9/18/2016 Plate Count Simple Right? Used to be referred to as the total plate count This is not accurate,Why? 35 degrees C and aerobic growth were standard but do not detect anaerobes or bacteria growing at 15 degrees C -important pathogens may go undetected Variations of the standard aerobic plate count would increase specificity for certain types of bacteria 6.5×105 Countable plate 25-250 colonies Selective and Differential Media Mannitol Salt Agar Staphylococci Selective media Selective agent-7.5%salt inhibits growth of most includes a component that favors the microbes growth of the desired microbe Mannitol fermentation -may contain an ingredient that inhibits differentiates between pathogenic and non- the growth of competing microbes pathogenic staphylococci ·Differential media 5.aureus ferments mannitol turning phenol -a component is added to the media that red to yellow enables colonies of the target microbe 5.epidermidis cannot to look different to other colonies ferment mannitol and appears red 9/18/2016 4 Plate Count 6.5 x 105 Countable plate 25–250 colonies13 Simple Right? • Used to be referred to as the total plate count • This is not accurate Why? This is not accurate, Why? - 35 degrees C and aerobic growth were standard but do not detect anaerobes or bacteria growing at 15 degrees C - important pathogens may go undetected • Variations of the standard aerobic plate count would increase specificity for certain types of bacteria 14 Selective and Differential Media • Selective media - includes a component that favors the growth of the desired microbe - may contain an ingredient that inhibits the growth of competing microbes • Differential media - a component is added to the media that enables colonies of the target microbe to look different to other colonies 15 Mannitol Salt Agar • Staphylococci • Selective agent - 7.5% salt inhibits growth of most microbes • Mannitol fermentation differentiates between pathogenic and non￾pathogenic staphylococci - S aureus S. aureus ferments mannitol turning phenol red to yellow - S. epidermidis cannot ferment mannitol and appears red 16