BIO 175 LAB PRACTICAL

McKenzie Harrelson

Date Due: March 12, 2015 (DE02)

COLONY APPEARANCE

The colony I isolated was small (about 2.0 mm), round, yellow in color, convex, and was shiny. The size of my colony (small) was borderline between small and large. It could be either size, and if it incubated another day it may have grown larger.

CELL APPEARANCE

When I Gram-stained a sample from my colony and magnified it under 1000x, the cells I observed were rod-like and red. From this I concluded that the cells were Gram-negative bacilli.

DEXTROSE FERMENTATION

PURPOSE:

To determine if the bacterium isolated is capable of microbial fermentation of the sugar dextrose. Bacteria that ferment dextrose produce organic acid as a by-product causing the pH to lower, causing the phenol red to change to yellow. If there is no change in color the bacteria will likely have no fermentation of the sugar dextrose. In addition to producing acid, some bacteria will produce carbon dioxide in the form of an air pocket or bubble in the Durham tube. If an air pocket or bubble is observed int he Durham tube gas has been produced. If there is no gas in the tube, then it is likely no gas had been produced.

OBSERVATION:

The bacteria I isolated and tested for the fermentation of the sugar dextrose turned the phenol red liquid to an orangish-yellow color, and there was a gas bubble in the Durham tube.

CONCLUSION:

The bacteria I isolated is capable of fermentation of the sugar dextrose and produced a gas as well.

MOTILITY

PURPOSE:

To determine if the bacterium that has been isolated is capable of motility. If the tube is turbid, this indicates that the bacteria have moved away from the stab mark. If the stab mark is clearly visible and the tube is not turbid, then the bacteria is likely nonmotile.

OBSERVATION:

The bacteria I isolated moved away from the stab mark and caused the tube to look turbid.

CONCLUSION:

The bacteria isolated in my sample were motile.

SUMMARY OF TEST RESULTS:

COLONY SIZE: Small COLONY ID: Escherichia coli

CHARACTERISTICS

Gram stain
Gram-negative
Dextrose fermentation
Acid and