microbiology Flashcards
what shape are bacillus bacteria?
rod shaped
what shape are coccus bacteria?
spherical
what shape are spirillum bacteria?
spiral
what is the structure of bacteria?
circular DNA and plasmids
70s ribosomes
peptidoglycan cell wall
flagellum
pilus
capsule
how are prokaryotes different to eukaryotes?
no membrane bound nucleus or organelles
70s ribosomes
peptidoglycan cell wall
what does the cell wall do?
prevents osmotic lysis
rigidity
cell structure
what is the structure of gram positive bacteria?
thick layer of peptidoglycan that holds dye
what colour does gram positive bacteria stain?
purple
crystal violet dye is not washed out by ethanol
what drug is effective against gram positive bacteria?
penicillin
what is the structure of gram negative bacteria?
thin layer of peptidoglycan
outer layer of lipopolysaccharide
doesn’t hold dye
what colour does gram negative bacteria stain?
pink
crystal violet dye is washed out by ethanol
what are the metabolic requirements for microbes?
suitable temperature and pH
oxygen requirements
carbon, nitrogen and inorganic ions
what is the optimum temperature for pathogens to grow at?
37 degrees
what is optimum temperature for saprotrophs?
lower than 37 degrees
what is optimum temperature for psychrophiles?
down to -15 degrees
what is optimum temperature for thermophiles?
up to 80 degrees
what are usual incubation conditions?
25 degrees
24-48 hours
aerobic conditions
what are obligate aerobes?
bacteria which require oxygen
what are obligate anaerobes?
can only grow in absence of oxygen
what are facultative anaerobes?
able to survive in absence of oxygen but grow and divide faster in presence of oxygen
what does aseptic technique do?
prevents contamination of environment by microbes being handled
prevents contamination of microbial cultures by unwanted microbes from environment
what are examples of aseptic technique?
autoglave glassware
flaming loops, wires and glass spreaders
open petri dish at small angle
roaring blue flame to create convection current
flame neck of bottle
what are streak plates used for?
use to separate mixed cultures into pure ones
what are the problems with counting bacteria and solutions?
small - use microscope
lots of them - dilute sample
alive or dead? - allow them to grow into colonies
what does total cell count include?
living and dead cells
what does viable cell count include?
only living cells
what are disadvantages of doing serial dilution to count bacteria?
possible to underestimate population due to clumping
takes a long time to count
what are advantages of doing serial dilution to count bacteria?
counts living cells
