Laboratory report: experiment 1 Culture medium preparation - Essay Prowess

Laboratory report: experiment 1 Culture medium preparation

Laboratory report: experiment 1 Culture medium preparation

Laboratory report: experiment 1 Culture medium preparation

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Question 1.

Liquid media used for culturing microorganisms in the lab is typically sterilized using a small autoclave (essentially, a programmable pressure cooker).

 

I prepare 5 litres of medium, split this into five one-litre bottles and put these into the autoclave. The autoclave is programmed for a 20 minute/121oC cycle.

 

My lazy colleague also makes 5 litres of the same medium, but instead puts the whole lot into a single large bottle and autoclaves this using the same programme.

 

A day-or-so after autoclaving, the medium in my colleague’s bottle has gone cloudy indicating that contaminating bacteria have survived the autoclaving and have grown in the medium. In contrast, the medium in all five of my bottles is clear (i.e. no bacterial growth).

 

Why do you think we have different results?

 

The 5-litre bottle is so large that heat transfer to the interior of the solution in retarded. As a result, the entire solution is not heated up to 121oC for sufficient time. By contrast, if splitting them into 1-litre bottles, the total surface area is larger such that the contents of the bottles are sufficiently heated to the required temperature within the 20-minute cycle.

 

What would you do differently if you wanted to autoclave a large volume (such as 5 litres) in a single bottle?

 

I would either programme the cycle of autoclave to be longer or set it to a higher temperature. This either allows more time for heating up the bottle, or the bottle can be heated up faster due to larger temperature difference.

 

End of report.

 

 

 

 

 

 

 

 

Laboratory report: experiment 2 Reducing bacterial contamination

 

 

 

 

 

 

 

 

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Results

Report your findings. What did the bacterial growth look like on the control (water only) plate? Which of the various treatments were effective in reducing the amount of bacteria? Was there a difference between the Gram positive M. luteus and the Gram negative E. coli?

 

The size of clear zones (diameter in mm) of different treatments were measured as follows:

bleach TCP isopropanol soap NaCl vinegar honey water
11 mm 6 mm 12 mm 6 mm none 6 mm none none
 

The data of another group using M. luteus are as follows:

bleach TCP isopropanol soap NaCl vinegar honey water
22 mm 9 mm 20 mm none none 10 mm none none
 

The class results are as follows (% of groups showing inhibition):

bleach TCP isopropanol soap NaCl

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