Microbiology Techniques: Structure and Growth of Microorganisms PDF

Microbiology techniques: Structure and growth of microorganisms Growing microorganisms Identifying bacteria Microorganisms can be grown in a culture medium, solid agar, or nutrient broth in a shape; cocci, b...

Microbiology techniques: Structure and growth of microorganisms Growing microorganisms Identifying bacteria Microorganisms can be grown in a culture medium, solid agar, or nutrient broth in a shape; cocci, bacilli and spirilla laboratory. Different species vary in their requirements. The growth medium must provide: size Requirement Function staining characteristics Water Biochemical reactions take place in solution. metabolic features Carbon Production of cell materials. antigenic features Nitrogen Production of proteins, nucleic acids and co-enzymes. genetic features. Sulphur Production of some amino acids and co-enzymes. Vitamins and minerals For enzyme activity. Laboratory conditions can provide microorganisms with their optimum pH and optimum Cell wall structure temperature to maximise growth. The shape of bacteria is due to the unique structure of their rigid cell wall containing a 3D mesh of peptidoglycan (muerin). Aseptic techniques The safe handling of microorganisms in a laboratory requires aseptic techniques to prevent contamination of: the experimenter and the environment by the microbes being grown the microbial culture by unwanted microbes from the environment. Equipment and media must be sterilised before use. Techniques include: Heat - for example, use of an autoclave set at 121°C and a pressure of 103kPa for a minimum of 15 mins; heating an inoculating loop in a Bunsen flame. Irradiation - for example, gamma radiation is used to sterilise plastic equipment which would not withstand heat treatment. Using Gram Stain to identify bacteria Gram-positive bacteria have cell walls with a thicker peptidoglycan layer which retains the crystal violet/iodine complex within their cells when washed with alcohol and so stain purple. Gram staining outline procedure On treatment with alcohol, the Gram-negative cell walls lose their outer Heat to fix bacteria onto slide → stain with crystal violet → treat with iodine → decolourise with alcohol → lipopolysaccharide membrane, and the thin inner peptidoglycan layer is exposed. counterstain with safranin. This means the crystal violet/iodine complex is washed out. They stain red with the counterstain safranin.