Nature and Properties of Microorganisms Flashcards
Define prion.
A pathogenic protein that disrupts protein folding in an exponential chain reaction.
Give an example of a prion.
What disease is caused by this prion?
- The normal PrPc protein (found in neural tissue and tonsils) can be converted into PrPsc, a prion.
- PrPsc causes protein folding to form amyloid fibres, which aggregate and lay down deposits, causing Creutzfeldt-Jakob disease (CJD).
- This is a form of spongiform encephalopathy.
List 3 methods by which Creutzfeldt-Jakob disease can be transmitted.
1 - Sporadic (mutation).
2 - Familial.
3 - Oral and blood transmission (for particular variants of CJD only).
Why are prions difficult to remove or inactivate?
Because they are resistant to disinfectant and heat treatment.
What causes mad cow disease?
A prion similar to the human prion causing Creutzfeldt-Jakob disease.
Give an example of a DNA virus.
Herpes simplex virus.
Give an example of an RNA virus.
Influenza.
What is the Baltimore scheme?
Why is it useful?
- A system for categorising viruses on the basis of their genome and how it is replicated.
- It is useful as it can predict the behaviour of members of the same group.
What is a tegument?
A cluster of proteins that lines the space between the envelope and nucleocapsid of all herpesviruses.
List 2 important proteins that are expressed on the surface of the influenza virus.
1 - Neuraminidase.
2 - Haemagglutinin.
What is the function of neuraminidase?
To enable the virus to be released from the host cell by cleaving glycoproteins.
What is the function of haemagglutinin?
To facilitate entry of the virus into host cells by fusing the membrane of the virus and the host cell.
List the stages of a generic viral life cycle.
1 - Attachment to host cell.
2 - Entry into host cell.
3 - Loss of envelope and release of viral nucleic acid.
4 - Replication of genome and protein production.
5 - Assembly of new virions.
6 - Release from cell.
What are the two major sites of antiviral drug action?
1 - Cell attachment.
2 - Intracellular replication.
What is the effect of cytomegalovirus on the host cell?
Causes morphological changes, resulting in lysis.
What is the effect of respiratory syncitial virus on the host cell?
Cell fusion, causing the formation of syncytia.
What is the effect of parvoviruses on the host cell?
Can induce malignancies.
Describe the morphological change that would arise with cytomegalovirus hepatitis.
Causes an ‘owl-eye effect’ inclusion body (an aggregate of proteins).
List 2 diseases that can be causes by varicella zoster virus.
1 - Chickenpox.
2 - Shingles.
List 2 viruses that cause latent infection.
1 - Herpes simplex virus.
2 - Varicella zoster virus.
To which family of viruses does ebola belong?
Filoviruses.
What type of genome does ebola have?
Single stranded RNA.
List the cells that are targeted by ebola.
1 - Endothelial cells.
2 - Mononuclear phagocytes.
3 - Hepatocytes.
Define ring vaccination.
A strategy to inhibit the spread of a disease by vaccinating only those who are most likely to be infected.
List 2 diseases caused by zika virus.
1 - Microcephaly (abnormally small head in neonates).
2 - Guillain-Barre syndrome.
How is zika virus transmitted?
1 - Via infected Aedes mosquito bites.
2 - Sexually transmitted.
How is zika virus treated?
Only by treating symptoms (mostly pain relief) rather than curative treatment.
What is the name of bacteria that are never pathogenic?
Commensal bacteria.
What is the name of bacteria that can be pathogenic, but are not always pathogenic?
Opportunistic bacteria.
What is the name of bacteria that are always pathogenic?
Obligate bacteria.
List 2 opportunistic bacteria.
1 - Pseudomonas.
2 - Most anaerobes, e.g. bacteroides fragilis.
List 3 characteristics of prokaryotes.
1 - Lack a nucleus.
2 - Usually have a peptidoglycan cell wall.
3 - Can have protruding appendages.
