Well I’ve just finished semester 2 of vet school, now its just for exams and then I’ll have finished my first year of vet school! It’s still not really sunk in though I am looking at the lists of stuff we should know for our exams and having a moment of “how did we manage to cover all that?”. I’ve also managed to get some part time work over the summer to help with my tuition costs which I am glad about, my only problem is that there are just 24 hours in a single day.
In the next week I’ve got to catch up on my missed anatomy & histology tests from where I attended BSAVA Congress, and then the Monday after I start my finals with Latin. This is something I am not looking forward to as I really struggle with written latin as I am dyslexic so am going just give it my best shot! After that I have my Anatomy 1 final which is on the musculoskeletal system (aka all the bones, muscles and ligaments of different animals) and all the interspecies differences… This is the massive pile that I need to memorise for it!
Luckily I just need the muscles, ligaments and bones from the two big books, however one of the biggest test questions is asking what the differences are between animals. This is especially true of the skull which is composed of 17 parts with each having differences between species some of which are obvious in the shape of the head and others not so obvious with differences in the canals that the nerves and vessels lie in. Then there are differences with the muscles as different animals have different lengths of neck etc.
After this I have my Veterinary Genetics exam scheduled for the 6th June which is another big exam where I will be random asked 3 questions from a possible 80 covering different topics from dog coat colors through to the legislation for selecting which males to breed from! Its something that I find interesting however the amount of information that needs to be memorised here is absolutely staggering with the amount of different genetic diseases!
Hopefully after this exam is done I will have a bit more free time and so can write more diary posts which have been suffering with my current workload!
Today we started looking at Virology, which is the study of viruses. Within the veterinary field this is extremely important as there are significant zoonotic diseases (diseases that pass between humans and animals) that are viral. Some of the best known of these is Rabies (Rhabdoviridae), Yellow Fever (Flaviviridae), Rotavirus, and Poxiviridae which is the case of chicken pox/small pox etc.
Now the significant thing with viruses is that they are extremely small, which is because they lack the common features associated with other bacteria to allow replication and respiration. Instead viruses inject themselves into other cells which they then simply hijack to turn them into a virus replicating machine! This is because viruses are composed solely of either DNA or RNA, and depending on the family either 1 or two strands of this. Once a virus particle enters a cell, this genetic material enters the nucleus and the viral replication starts.
This leaves us with two problems when working with viruses, first of all we have the extremely small size – in some cases 100’s of times smaller than bacteria – which means to have a chance of seeing a virus we need to use an electron microscope. The second problem is actually cultivating or growing the virus, as the virus particle does not contain replication or respiration organs we cannot simply feed it like we do with bacteria. Instead when working with viruses we need to provide it with cells to use to replicate and grow in.
Now there are several different possible solutions here (some more distasteful than others) however the most common method is to use kidney cells. These are prepared using sterile technique from kidneys from various dead animals. The kidney is first cut up (or pulped) into extremely small pieces, which are then washed with trypsin (a digestion enzyme) and the cells from this collected in the liquid and centrifuged. This cell solution is then spread in a single layer onto a glass culture plate and the virus particles applied for growth.
At the moment I am still unsure as to how replication occurs in these cells after the death of the body that contains them and the removal of the blood supply that feeds them… However I will find out soon as my curiosity is now raised!
Well today was interesting as we are looking at Gram positive bacteria which are different to the Gram negative bacteria that we have been studying previously. The grouping into gram negative and gram positive bacteria is the most basic step in the identification of bacteria using a technique called Gram Staining (or Gram’s method). The gram stain technique was invented by Hans Christian Gram in the Berlin city hospital in 1984 whilst working in the morgue. Hans originally designed gram staining to make it easier to view bacteria in lung tissue, and noted that it did not stain all the types of bacteria.
This phenomenon is due to differences in the structure of the cell wall when exposed to different chemicals. There are four different chemicals used in the gram stain process; a basic dye, a mordant, decoloriser, and counterstain.
The basic dye is applied first before the mordant which is a substance that increases the bond between the dye and cell wall helping to fix the dye inside the cell. This makes it more difficult to wash off the dye and in the gram stain fixes the gram positive blue colour. A decoloriser is then used which is a substance that removes the dye from the stained cells, this ability varies between the cell wall type and so only gram negative cells lose their dye. The final counterstain is another dye that is applied and fills the cells that have just been cleaned by the decoloriser giving the gram negative red colour.
How to do a Gram Stain
Doing a gram stain is one of the most basic procedures in the microbiology laboratory, and so I wanted to make sure that I had covered it here. The video below demonstrates the steps that are outlined here:
Apply bacteria to a slide, if using a culture plate add a drop of saline solution to the slide to allow the bacteria to be easily spread and then air dry this over a bunsen flame.
Fix the bacteria to the slide by passing the slide back and forth through the bunsen flame.
Apply crystal violet to the slide and let it react for 30 seconds.
Rinse the slide thoroughly under running water
Apply Grams Iodine (or Lugols solution) for 30 seconds
Rinse the slide under running water and then apply 95% ethyl alcohol for 10 seconds
Rinse the slide under running water.
Apply the counterstain; in our case carbolfuchsin for 30 seconds
Rinse the slide under running water and then allow to dry.
Examine the slide under the microscope – I prefer the 100x Oil Immersion lens here!
The video demonstrating how to do a gram stain is here: