Exercise 6 : Quantitation Of Microbial Population

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Report 2: Exercise 6 – Quantitation of microbial population
Contamination by bacteria and foodborne disease is one of the most widespread problems these days. Determination of microbial population is among the most fundamental procedures in microbiology and the quantitative determination of microorganisms is critical especially in food microbiology procedures to ensure safety of consumer. Numbers of potentially hazardous microorganisms from effects of the whole food product process can also be obtained from microbiological challenge testing or predictive microbiology. The current techniques which are widely used are viable count, total cell count and turbidometry. The most common as well as the most sensitive technique is
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The growth of microbial in a clear liquid broth will increase both the turbidity and absorbance of the broth, and the changes are detected and measured by a turbidometer. Total cell count is a direct counting method which includes microscopic counts with a hemocytometer or a counting chamber. Hemocytometer or counting chamber usually consists of volumetric grid divided into differently sized cubes for accurately counting the number of microorganisms in a cube and for the calculation of concentration for the sample. A drop of sample from homogeneous suspension is added under the coverslip and viewed under microscope for counting (Adds et al., 2005). This technique is faster and requires lower cost but it is not able to distinguish between living and dead cells, therefore it is known as direct counting method.
To quantitate microbial population by carrying out two different techniques and perform calculations based on each technique, to investigate the accuracy associated with each technique and identify the most appropriate use of each technique.
Refer to BTH2830 Laboratory manual pg. 53-56 (MIC 2011, Class Notes, 2005)
Table 1: Raw data for number of colonies count in pour plates and spread plates with dilution factor of 10-6 , 10-7 and 10-8.
Group Pour Plate Spread Plate
HK Dilution Factor Dilution Factor 10-6 >300 >300 10-6 201 253 10-7 300 10-6 >300 283 10-7 51 43 10-7 36 40 10-8 s

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