1. Bacterial properties Flashcards
Bacterial Forms
Cocci: Oval-shaped/ spherical
Bacilli: Rod shaped
Spirilli: Curved (gentle curve- corkscrew-like spiral)
Gram stain
Distinguishes between 2 different kinds of bacterial cell walls
Bacteria stained with a violet dye and iodine, rinsed in alcohol, then stained with a red dye.
Gram positive bacteria
Peptidoglycan in cell wall retains dye.
High peptidoglycan = deep violet
List 2 Examples of Gram+ bacteria
Staphylococcus aureus
Streptococcus pneumoniae
Gram negative bacteria
Dye is lost from thinner peptidoglcan
Have 2 membranes (more difficult to get antibiotics through)
The cells absorb counterstain making them appear pink
List 3 Examples of Gram- bacteria
Escherichia coli
Salmonella
Shigella
Mycobacteria
Have characteristics of both Gram+ and Gram-
How to identify Mycobacteria
Stain red with Kinyoun stain
Mycobacteria are acid fast
Have a high content of mycolic acids in the cell walls
List 4 Extracellular pathogens
Staphylococcus
Streptococcus
Yersinia
Neisseria
Infectivity
Organisms ability to infect
Virulence
Measure of the degree of disease that a pathogen causes
Infective dose
Amount of a pathogenic agent that will cause infections in susceptible subjects
Salmonella uses which 2 evolutionary related protein machines?
Flagellum (movement)
Injectisome (causes actin polymerisation, membrane ruffling, bacterial internalisation)
Mode of replication in bacteria
Binary fission
Gene repertoire
Genomes of bacterial pathogens encode 500-4500 proteins:
Core genes (40%)
+
Accessory genes (vary between different strains)
Vast majority of accessory genes acquired by…
Horizontal Gene Transfer
HGT- Transformation
DNA uptake and integration by homologous recombination
e.g. Neisseria
HGT- Conjugation
Physical bridge between bacteria allows the transfer of a plasmid between the bacteria
Many Gram+ and Gram-
HGT- Phage Transduction
Phages infect bacteria and replicate their DNA
Cuts bacterial DNA into small pieces
Some bacterial DNA may be packaged into the phage heads
New phage particles are released, these inject bacterial DNA from the previous bacterium into the next bacterium.
Injected DNA may be incorporated into the bacterial chromosome.
Many Gram+ and Gram-
3 Modes of HGT
Transformation
Conjugation
Phage Transduction
Pathogenicity Island
Horizontally Acquired DNA that contributed to Virulence
List 6 examples of Intracellular pathogens
Salmonella Mycobacteria Chlamydia Listeria Shigella Coxiella
