Bacteria culture media.docx

Types of bacterial culture Liquid culture Has a growth media to allow for the growth of the organism. Differential media to distinguish between different organisms. When the media is cloudy, it indicates bacterial growth. Can be Luria broth or cooked meat media. Solid culture Non-selective= allows g...

Types of bacterial culture Liquid culture Has a growth media to allow for the growth of the organism. Differential media to distinguish between different organisms. When the media is cloudy, it indicates bacterial growth. Can be Luria broth or cooked meat media. Solid culture Non-selective= allows growth of most organisms. Can be selective to grow specific organisms. Chromogenic= colourful plates for specific organisms. Some bacteria produce hemolysins that lyse the red blood cells and degrade haemoglobin. 3 types of haemolysis on blood agar. Alpha haemolytic= reduction of red blood cells haemoglobin to methaemoglobin. Beta haemolytic= complete lysis of red blood cells Gamma haemolytic= lack of haemolysis. Selective culture media Elective agents Encourages growth of desired organism Selective agent Desired organisms are resistant. E.g. antibiotics Differential agents Discriminate between desired organisms. pH indicators e.g. of differential media called XLD agar. Used to isolate suspected salmonella. Appears black. Sodium thiosulfate in the agar is used to prevent the growth of gram-positive bacteria. Can also differentiate between e-coli and salmonella. Another e.g. of selective and differential media is MacConkey agar. Used to isolate gram-negative bacteria and to differentiate from lactose fermenting to lactose non-fermenting bacteria. Another e.g. of selective and differential media is Mannitol salt agar. If organism can ferment mannitol, it produces an acidic by-product which causes phenol iin the agar to turn yellow. CHROMagar MRSA Isolation and differentiation of methicillin resistant S.aureus including low level of MRSA. It goes from rose colour to mauve. MRSA is inhibited and other bacteria comes colourless or inhibited. Chromogenic agar Preparation of culture media. Water is added to the already mixed agar powder with nutrients and sterilised in autoclave. Autoclave reaches temperature of 121 C and 15 psi. Uses steam to sterilise. The ready agar plate is then inoculated with the samples using streak plate technique. How is number of bacteria counted using dilution method?