FDE305 Food Microbiology Laboratory Techniques PDF

FDE305 - FOOD MICROBIOLOGY LABORATORY TECHNIQUES FOR ISOLATING PURE CULTURES TECHNIQUES FOR ISOLATING PURE CULTURES Pour plate Streak Plate Spread Plate ISOLATION Isolation is necessary to examine one species at a time rather than a mixture of many...

FDE305 - FOOD MICROBIOLOGY LABORATORY TECHNIQUES FOR ISOLATING PURE CULTURES TECHNIQUES FOR ISOLATING PURE CULTURES Pour plate Streak Plate Spread Plate ISOLATION Isolation is necessary to examine one species at a time rather than a mixture of many different kinds A pure culture is a population of cells or multicellular organisms growing in the absence of other species or types A pure culture may originate from a single cell or single organism, in which case the cells are genetic clones of one another ISOLATION Isolated culteres Pour Plate Technique Temper sterilized agar containing medium to 42-45°C Mix the measured amount of specimen and the liquid agar in a sterile petri plate Bacteria are distributed through the agar and grows both on the surface and in the depths of the inoculated medium Pour Plate Technique Advantages Easy to identify whether bacteria is an anaerobe, aerobe or a facultative aerobe Disadvantages Colonies of several species may present a similar appearance in the agar environment Certain species of bacteria may not grow in this environment Difficulty may be encountered in removing or picking colonies for further study Pour Plate Technique Pour Plate Technique Streak Plate Technique Rapid qualitative isolation method Involves spreading a loopful of culture over the surface of an agar plate Generally four ways or quadrant streak procedure is done Streak Plate Technique Advantages Spread millions of cells over the surface Individual cells deposited at a distance from all others Distinct colonies do not touch any other colonies Disadvantages If there is too much organism present on the inoculating loop, cells can cluster and form like one colony but it can be a couple of colonies Streak Plate Technique Using a sterile loop, take a loopful of your bacteria Streak a vertical line Then streak gently across section 1 Zig-zag pattern until a 1/3 of the plate is covered Do not dig into the agar Sterilize the loop & let it cool Rotate the plate about 90 degrees and spread the bacteria from the first streak into a second area Do only one streak (or very few) in the first area and once you are in the second area do not go back to the first Do a zig-zag pattern until the 2nd area is covered Sterilize again & do the same for 3rd area Make sure that your red hot loop is cool enough prior to touch the bacteria Stab it into the agar in a position away from bacteria to cool it Incubate the plate inverted at 37 oC Streak Plate Technique Quadrant Streak Procedure Spread Plate Technique Make dilutions of the emulsified specimen in a suitable diluent Place a prescribed volume of a dilution in the center of a dry agar plate and spread it over the medium while rotating the plate Close the petri dish and wait about an hour to dry before incubating Spread Plate Technique Advantages Useful for heat sensitive microorganisms Better for aerobic bacteria since growth occurs on the surface of the agar plate There is no condensation problem Disadvantages Limited counting range Limited inoculation volume Spread Plate Technique References ÖKMEN, Z. A., & BOZOĞLU, F. (1995). Food Mıcrobiology Laboratory Book (pp. 1-16). Ankara, Turkey: Food Engineering Department, Middle East Technical University. ENTİS, P. (2002). Food Microbiology: The laboratory. (pp.25- 49). USA,Washington DC:The Food Processors Instute.