staphylococci
- Tuberculosis
- Pseudomonas
- S. pneumoniae
- Campylobacter
1. Bacteraemia, UTI, GI NEGATIVE, often part of flora 2. Wound infection, bacteraemia POSITIVE, often part of flora, MRSA 3. Mainly lung, can be multi system NEITHER, 1/3 of the world carry it 4. Varied disease NEGATIVE, environmental 5. RTI POSITIVE, aerosol 6. GI NEGATIVE, number one cause of food poisoning
What are the characteristics of fungi?
Can be single or multicellular
Eukaryotic so similar in machinery to human cells (hard to treat as similar to us)
Have a cell wall containing chitin
May be as many as 1.5 million species but very few studies
Include yeasts, moulds and mushrooms
What is the most common fungal infection?
Candida albicans –> oral thrush
Which fungal infection occurs in people with underlying illnesses such as TB or COPD?
aspergillus
What is the structure of fungi?
Can be single cells but most grow as hyphae - cylindrical tubes which interconnect to form mycelium
The mycelium can be very large
Can also produce variety of fruiting bodies and spores when reproducing
Which microbe describes each of the following?
- rare, infectious proteins cause CJD
- many, parasitic, need host machinery
- ubiquitous, produce components that cause damage or influence immunity
- eukaryotic, cause serious disease in immunocompromised patients
prions
viruses
bacteria
fungi
