Bacterial Properties Flashcards
What is the difference between Gram-negative and Gram-positive bacteria?
Gram-negative bacteria have a thin peptidoglycan layer with two membranes (cytoplasmic and outer membranes)
Gram-positive bacteria have a thick peptidoglycan layer, which retains the dye well. It only has one membrane
Give examples of some Gram-negative pathogenic bacteria and the diseases they cause.
E. coli – diarrhoea, dysentery, kidney failure Salmonella - food poisoning, typhoid Shigella – dysentery Neisseria – meningitis + gonorrhoea Vibrio cholerae - cholera
What feature is found only on Gram-negative cell walls?
Lipopolysaccharide
Give examples of some Gram-positive pathogenic bacteria and the diseases they cause.
Staphylococcus aureus – skin infections, endocarditis, bacteraemia, pneumonia
Streptococcus pneumoniae – pneumonia, meningitis, otitis media
Streptococcus pyogenes – tonsillitis, necrotising fasciitis, scarlet fever
Give examples of some Mycobaceria and the diseases they cause
Mycobacterium tuberculosis – TB
Mycobacterius leprae - leprosy
What is another way of classifying bacteria?
Intracellular and Extracellular pathogens
Give examples of some extracellular pathogens.
Staphylococcus
Streptococcus
Neisseria
Yersinia
What are the three methods by which bacteria survive in the host cell?
Escape
Preventing fusion with lysosome
Surviving in the phagolysosome
Give examples of bacteria that survive using each of the above methods.
Escape – Listeria, Shigella
Prevent fusion of lysosome – Salmonella, Mycobacteria, Chlamydia
Survive in phagolysosome - Coxiella
Motility and Invasion require which two multi-protein machines?
Flagella
Type III Secretion system
Describe the role of the type III secretion system.
A protein machine assembles which provides a channel through which virulence proteins can be injected into the host cell
The virulence proteins then stimulate actin polymerisation and membrane ruffling which allows bacterial internalisation
Gram-positive bacteria don’t have the type III secretion system
Describe another way in which actin is manipulated by bacteria.
Bacteria (such as listeria and shigella) can polymerise actin at one pole of the bacterium forming comet tails
This polymerisation propels the bacterium through the cytoplasm
What are the three mechanisms of horizontal gene transmission?
Transformation, Transduction and Conjugation
Explain each of the three mechanisms of horizontal gene transmission.
Transformation – the uptake of naked DNA from the environment
Transduction – bacteriophages infect a bacterium and take up some of the bacterial DNA. The bacteriophage then carries the bacterial DNA to another bacterium.
Conjugation – transfer of genetic material in the form of a plasmid via a conjugation tube
What is a Pathogenicity Island?
Horizontally acquired genes that contribute to the virulence
