Pathogens Flashcards
Why don’t we usually see bacteria on micrographs?
they stain poorly with H and E, the tissue preparation deliberately removes them or insufficient magnification
What is a microbiome?
The collection of microbes usually present on a human. This will be dependent on the health of the human in question.
What can we detect with Acid-Fast Stain?
The bacterial causes of tuberculosis and leprosy.
How does Gram stain work and what are the results?
Positively charged crystal violet binds to negatively charged cell components. We attempt to extract the complex and then add red dye.
Red = gram negative
Purple = gram positive
Why do some bacteria stain positive with Gram stain?
They have thicker peptidoglycan cell walls which prevent the extraction of the complexes of Gram stain.
Name 3 ways that bacteria can grow
broth turbidity, colonies and biofilms
What are the requirements for bacterial growth?
specific energy source, specific building blocks and specific atmosphere
Name some Gram positive bacteria
staphylococci, streptococci and clostridium
Name some Gram negative bacteria
Neisseria, Salmonella, Helicobacter, Pseudomonas, Legionella
What are the differences between prokaryotes and eukaryotes?
P: 1 chromosome, no introns, 70S ribosomes, cell walls, coupled transcription and translation
E: many chromosomes, introns, 80S ribosomes, no cell walls, compartmentalised transcription and translation
Where do most infections take place?
The epithelial tissue
Define infection
The establishment of an organism on or in a host associated with its multiplication and damage to or dysfunction of the host specifically related to the organism or its products.
How do viruses affect histology?
viral inclusion bodies (Negri bodies) and cytopathic effects
What kind of nucleic acids do viruses contain?
RNA or DNA (But not both)
Are enveloped or naked viruses harder to destroy?
Naked viruses
Which processes do the viruses require hosts for?
energy generation, protein synthesis and nucleic acid synthesis
What does it mean if the virus has +ssRNA?
The genomic RNA can serve as mRNA and be directly translated into protein.
What does it mean if a virus has -ssRNA?
The genomic RNA cannot serve as mRNA and therefore cannot be directly translated into a protein.
This is because the sequence is the complementary sequence to the one we need for translation.
If the virus contains RNA, what enzyme will be required for DNA synthesis?
Reverse transcriptase
What is a nucleocapsid?
A protein coat which encloses and protects genomic material.
May be involved in attachment to host cells.
What is the envelope made from?
A piece of host cytoplasmic membrane
What is the capsid composed of?
Individual subunits called capsomers.
What are the 2 basic capsid structures?
Icosahedral
Helical
What are bacteriophages?
Complex viruses that are involved in transfer of drug resistance. They can inject DNA through cell walls.
Which receptor does HIV bind to?
The CD4 receptor on T lymphocytes
Define host range
The spectrum of host cells that the virus can successfully infect and replicate in.
How do we classify viruses?
Baltimore Scheme
Based on the relationship between the viral genome and the mRNA used for translation.
Name some enveloped DNA viruses
Hepatitis B
Herpes
Small pox
Name some non-enveloped DNA viruses
Papilloma viruses (warts and cervical cancer)
Name some enveloped RNA viruses
Rubella HIV Influenza Measles Mumps
Name some non-enveloped RNA viruses
Polio
Hepatitis A
Colds
Name some cytopathic effects
syncytic formation - giant multinucleated cells formed by fusion of plasma membranes
And chromosomal damage
What is damage in infections often due to?
Ineffective host responses rather than direct toxicity of the microbe
What is a latent infection?
The organism is not eliminated from the body but there are no symptoms. Many things may lead to its reactivation.
How are new virus particles formed?
They are assembled within the host cells and then released by budding off or during cell lysis.
How can viruses spread in the body?
Via nerves and the blood
