Haematology

Anatomical Pathology

Hand washing lesson at Westburn

 

Last Thursday, I went in to Westburn armed with some agar plates. We talked about bacteria and what they do and the fact that many bacteria are helpful and useful. Then we talked about handwashing and how important it is to wash your hands, especially before eating and after going to the toilet.

Ten brave volunteers stepped up and put their hands onto agar plates, then washed their hands using the correct method, and put them onto the plates again. Check out the results........

The plates on the left of each photo are the ones cultured before handwashing for each person. Next to these are the plates cultured after the volunteers had washed their hands. You can see that there are still some bacteria left on their hands after washing, but nowhere near as many!

Blood

Here's a couple of questions for you, Room 3 aspiring scientists:
How do you think machines like this have changed the way scientists like Rosie do their jobs?
Do you think these changes are good or bad?
I would be interested in your comments, so post below.

Gram Staining - Why and How?

Gram staining is a procedure which is carried out to identify whether bacteria are Gram positive or Gram negative. This is usually the first procedure done in the process of diagnosing a bacterial infection. Gram positive bacteria have cell walls which allow the stain to absorb into the cell, so they will show up as a purple colour after the staining procedure.

The process is:

1. Prepare a slide of the sample you wish to analyse. This can be blood, sputum, tissue etc. In this case, we were using stored samples of the various bacteria so I could have a look at them.

Cultured plates

Slides

2. Once the slides have been prepared and dried, the gram staining is done. The first stain is called Crystal violet. This is applied to the slide and left there for 30 seconds.This is then rinsed off and iodine is applied for 30 seconds. This is then rinsed off and acetone is applied for 6 - 10 seconds. This takes the colour off the surface of the cells so that the only stain that will be left will be any that has been allowed into the cell by Gram positive bacteria. This is then rinsed off and a red stain called safranin is applied for 30 seconds. This is basically a stain which will stick to the bacteria so that they will show up under the microscope. It will change the colour of the Gram negative bacteria to a pink colour because there is no darker purple dye retained within the cells.

Here is a diagram of the process:

These pictures show how Gram positive and Gram negative bacteria look under the microscope:

Gram positive cocci

Gram negative cocci

Week One

My first attempt at streaking

My first day in the laboratory was spent in the microbiology lab. This is where tests are done to identify bacteria from swabs and other types of samples. I learned that streaking is not just something done by miscreants at rugby games! Streaking is a technique where samples are put onto agar dishes and the concentration of the bacteria is reduced over the dish so that individual colonies can be identified. If you just apply the swab directly onto the agar, so much grows that it is impossible to separate different types of bacteria. To streak, you inoculate (apply) one third of the agar with the original swab. Then you use a sterile metal loop and swipe it through the inoculated agar a few times and then onto the clean agar. You do this 3 times so that you are getting less and less of the original bacteria. It's actually pretty tricky, but I managed to get some good plates which had individual colonies on them.

Streaking example



One of my streaked agar plates

These are two of my better plates. I have labeled the second one with the process so you can see what I am talking about (hopefully).

Labeled agar plate