How do gram negative and gram positive bacteria stain in a gram stain test?
- Gram positive stain purple.
- Gram negative stain pink.
How is a gram stain test done?
1 - Application of crystal violet.
2 - Decolorization.
3 - Counterstaining, usually with safranin.
List 4 gram negative bacteria.
1 - E. coli.
2 - Klebsiella.
3 - Pseudomonas species.
4 - Campylobacter species.
List two gram positive bacteria.
1 - Staphylococcus species.
2 - Streptococcus species.
Why do gram positive bacteria retain crystal violet dye whereas gram negative bacteria do not?
- Gram positive cells have large cell walls lined exteriorly with peptidoglycan, which retains the dye.
- Gram negative bacteria have two thin cell membranes with a thin peptidoglycan layer between them in the periplasmic space. They are therefore unable to retain the dye.
What is lipoteichoic acid?
How does it cause pathogenic effects?
- A surface-associated adhesion molecule in gram positive bacteria that spans the width of the peptidoglycan.
- It is an immune irritant that causes septic shock.
How do endotoxins (lipopolysaccharides) cause pathogenic effects?
Which bacteria use endotoxins?
- Endotoxins are immunostimulators that cause sepsis.
- Gram negative bacteria use endotoxins.
What is an O antigen?
What structural component of the O antigen gives a bacteria antigenic specificity?
- Part of the lipopolysaccharide in the outer membrane of gram-negative bacteria.
- It consists of oligosaccharide repeating units.
- Antigenic specificity is conferred by the terminal repeat unit.
List 3 drugs that target peptidoglycan.
1 - Penicillins.
2 - Cephalosporins.
3 - Vancomycin.
What is the name of the major toxic lipopolysaccharide?
Lipid A.
Define chemotaxis.
The process by which flagella move bacteria towards or away from a chemical attractant / repellent.
What are fimbriae?
Pili.
List 2 functions of fimbriae.
1 - Attachment to host cells.
2 - Transfer of plasmid DNA.
Define opsonisation.
The molecular mechanism whereby a cell is modified (addition of opsonins) to have a stronger attraction to the cell surface receptors on phagocytes.
Define exotoxin.
Protein toxins secreted by bacteria.
What is a toxoid?
A chemically modified exotoxin that is no longer toxic, and can be used for vaccination.
Give an example of a passive immune defence against exotoxins.
Antitoxin.
What might cause cultures of Clostridium botulinum to form?
Poor canning.
How does Clostridium botulinum cause pathogenic effects?
By producing a neurotoxin which causes paralysis.
List 3 diseases caused by E. coli.
1 - Bacteraemia.
2 - UTIs.
3 - GI infections.
List 2 diseases caused by Staphylococcus species.
1 - Bacteraemia.
2 - Wound infections.
Which bacteria cause tuberculosis?
Mycobacterium tuberculosis.
Give an example of a species of bacteria that causes respiratory tract infections.
Streptococcus pneumoniae.
Which diseases does Campylobacter species cause?
GI infections.
Which disease does Clostridium difficile cause?
Hospital acquired diarrhoea.
Define sporulation.
What is the purpose of sporulation?
- The formation of nearly dormant forms of bacteria.
- In a limited number of bacteria, spores can preserve the genetic material of the bacteria when conditions are inhospitable.
Which species of bacteria causes gonorrhea?
Neisseria gonorrhoeae.
Which species of bacteria causes meningitis?
Neisseria meningitidis.
In which kingdom is chitin present in the cell wall?
Fungi.
What causes thrush (a vaginal yeast infection)?
Candida albicans (yeast).
What is aspergillosis?
In which conditions does it arise?
- A fungal infection caused by Aspergillus.
- Occurs in people with underlying illnesses, especially tuberculosis or COPD.
What is the most common structure in which fungi grow?
Hyphae - cylindrical tubes which interconnect to form a mycelium.
What type of disease is caused by Cryptococcus neoformans?
A respiratory yeast infection.
