Question

 

Describe the expected results for your bacterium (i.e. relative amount of growth compared to control; color changes in bacteria and/or agar, presence of gas, clear zones, etc.)

Analysis/Result: Explain what these results indicate. (i.e. This organism is Gram positive or Gram negative and ferments lactose, maybe a member of Enterobacteriaceae)

Answer 1

Staphylococcus epidermis are gram positive bacteria . They live best in aerobic condition. But other strains like facultative anaerobes are also there. The strain which you have can be identified only from the results of your thioglycollate broth test.

Again whether it is a gram positive or gram negative bacteria can be explained only based on gram staining. From thioglycollate test one can identify only the oxygen requirement of bacteria and can differentiate it accordingly.

Thioglycollate broth test is done to differentiate aerobic and anaerobic bacteria. In the thioglycollate broth an oxygen grading condition is there because thioglycollate added will absorb oxygen and water will be produced. The maximum Oxygen will be in the top and no Oxygen will be in the bottom of the tube. Hence we can differentiate the aerobes and anaerobes based on the position of growth. Obligate aerobes will grow in the top and obligate anaerobes will grow in the bottom and facultative anaerobeic bacterial growth will be seen diffused in the tube.

The purpose of agar is to maintain an oxygen less or anaerobic system deeper in the tube.

Usually an indicator resazurin is added to the broth. Resazurin is pink in colour in presence of Oxygen and colour less in the absence of oxygen. While conducting the test the cap of tube is loosely closed hence there will be oxygen in the top and the colour over there will be pink and obligate aerobes will be grown there. In the rest of the portion of the tube it will be colourless.

The growth of different types of bacteria is as explained below

Obligate aerobes - growth only in the pink band that is in the top of tube.

Facultative anaerobic- growth can be seen through out the media but more concentrated on bottom of tube.

Facultative aerobes- Growth through out the media but more at the top.

Obligate anaerobes - growth seen only at the bottom.

In anaerobic conditions the bacteria will undergo fermentation and lactate will be produced