Lab__2a_Media___Culture_-_Collecting_Bacterial_Samples

Image mcconkeys mannitol salt blood agar specialized

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Image: McConkey’s, Mannitol Salt & Blood Agar specialized media, T. Port From the Virtual Microbiology Classroom on ScienceProfOnline.com
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Differential & Selective Specialized Media Q: What does selective mean? Q: What does differential mean? Image: McConkey’s media growing E. coli , T. Port From the Virtual Microbiology Classroom on ScienceProfOnline.com
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MacConkey's (MAC) MacConkey’s media is both selective & differential . 1. Selective because it only grows Gram-negative bacteria . Inhibits the growth of Gram-positive bacteria. 2. Differential because neutral red (pH-sensitive dye) and lactose (type of sugar) have been added to media. - Bacteria that use lactose for food (lactose fermenters) , produce acidic metabolites that trigger the pH sensitive dye to turn pink. - So lactose fermenting bacteria will grow in bright pink colonies while non-lactose fermenters will be colorless and clear. Q: Regardless of the color of the plate, what do know about bacteria found growing on MacConkey’s? Q: If there is growth, what additional information is provided when the color of the bacteria is examined? Enteric bacteria are the most frequently encountered bacteria isolated from many types of clinical specimens. They are most commonly lactose fermenters. Image: McConkey’s growing Salmonella on the left, and E. coli on the right, T. Port From the Virtual Microbiology Classroom on ScienceProfOnline.com Watch VIDEO : How to Interpret MacConkey’s Agar (MAC)
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M annitol Salt (MSA) Mannitol Salt media is both selective & differential . 1. Selective because it has a high NaCl (7.5%) concentration, and few types of bacteria can grow on this hypertonic medium. Members of genus Staphylococcus are halophilic, and grow well on this media. 2. Differential because this medium contains a pH -sensitive dye to identify organisms that ferment mannitol. Organic acids wastes mannitol fermenters produce change the medium from red to yellow. MSA works well for identifying pathogenic staphylococci , such as Staphylococcus aureus , which will ferment mannitol. Most non-pathogenic staphylococci (Staphylococcus epidermidis) will not ferment mannitol. Q: Regardless of the color of the plate, what do know about bacteria found growing on Mannitol Salt? Q: If there is growth, additional information can then be obtained about bacteria growing based on color of the medium. Images: Sterile Mannitol Salt Agar & Positive & negative differential reaction on Mannitol Salt Agar, T. Port From the Virtual Microbiology Classroom on ScienceProfOnline.com Watch VIDEO : How to Interpret Mannitol Salt Agar (MSA)
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Blood agar (BAP) Most specimens received in a clinical microbiology lab are plated onto Blood Agar . It is an enriched medium that will grow
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