6.1-6.6 Microbial techniques, Bacteria as pathogens, Antibiotics etc Flashcards
(48 cards)
what is a ‘culture’
microorganisms that have been provided with the nutrients, level of oxygen, pH and tempertaure they need to grow in large numbers so they can be observed and measured.
what is a ‘medium’
a mixture of substances that promotes and supports the growth and differentiation of microorganisms.
What is aseptic technique
involves only introducing desired bacteria into the medium under sterile conditions in order to prevent the unwanted growth of organims.
why is aseptic technique important?
- other microorganisms may harm your culture or compete with it
- there may have been contamination with a pathogenuc microorganism
- even if you think the bacteria are non-pathogenic, there may be a mutant strain present that is
describe aseptic culture technique
6 points
this kind of q can be very differnt depedning on the specific task- so these are general pointers
(eg q Describe how you would use aseptic techniques to transfer bacterial cells growing on an agar plate to a tube containing a sterile broth)
- disinfect surfaces
- work near Bunsen flame
- flame the top of any tubes (or bottles)
- flame the inocculating loop
- open the lid of the medium for as little time as possible and only open it to the very minium you need
- allow the inoculating loop to cool down before you touch microogranisms with it as they will die if its too hot
What are the three types of medium
- agar (solid)
- broth (liquid)
- selective medium
what is a selective medium
medium containing a very specific balance of nutrients-this means only very specific bacteria will grow in it and mutant strands won’t
pros and cons of using broth media
pros:
can provide oxic or anoxic conditions depending on the depth which helps identify microbes by optimum conditions
also can grow large volume of bacteria
cons:
can’t get pure discrete colony for study
Describe the growth curve of a microogranism in a closed culture
lag phase
the microorganisms are adapting to their new environment and reproduction rate increases slowly
log (exponential phase)
microorganisms grow at their maximum arte as long as there are sufficient nutrients
stationary phase
death rate=reproduction rate (due to build up of toxic waste products and waining nutrients)
death phase
death exceed new cell population as conditions continue to deteriorate
how can bacterial growth be measured (3 ways)
- cell count
- tubidimetry
- dilution plating
what things could you do to identify a specific bacteria
(- first you need to isolate it from the pateint (vomit/faeces/ food they consumed if it way say salmonella) )
- look at the colonies to see if they have a characteristic of said bacteria (like certain shapes texture colour etc)
- use gram stain to show presence of gram positive or negative bacteria (staph eg gram +ve)
- grow on selective media that identifies that bacteria (staph) or eliminates other bacteria
- use antibiotics against that bacteria
in a question it would likely tell you the type of bacteria, relate each type of test back to THAT BACTERIA its in CURLY BRACKETS so eg use antibiotics against Staphylococcus
be obvious - really spell it out
how does streak plating let you isolate bacteria
3/4 points
- culture/colonies is spread out on the agar plate
- because this seperates out individual bacteria
- so that colonies are discrete/seperate
- so only one type of bacteria can be picked up
how can cells be counted
using a haemocytometer
what is a haemocytometer
a thick microscope slide engraved with a grid and a rectangular chamber that holds a standard vol of 0.1mm3
what is a c-chip haemocytomter
a haemocytomometer that is
- disposable
- non-breakable
- reusable within limit
how can haemocytometers be used to count only viable cells?
trypan blue is used as a stain which stains dead cells blue
dilute your sample with trypan blue in 1:1 ratio
advantages and disadvantages of cell counting (with haemocytometer)
+ve: you can distinguish between viable and non-viable bacterial cells
-ve: time consuming and equipment is expensive
how do you count cells on a haemocytometer (what counts as in and which squares do you count)?
if a cell overlaps a line, count it as “in” if it overlaps the top or right-hand line and “out” if it overlaps the bottom or left-hand line
count in the 4 corner squares and the central big square
how does tubidimetry work?
it is a specialised form of colorimetry. As turdidity increases, transmission descreases and absorbance (measured in Au) increases.
This value can be linked to cell count by measuring absorbance of samples with a known cell count (via counting cells with a haemocytometer or using dilution plating) and using a calibration graph to obtain the cell count in an unknown sample.
define ‘turbid’
opaque/cloudy/thick with suspended matter
