GMED1000 Lecture Notes - Lecture 7: Mannitol, Peptidoglycan, Growth Medium
9 Aug 2018
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Diaphragm: controls amount of light entering the condenser. For unstained preparations, contrast can be increased by closing the condenser diaphragm. Other types of microscopy include fluorescent, electron, etc. Simple stains: all components stained the same colour. Results based on cell wall composition of the bacteria. Fixation: heat fix smear on side (bacteria aren"t dead) Crystal violet: crystal violet (30 seconds, stains all bacteria) Iodine molecules bind to crystal violet to create a larger molecule(30s, fixes stain) iodine molecules too large to pass through peptidoglycan in cell wall stays in cell, staining it purple. Counter stain safranin: carbol fuchsin (30s) counter stain. Site of sample dictates types of agar used. Pure cultures are the best for iding unknown organisms. Selective media only allow certain bacteria to grow while inhibiting others. Differential media contain substances that will allow different bacteria to be distinguished from each other. Mannitol salt agar (msa) is selective for staphylococci.
