Flashcards in Introduction to Microbiology Deck (82):
What is an akaryote?
A cell without a nucleus.
What is a prokaryote?
A single-celled organism that lacks a membrane-bound nucleus, mitochondria and other membrane-bound organelles.
What is a eukaryote?
An organism with DNA contained in chromosome in a distinct nucleus.
What proportion of the cells in the human body are not of human origin?
What are the cells in the human body that are not of human origin called?
Why are viruses not described as human commensal flora?
They don't have a cellular structure, and can only infect host cells.
What is the main type of bacteria found on teeth?
-commensal, but also causes disease
What is the main type of bacteria found on the tongue?
What is responsible for the initiation of 'dental caries', and what is the main risk factor?
-high sugar diets
Are most microorganisms beneficial or harmful?
Most are beneficial.
What is responsible for providing most of the vitamin K we require?
Who set out the criteria to decide whether bacteria cause disease?
Robert Koch (1834-1910).
What does Koch's postulates state? (4)
Causative organism must:
-be isolated from every individual
-be artificially cultivated
-lead to symptoms
-be recovered from individuals infected experimentally
What does Koch's postulate state for viruses?
-The gene should be present in a virulent strain, but not in a virulent strain
-Antibodies against the gene should protect subjects
What are the main problems of Koch's postulates?
-Difficult to isolate causative agents
-Impossible to culture some pathogens
-Ethics - animal models not sufficient
Give an example of a bacterium that is difficult to isolate.
Give an example of a bacterium that cannot be cultured.
-except in armadillos due to low body temperature
What different illnesses does Salmonella typhi cause in mice and humans?
MICE - gastroenteritis
HUMANS - typhoid fever
What different illnesses does Salmonella typhimurium cause in mice and humans?
MICE - fatal infection similar to typhoid fever
HUMANS - gastroenteritis
What type of parasites are viruses?
-rely upon other cells for replication
What is the general structure of a virus?
Nucleic acid core surrounded by a protein coat.
-some also have a lipid envelope
What can viruses infect?
Every class of organism.
What is the nucleic acid core in viruses made up of?
Either DNA or RNA.
What is unusual about retroviruses?
RNA genome >> cDNA copy upon infection of the host cell using reverse transcriptase.
What makes up the protein coat on viruses?
What area of the body does the syncytial virus infect?
What is the special class of virus that attacks bacteria?
What type of virus infects plants?
-naked infectious RNA molecules
What type of viral protein is thought to cause spongiform encephalopathies?
What type of organisms are fungi?
What is the cell wall of most fungi made up of?
-polymer of N-acetyl glucosamine
Where else is chitin found?
Exoskeleton of arthropods.
Why are fungi no longer thought to be plants?
Their cell walls are composed of chitin, not cellulose.
What are moulds?
-grow into filaments (HYPHAE) that form mats (MYCELIA). May be subdivided by cross walls (SEPTA)
What are the tiny filaments present in moulds called?
What are the mats that forms from hyphae in moulds called?
What type of fungus is common in bathrooms?
What type of fungus is common in stale bread?
What are yeasts?
What is the most common yeast in food production?
-bread, alcohol, etc
How do yeasts grow and multiply?
Budding daughter cells grow and multiply off mother cells.
Give 2 examples of superficial infections caused by moulds.
Give an example of an infection caused by yeast.
What are pseudomycelia?
A cellular association in bacteria and yeasts in which cells cling together in chains resembling small mycelia.
-e.g. candida albicans in thrush
What type of organisms are protista?
What are the 4 classes of protista?
What type of parasites are protista?
Intracellular and extracellular.
How do protista spread?
-Produce cysts >> outside body
Give examples of infections caused by protista.
What types of protista cause diarrhoea? (2)
-Cryptosporidium spp. (associated with AIDS)
What is Trichomonas vaginalis and what does it cause?
A protista, causes vaginal infections/discharge.
-can cause balanitis in males
What is Pneumocystis jiroveci?
-was thought to be a protista
-causes pneumonia in people with AIDS
What is the cell structure of bacteria?
-lack membrane-bound nucleus
What are the different shapes of bacteria?
How does gram staining differentiate between different types of bacteria?
Gram positive retain crystal violet dye when mixed with iodine >> PURPLE.
Gram negative are decolourised by iodine >> PINK.
What is the envelope of Gram positive bacteria made of?
-30-40 layers of peptidoglycan
-sugar and short peptides containing D-/L-amino acids
-polymers (e.g. teichoic acid)
What is the envelope of Gram negative bacteria made of?
-Very little peptidoglycan (1-2 layers)
-Contains complex 'outer membrane'
What does the outer membrane of gram negative bacteria contain?
-form surface antigen with lipid A >> endotoxin
What does the lipid A on gram negative bacteria cause?
Gram negative shock.
What makes bacteria mobile?
What are fimbriae?
Hair-like structures surrounding gram negative bacteria.
-aid adhesion onto surfaces
What are pili?
Tubes that join gram negative bacteria together during conjugation.
>>exchange genetic material
What structures are responsible for spreading antibiotic resistance between bacteria?
What is the function of the capsule surrounding some bacteria?
-even within phagocytes
What is the function of the slime produced by some bacteria?
Helps them to stick to surfaces.
What does the slime produced by Streptococcus mutans enable it to do?
Stick to the hard enamel on teeth.
-forms plaque and eventually dental caries
Where do coagulase-negative staphylococci live, and what sorts of infections do some strands cause?
On the skin, and some produce slime that enable them to stick to plastics.
-infections associated with implanted plastic medical devices
What are endospores?
Highly resistant structures produced by some bacteria that protect against heat and radiation.
How are infections spread?
-Innoculation (e.g. IV)
What infections are commonly spread by the faecal-oral route? (4)
What genus of protista causes malaria?
What is zoonosis?
The transmission of disease from animals to humans.
What is a fomite?
An inanimate object (e.g. pen) that is capable of transmitting infection.
What are virulence factors?
Molecules produced by pathogens that enable them to colonise a niche in the host/complete the cycle of infection.
What are intoxication illnesses?
Illnesses that can be caused from exposure to a toxin rather than a living organism.
-e.g. tetanus, botulism, ergotism
What is another name for tetanus?
-causes muscles to go into rigid spasm; face is affected first
What are the 2 types of toxins produced by bacteria?
Exotoxins and endotoxins.
What is the difference between endotoxins and exotoxins?
ENDOTOXINS - stored in bacterial cells and released when they disintegrate.
EXOTOXINS - secreted by bacterial cells.
What is the effect of some bacteria producing soluble antigens?
May combine with antibodies >> circulating immune complexes and become trapped in vessels.
What bacteria causes glomerulonephritis and rheumatic fever?
How do bacteria cause disease?
-Toxin production (endo-/exo-toxins)