Lr Fm 5.docx

PROCEDURE Sample Handling 

All sample units were refrigerated until needed  The sample units were analysed quickly

Preparation for Analysis 

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Preparation of VRBA was carried out prior to the analysis according to the manufacturer’s instructions  Molten VRBA was tempered to 45C-48C because Pour-Plate Method was used The duplicate petri dishes were marked identifying the sample, sample unit, dilution or date of inoculation

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Preparation of Sample  Peptone Water was prepared as diluent. Serial dilution up to 10-6 dilution factor for each sample was conducted

Plating  Molten VRBA tempered to 45-48C was prepared  It was cooled before being poured into the plates  1mL od each dilution was poured into petri dishes into the plates  10mL of VRBA was poured into the plates and swirled to mix  5mL of VRBA was overlayed and it was left to be solidified

Incubation 

The solidified plates were inverted and incubated for 18-24 hours at 35C

CONCLUSION

Based on the result obtained from conducting this experiment, it can be concluded that the objectives of this experiment have been achieved successfully. For Part 1, Violet Red Bile Agar (VRBA) used the Pour-Plate Method. It can be seen from Table 1 that when the concentration of the sample was 10-1, the average number of colonies is 18 CFUs/mL while 10-5 was 8.5. This proofs the theory that when the number of colonies increases, he concentration of the sample will also increase. Next, from the plate-count data, the concentration of bacteria in the original sample is calculated. Following the rules of CFU count, the dilution factor used was 104 where the average number of colonies were 29. The number of CFUs/mL was calculated to be 2.9 x 10-6 CFUs/ml. On the other hand, MPN method was applied throughout the experiment for Part 2. The mediums used were BGLB and Mc Conkey broth. The tube is deemed as positive when the green colour of the liquid turns cloudy and when there is presence of air bubbles inside. Therefore, it can be said that the sample contains coliform. If one of them is not fulfilled, thus, the tube will be deemed as negative. For BGLB, the data for the MPN table is 3, 3, 2, 1 and 0 depending on how many positive signs obtained from each of the concentration of sample which was from 10-1 until 10-5. MPN value was calculated to be 1.5x10-3. However, for Mc Conkey broth, the MPN was 2.3x102. MPN has higher amount of coliform bacteria than pour plate method since bacteria thrives more in liquids and watery environment. Since the broth tubes were observed for the presence or absence of growth, the MPN method gives a better alternative to count the colonies. It is more beneficial because the broth can be incubated for a longer time and allows an accurate determination of the colony count. The interpretation of the MPN method was easier because the pattern of growth was observed visually. Thus, it takes less time to interpret data than PourPlate method as each plate had to be counted to get the result. Feng P. (2002). Coliform Bacteria. Retrieved on 30 March 2019 from website

https://www.fda.gov/food/foodscienceresearch/laboratorymethods/ucm064948.htm