r1

Discussion

Q4The colony morphology of the organism could be observed on the agar plate after incubating for 37 °C. On the other hand, Gram staining was carried out to recognize the cellular morphology of the desired microbes. On Nutrient Agar (NA) plate, there was growth of B. megaterium, E. coli and P. vulgaris. These three types of bacteria can grew on NA plate because it is a supportive agar that enhances the growth of non-fastidious organism. The MAC agar plate containing B. megaterium, E. coli and P. vulgaris had a growth of P. vulgaris and E. coli. There was no growth of B. megaterium on the MacConkey plate. The colour of the E.coli colonies was pink while P. vulgaris growth appears beige colour. Q3 and Q4 MacConkey (MAC) agar is a medium in which selective to Gram negative bacteria and able to distinguish between fermenter bacteria and non-fermenter bacteria as well as pathogens. MAC agar contains peptone, crystal violet, pH indicator, lactose and bile salt (Sumbali and Mehrotra, 2009). Peptone is a source of protein for microorganism growth. Crystal violet and bile salt are the inhibitory agents that suppress the growth of Gram positive bacteria but support most of the enterococci Gram negative bacteria (Sumbali and Mehrotra, 2009). Thus, the results illustrated that B. megaterium which is a Gram positive bacterium cannot grew on the plate. On the other hand, E.coli and P. vulgaris formed colonies on the plate. This indicates that MAC agar consists of selective properties. The colony of E.coli was pink colour because it was a lactose fermenter while P.vulgaris was non-lactose fermenting bacteria formed beige colour.

Q3 and Q4The lactose present in the agar is a fermentable sugar in which provide a ca...

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...h the bacteria on the agar plate. If the plates are incubated for more than 24 hours, some of the organisms which ferment lactose late (enterbacteria) will tend to appear pink colonies on the agar plate. Hence, these organisms can be mistakenly considered as a lactose fermenter despite the fact that the organisms are non-lactose fermenter (Goodman and Pickett, 1966).

Conclusion

Selective and differential media such MacConkey media is commonly used to identify bacteria and also determine potential pathogens. MAC media is used to suppress the B. megaterium while allow the growth of both P.vulgaris and E.coli. It is helpful in identifying the growth pattern of the bacteria in which it can be applied in variety application such as food analysis. Lastly, most of the microorganism able to form colonies on the nutrient media as it supplies essential source for microbes.