lab_05_pure_culture_techniques - Miramar College Biology...

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Lab Exercise 5: Pure Culture Techniques Page 1 of 3 Miramar College Biology 205 Microbiology Lab Exercise 5: Pure Culture Techniques Background As you learned while investigating the ubiquity of bacteria, microbes exist everywhere and very rarely do they occur as a single species. Robert Koch was one of the first to recognize that isolating a microbe (in his case, a bacterium) away from other microbes was crucial for his own argument that microbes cause disease, as well as for understanding the characteristics of the microbe itself. His studies on Bacillus anthracis contributed to many of the laboratory techniques we still use today, including the method for isolating pure cultures of bacteria. The most commonly used method in the laboratory for isolating microbes is the streak plate and, to a lesser extent, the pour plate (Figure 1). Both methods rely on the dilution of bacterial cells in a sample to the point at which a single cell can divide separately from the rest of the population, giving rise to a single pure colony . Because the colony is the result of the reproduction, or binary fission , of a single bacterial cell, the colony is actually millions of clones of that original cell and these identical copies of the original cell and can be used for further study. For each of these methods the culture is diluted, although the method of dilution for each is unique. During the streak plate method, dilution is achieved directly on one single plate as you drag colonies along the surface of the agar with your inoculating loop. The pour plate method, on the other hand, employs the inoculating loop in a series of diluting steps in the media and the plating of the diluted samples. Both of these methods have benefits and drawbacks. The streak plate requires more skill, but uses fewer media and is less time consuming. The pour plate on the other hand requires less skill, but uses more supplies and is more labor intensive. In addition, the pour plate technique allows the researcher to examine both the aerobic and anaerobic growth characteristics of the isolates. Figure 1:
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This note was uploaded on 12/23/2009 for the course BIO 205 taught by Professor Murphy during the Fall '09 term at Miramar College.

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lab_05_pure_culture_techniques - Miramar College Biology...

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