5th lecture : 23/9/14

Topic: Preparation of specimens for light microscopy

Notes:
1) There are two ways to prepare specimens : Wet mount and Smears
2) Smear-steps involve preparing smear, fixation and staining.
3) No cover slip needed for preparing smear.
4) There are two ways of fixation : Heat fixing and chemical fixing.
5) Heat fixing can preserves overall morphology but not internal structure while chemical staining can protect cellular substances from destroy.
6) There are three types of staning method: simple staning, differential staning, special staning.
7) Simple staning required just a single staning agent.
8) Gram staning divided bacteria into two groups based on their cell wall structure.
9) Gram positive bacteria: Purple in colour, have thick peptidoglycan cell wall
10) Gram negative bacteria: Pink in colour, have thin peptidoglycan cell wall
11) Acid-fast bacteria: Bacteria that reist decolourization by both acid and alcohol.
12) Normally acid-fast bacteria will first stained with carbolfuchsin, then followed by acid-alcohol and counterstain.
13) To visualise capsules, we need to prepare colourless bacteria against a coloured background because capsules against a stained background.
14) To visualise endospore, Malachite green and safranin are used to stain the bacteria. Bacterial endospore appear green within red or pink cell.
15) To visualise flagella, mordant and carbouchsin applied to increase the thickness of flagella.

Activities: -

My own Exploration:
1) Leprosy is a chronic infection which caused by Mycobacterium leprae. This infection may causes infected people lack ability to feel pain and lost of sight.
2) Gram positive bacteria usually rod shaped bacilli. Gram negative bacteria usually round shaped coccus.
3) Helicobacter pylori are spiral-shaped bacteria that can cause peptic ulcer disease by damaging the mucous coaing that protects the lining of the stomach anf duodenum.

Reflection on this topic: I learnt a lot of staning method from this topic. We need to learn the characteristics of different microbes then only we know which staning method is suitable for them.