Good vs. Bad Bacteria… (Day 36)

Microbiology enzymatic reactions

Another day of Microbiology with just a week until my first microbiology test so things are getting intense. I’ve got a ton of revision to do next weekend into the different tests used and why they are used which is slightly intimidating. Its not so much about information being complex at the moment but rather the quantity, there is just so much to learn that trying to find space for it all in my head is something that I am still working on!

This mornings lecture we looked at the different cycles necessary for bacteria to live and survive (Carbon Cycle, Nitrogen Cycle etc) and how bacteria is necessary for humans and animals to also survive. We then moved onto looking at the mechanisms of microbial pathogenicity (aka ability to caused disease). There are several different classes of bacteria

  • Saprophytes – These help break down dead organic matter and mostly do not cause disease
  • Commensals – Normal bacteria of healthy host that do not usually cause disease
  • Epiphytes – Bacteria that lives on the skin surface taking nutrition from dead cells and products from the glands of the skin
  • Mutualists – Bacteria where both the host (animal) and bacteria benefit from living together
  • Opportunistic (potential) pathogens – usually do not cause disease however may with immunosupressed or broken skin etc
  • True pathogens – Microorganisms adapted to beating the body defences against disease and usually cannot survive long outside of the body.

Now a while back a scientist called Robert Koch and Friedrich Loeffler defined a set of criteria for linking a cause (microorganism) to a specific disease as follows.

  1. The microorganism must be present in all animals suffering from the disease but not in healthy animals.
  2. The microorganism must be able to be isolated and grown in pure culture.
  3. The pure microorganism must cause the disease when introduced into a healthy animal
  4. The microorganism must be isolated and cultured from this experimentally exposed animal and be identical to the original microorganism used

These were defined back in 1890, and where a breakthrow at the time however they do not account for multiple causative agents or in fact viruses which hadn’t been discovered at the time. In addition there are microorganisms that may exist in both sick and healthy animals which invalidates the first rule. Because of this Kochs postulates have had several proposed revisions however I am not sure if any of these have been formally adopted.

The methods of infection, spread and the infectious dose of microorganisms were then also discussed before the practical. This weeks practical was based on the enzymatic (or metabolic) activity of bacetria. Obviously as a living organism respiration and nutrition are important and we can use these when testing bacteria in the lab.

Microbiology enzymatic reactions
Different tests of microorganism enzymatic activity

As I have previously said, microbiology and microoganism identification can be almost like playing a game of cleudo to identify and match as many properties of an organism as possible to then identify it. These tests not only allow the ability of a microorganism to produce specific chemicals or enzymes but also the ability of it to utilise these from its environment. It is possible to look for gas production and acidity of an organism or  for the ability for a bacteria to break down gelatinase or for the production of coagulase to produce protective barries of fibres around itself.

Hopefully today has been entertaining for you 🙂 Now I need to get on with more revision!