P1/05 Microbiology Practical Exam

P1/05 Microbiology Practical Exam
Date : 22/03/2006
Time : 9.30a.m. - 10.30a.m. & 11.00a.m. - 12.00 p.m.
Venue: MDL 1234

Yup... Microbiology Practical Exam, in which we would be given a case presentation of a patient with a certain infection and we were supposed to identify the particular microorganism. My session was in the early morning, i.e. from 9.30a.m. to 10.30a.m.

So, since it was an open-bookprac exam and I had already studied for it on the previous day, I thought it was going to be pretty easy. Too bad it didnt turn out as what I wished for...

The bacteria of my case caused Conjunctivitis. When I arrived at my bench, I saw a Mac Conkey agar plate. I was quite happy, because supposingly, Mac Conkey agar is selective for Gram Negative bacteria. However, I saw the indication that one of the components that inhibit the growth of Gram Positive bacteria, i.e. the crystal violet was removed. So, I started to wonder whether the light-purple-coloured bacteria colonies could be Gram Positive one or not, since they didnt indicate whether or not the bile salts (another component that would inhibit the growth of Gram Positive bacteria) were removed. So, I was slightly confused but I decided to proceed with the Gram staining procedure first before making any conclusion.

After the gram-staining procedure, I observed the bacteria under the microscope to check whether it was Gram Positive (blue or purple) or Gram Negative (Red or Pink). Since I am not colour blind, I thought it would be pretty easy to differentiate the colour. Who knows the colour appeared as in between dard red and purple. So, again, I was confused. But most of the bacteria clumping appeared as diplococcus. So, I decided to take it as Gram Negative Nesseria, which should give me a positive Oxidase Test and a positive Catalase Test.

I wasnt confident with the Oxidase Test, as I had no experience at all in performing the test. Anyway, the bacteria gave me a negative results. SH*T!!! I was totally confused by the result. I decided not to waste time and to proceed with the Catalase Test. Luckily I managed to get a positive result. So, now... if the bacteria were of Neisseria species, why didnt they gave me a positive Oxidase Test result?????

I decided to perform another Oxidase Test, which in the end gave me a negative result as well. SIGH... So, I thought it would be better for me to perform another gram staining in order to reconfirm whether the bacteria were Gram Positive or Gram Negative. Again, the bacteria appeared as Dark Red / Purple under the microscope. ARGH!!!!!!!!!!!!!!!!!!!

Time was running out!!!!! 3 more minutes before the end of the exam, yet I was still unable to identify the microorganism. I was reluctant to take it as Staphylococcus, because Staphylococcus is a Gram Positive bacteria, and they are not supposed to grow on a Mac Conkey agar plate. GOSH!!!!! I continued to perform the THIRD Oxidase Test, but it gave me a negative result again. HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

At this point of time, our "Mario" lecturer had already dismissed us from the lab. Sob sob... So I finally decided to take it as Staphylococcus and passed up the answer sheet. I was the last one to exit the lab after swabbing the bench and "chin-chai-ly" washed and disinfected my hand with Hibiscrub.

When I discussed it with my other frens who got the same case as well, they told me that they faced the same problems as well. Sigh... I was so panic and lost after the prac exam. But some of my frens told me that Staphylococcus should be the correct answer. Then, I immediately rushed to surf the net for the correct answer after the quarantine session, and phew... indeed, staphylococcus was the correct answer. Hehehe... What a relieve, man!!

Streptococcus (chain) and Staphylococcus (clump) aureus

Haha... So that was basically my disastrous practical exam le... (-_-"')