Characterisation of Bacteria Flashcards
which physiological factors used to characterise bacteria?
- nutritional requirements (sources of C and N; growth factor requirements eg. vitamins, amino acids)
- light requirements for facultative and obligate phototrophs
- temperature
- salinity (all marine organisms are moderate halophiles - 3.5% salt)
- pH range (acidophiles, alkaliphiles)
- oxygen requirements
- pressure
- tolerance of chemical inhibitors
give an example of a species resistant to UV light
most species of bacteria are sensitive to UV light but there are some exceptions eg. Deinococcus
how are bacteria classed based on their different optimum growth temperatures?
psychrophiles, mesophiles, thermophiles
what happens to bacteria at very low temperatures?
membrane gelling; transport processes are so slow that growth cannot occur
what happens to bacteria at very high temperatures?
protein denaturation; collapse of the cytoplasmic membrane; thermal lysis
how are bacteria classed based on their oxygen requirements?
- obligate aerobes need oxygen for growth
- obligate anaerobes do not need oxygen for growth, which is toxic for them
- facultative anaerobes will use oxygen when it is available but can grow without it
- aerotolerant anaerobes do not use oxygen but can grow if it is present
microaerophiles are damaged by atmospheric levels of oxygen but grow at low levels
what experiment can be used to distinguish an/aerobes?
- tube containing very soft nutrient agar is mixed with bacteria
- oxygen only penetrates a short way into the agar
- different an/aerobes are distributed in different patterns:
- obligate aerobes are found at the top, in the oxygenated region
- obligate anaerobes are found at the bottom, where no oxygen can penetrate
- facultative anaerobes are found throughout the agar but particularly in the oxygenated region
- aerotolerant anaerobes are found evenly distributed throughout the agar
- microaerophiles are found just below the oxygenated region
what are bacteria called that grow best at high pressures?
barophiles; often deep-sea bacteria
extreme barophiles will not grow at normal atmospheric pressure
many barophiles are also psychrophiles (deep sea water is 2-3C)
what does pressure affect in the cell?
enzyme-substrate binding; membrane binding
what chemical inhibitors can be applied to bacteria in order to characterise them?
- respiratory inhibitors - Gram-positive bacteria are resistant to sodium azide (NaN3) while Gram-negative bacteria are sensitive
- chaotropic agents - Pseudomonas is resistant to phenol
- antibiotics - Mycoplasma lack a cell wall and are therefore resistant to antibiotics
what are biochemical tests?
tests for specific enzymes or metabolic pathways
what are fermentation and oxidation reactions?
fermentation - anaerobic breakdown of sugar into smaller molecules; release of waste products that are characteristic of different species
oxidation - aerobic breakdown of sugar to CO2 and water
what biochemical tests can be carried out on bacteria in order to characterise them?
1) oxidation/fermentation test
- inoculate soft agar + sugar + pH indicator and incubate
- colour change of entire agar indicates fermentation reaction eg. E. coli
- colour change just at top indicates oxidative reaction eg. Pseudomonas
2) catalase test
- H2O2 added to bacteria
- bubbles of oxygen signify presence of catalase eg. Staphylococci
- no bubbles signify absence eg. Streptococci
3) urease test
- any bacteria containing urease will catalyse the reaction urea —–> NH3
- this will result in an increased pH, which can be measured using a pH indicator
what are serology tests?
the detection of bacterial antigens using specific antibodies that can be labelled fluorescently or tested eg. if they agglutinate
what is bacteriophage typing?
- lawn of bacteria on agar
- drops of different phages
- phages that infect and lyse bacterium produce a clear zone
- bacteriophage are specific in their infection and so the test can be used to characterise bacteria
