Biochemical Tests


Importanceof a pure culture in biochemical tests

Apure culture should be used in biochemical tests to ensure that theresearcher grows only the correct bacterium that is being targeted(Vasanthakumari, 2009). A pure culture also ensured that thebiochemical experiments are conducted free of any contamination thatmight interfere with the accuracy of results. For example, a culturecontaining unwanted microorganisms can skew the findings of abiochemical experiment by producing false negative or positiveresults.

Importanceof culturing an organism in different types of media

Differenttypes of media are used to distinguish one type of microorganism fromanother. This idea is based on the notion that different species ofmicroorganisms grow in different conditions (Vasanthakumari, 2009). Therefore, using several types of media with specific characteristicsthat support the growth of particular microorganism is one of themost accurate means of distinguishing between microorganisms andobtaining a pure strain.

Techniqueused in isolating pure cultures from mixed flora

Streakplate method is the most effective technique used to obtain purecultures from mixed flora. This technique helps the researcher inisolating and sampling specific bacterial colonies by growing them onthe growth media surface. The procedure involves the use of purecultures, while the transfer of colonies that have been successfullyisolated is done with a sterile swab (Vasanthakumari, 2009). A Bunsenburner is used to sterilize the swab. Sterilization of the swab isdone any time different zones of are to be streaked. The number ofmicroorganisms deposited during the streaking process decreases fromthe starting point towards the ending point. Types of streakingmethods include four quadrants and three sectors streaking.

Thecharacteristics used to distinguish bacterial colonies

Bacterialcolonies appear like solid masses when grown on nutrient media andviewed with naked eyes. However, there are several characteristicsthat can be used to distinguish between these colonies. First, theshape of each colony can be used in predicting the specific type ofbacteria growing on the nutrient media. This is because differenttypes of bacteria grow in different shapes, such as filamentous,round, or irregular (Simone, 2013). Secondly, different types ofbacterial colonies have different types of edges (such as smooth orirregular edges), which can be used to distinguish between them.Third, Different types of bacteria produce colonies with differenttypes of color (such as purple, green, or red), which is an importantcharacteristics that can be used to different between differentbacteria. Fourth, opacity can be used to distinguish betweendifferent colonies because different bacteria produce colonies withdifferent levels of opacity, such as iridescent, transparent, ortranslucent.


Simone,L. (2013, October 30). What is the technique used to isolate culturesfrom a specimen that contains mixed flora. E-NotedIncorporation.Retrieved September 21, 2014, from

Vasanthakumari,V. (2009). Practicalmicrobiology.New Delhi, DL: BI Publications Pvt Ltd.