Investigating antibiotics

• what types of growth medium can be used

  nutrient broth solution , solid agar jelly
• what will happen to bacteria grown on agar plates

  they will form visilble colonies on the surface or will spread out to give an even covering
• how do you make an agar plate

  hot agar jelly is poured into petri dish , when the jelly is cooled and set , inoculating loops can be used to transfer microorganisms to the agar jelly . alternatively , or a sterile dropping pipette and spreader can be used to get an even covering of bacteria . the microorganisms then multiply
• how do you investigate the effect of substances on bacterial growth

  place paper discs soaked in different types of antibiotics on an agar plate that has an even covering of bacteria , leave the space between the discs . the antibiotic should diffuse into the agar jelly . antibiotic resistant bacteria will continue to grow on the agar around the paper discs , but non resistant strains will die , a clear area will be left where the bacteria have died - this is called the inhibition zone , make sure you use a control , this is a paper disk that has not been soaked in antibiotics , this will ensure that the difference in inhibition zone is due to the bacteria alone , leave the plate for 48 hours at 25 degrees
• the bigger the inhibition zone......

  the more effective the antibiotic is
• how should you use aseptic techniques

  the petri dish and growth medium must be sterilised before use . this can be done by placing them in a machine called an autoclave , which uses steam at a high pressure and temperature to kill any organisms present , before being used to transfer bacteria , an inoculating loop should be sterilised by passing it through a hot flame . so that any unwanted organisms are killed , liquid bacterial cultures should be kept in a culture vial with a lid , the lid should only be briefly when transferring the bacteria , petri dish should be covered with a lid to stop microorganisms from the air coming in , stored upside down to stop condensation