Microbio lab report body

2609 words 11 pages
Maura Gongora
12th December, 2014
MCB 3020L- Section 018
Unknown #16

This report contains the background information on gram positive and gram negative bacteria, which will aid in understanding the use of specific laboratory experiments to distinguish between the two types of bacteria. Included are the materials and methods used to identify the gram positive and gram negative bacteria and methods which also differentiate between microbes of each group. The implications of the methods of identification used are also described in this report to give an explanation as to why a certain route was taken in carrying out experiment 14. The results of the experiment carried out for the identification of three unknowns are tabulated
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The TSI tube contains glucose, lactose and sucrose along with phenol red indicator to determine whether the bacteria can ferment the sugars. If gas is produced, a break in the agar is observed and if sulfur was reduced to H2S, black precipitation is observed on the media. All media were then incubated at 37°C for 24 hours and stored in the lab’s refrigerator. (Carson, 2013)
The third week of the experiment was mainly used for recording the final data and analyzing the information to eventually identify the three bacteria in the mixed culture through a process of elimination.

The following flow chart was used in determining the identity of the bacteria in the unknown mixture:

Table 1. Flow Chart Showing the Identification of Five Gram-Positive Bacteria and Four Gram-Negative Bacteria


The results for the first week included the colony growth on the TSA plate, BAP, and Mac Plate.
There was growth from the three bacteria on both the TSA plate and the BAP. On the TSA plate, Unknown A colonies grew with a pinpoint shape, white color, and small size, Unknown B colonies grew with a circular shape, transparent color and medium size; and Unknown C colonies grew with an undulate shape, white color and large size. On the BAP, Unknown A colonies grew with a pinpoint shape, white color and smooth surface, Unknown B colonies