The agar changed from red to purple, and a noticeable border was present rounding the colonies that exhibited growth on the dish. The ASH agar did not yield a color change. The Imitation agar exhibited a change with S. erasures and the mixed culture, but no change with E. Coli (Table 2). Table 2. Indication of color change within the four types of agar. E. Colts. Reexamined cultureNutrientTransparentTransparentTransparentMKLRed to Perplexed to PurpleASHRedRedRedMannitolRedRed to Yellowed to Hallucinogen’s AND Discussion noticeable changes occurred during this experiment.
First, two of the twelve inoculated Petri dishes yielded no growth. In order to explain these occurrences, we must first examine the differing properties of the types of agar used. Nutrient agar is enriched to allow growth of a wide variety of bacterial cultures, thus it was expected that both of the cultures used would exhibit growth on the nutrient agar. McCracken agar (MAKE) is selective for certain types of bacteria and is known to inhibit growth of Gram-positive microorganisms.
S. erasures is Gram-positive, thus we saw no growth in the MAKE Petri dish inoculated with S. erasures.
The human blood agar (ASH) is nutrient-rich and exhibits a favorable growth environment for many bacterial species, and thus allowed growth of both E. Coli and S. erasures. Amanita agar has a high concentration of NCAA which inhibits most bacterial groups. Staphylococcus species, however, are able to grow in these conditions and S. erasures was present in the Imitation Petri disc (Banyan 2 The second change that occurred during this experiment was the change in color of the agar, which was noted to occur within four of the inoculated dishes. These color change occurrences are indicative of pH changes within the agar dishes.
The MAKE gar is both selective and differential, and is thus is able to identify lactose degradation due to the presence of a pH indicator. When a lactose-positive colony such as E. Coli is inoculated on the agar, the decrease in pH yields a change in color on the agar and the presence of a noticeable border surrounding the bacterial colonies. The Imitation agar, like MAKE, also can be used as a differential agar. The color changes on the Imitation agar are indicative of acid metabolic wastes produced by the fermentation of Imitation by Staphylococci bacteria.
This fermentation causes he agar to change from red to yellow, which is what occurred in the dishes containing S. erasures (GГјenter et al, 1998). The needle is flamed before inoculation in order to prevent cross contamination of bacteria on the medium and after to kill the bacteria collected for the culture. B. Alt is important to hold the cap of the tube in your hand, and angled downwards, because microbial contamination can occur if the cap is exposed to another surface or the open air. C.
The needle must be cooled before the inoculation because if not, the heated needle can kill the bacterial sample you are trying to collect. . Enriched media are those that have been supplemented with nutrients to allow for growth of a wide variety of microorganisms. Differential or isolate media are those that are used for differentiating or isolating particular bacterial groups based upon their metabolic properties, and do so by the addition of specific indicator compounds. Selective or inhibitory media allow for, or inhibit, specific bacterial groups based upon the addition of distinct components to the media.
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