Today is my day of Microbiology, the one day of the week where I finish at 2pm and have a chance to get to town before the shops shut. I’d been trying to get some passport photo’s done for ages and finally managed it today! It was interesting as unlike the photobooths in the UK here it is done by a professional photographer which is pretty cool as you can see the difference in the quality of the image!
Anyways onto Microbiology, this mornings lecture was on the different types of bacteria and the interaction between the different cell walls and their environments. After a short break it was time for practical, this weeks practical was on the staining techniques used to observe the bacterial endospore. A endospore is where the bacteria forms a resistant structure around it to protect itself from things like ultraviolet and gamma radiation, temperature and off course chemical disinfectants. The spore form is often a dormant life stage in the life cycle of many of the bacteria where it occurs. Probably the best known endospore forming bacteria is Anthrax, with the spores being able to live dormantly in the soil in a field for 30 years or more until they are disturbed by a suitable host.
Obviously we’re not trusted to work with Anthrax (Baccillus anthracis) so instead we worked with Baccillus cereus which in humans causes around 2%-5% of foodborne illnesses. It is however also a probiotic bacteria and is used a feed additive to reduce the risk to humans from Salmonella in animals such as chickens and pigs.The staining method used here was the Wirtz-Conclin staining method which requires that the stain be applied whilst the slide is heated above boiling water. The endospore bacteria then when examined under a microscope will be stained green, with any other bacteria showing as red.
The next special staining method examined was the Ziehl-Neelson method which is used to stain Acid-fast bacteria. Acid-fast oranisms have wax-like nearly impermable cell walls and contain mycolic acid and large amounts of fatty acids, complex lipids and waxes. This makes them highly resistant to disinfectants. Carbolfuchsin is applied whilst the slide is heated over boiling, like with the Gram Stain method alcohol is used to destain cells, however in this case the alcohol is prepared as an acidic solution so will not penetrate acid fast cells. Another stain (malachite green) is then used to stain the non-acid fast cells a different color.
Some bacteria have a capsule surrounding the cell wall composed of polysaccharides which help the bacteria adhere to cells in the body and also protect it against the immune system. The Burri staining method is used here which shows capsules as colourless on a black background.
The rest of the afternoon and evening after getting back to town went to revision for my anatomy credit test on the pelvic limb on Thursday…