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00:00:01 | 00:00:02 | >> Instructor: This stream cast is created to |

00:00:02 | 00:00:06 | show you how to solve this dilution schedule problem. |

00:00:06 | 00:00:09 | Preparing a dilution schedule for spread plates |

00:00:09 | 00:00:11 | using 10 to the minus two dilutions, |

00:00:11 | 00:00:13 | and starting with a culture of E.coli |

00:00:13 | 00:00:16 | three point three times 10 to the eight |

00:00:16 | 00:00:18 | cells per milliliter. |

00:00:18 | 00:00:21 | First thing we need to do is pull the information |

00:00:21 | 00:00:23 | we can out of the wording in the question. |

00:00:23 | 00:00:26 | So the first we need to know rest for spread plates, |

00:00:26 | 00:00:31 | our plate counting range is gonna be between 20 and 200. |

00:00:32 | 00:00:34 | Because it's spread plates we're only allowed to |

00:00:34 | 00:00:37 | plate zero point one mil of our dilutions |

00:00:37 | 00:00:39 | into the petri dishes. |

00:00:39 | 00:00:42 | This means the dilution in the petri dish |

00:00:42 | 00:00:45 | is gonna come from a tube that is has a dilution |

00:00:45 | 00:00:48 | that is one number lower than the dilution |

00:00:48 | 00:00:50 | we want in the plate. |

00:00:50 | 00:00:52 | So we're gonna figure out |

00:00:52 | 00:00:55 | what our target and our bracket dilutions are. |

00:00:55 | 00:00:57 | By doing this we figured out that we're going |

00:00:57 | 00:00:59 | to need two plate, 10 to the minus six, |

00:00:59 | 00:01:02 | 10 to the minus seven, and 10 to the minus eight, |

00:01:02 | 00:01:04 | to get our targets in our brackets. |

00:01:04 | 00:01:07 | Let's draw out our tubes that we have here. |

00:01:07 | 00:01:09 | So we have our culture. |

00:01:09 | 00:01:10 | We're gonna do as many |

00:01:10 | 00:01:13 | 10 to the minus two dilutions as possible. |

00:01:13 | 00:01:15 | So we're gonna start with point one mil |

00:01:15 | 00:01:16 | into nine point nine. |

00:01:16 | 00:01:19 | That'll give us our 10 to the minus two dilution. |

00:01:19 | 00:01:21 | Point one mil in nine point nine |

00:01:21 | 00:01:25 | will give us our 10 to the minus four dilution. |

00:01:25 | 00:01:28 | But going forward we need to change our dilution schedules. |

00:01:28 | 00:01:32 | If we look at our targets we need a minus eight dilution, |

00:01:32 | 00:01:35 | minus seven dilution, and a minus six dilution. |

00:01:35 | 00:01:38 | Those have to come from tubes that are one dilution lower. |

00:01:38 | 00:01:40 | So we need to create dilutions that are |

00:01:40 | 00:01:44 | 10 to the minus five, minus six, and minus seven. |

00:01:44 | 00:01:47 | Those can't be created with using only |

00:01:47 | 00:01:48 | 10 to the minus two dilutions. |

00:01:48 | 00:01:50 | So we need two dilutions that are gonna have |

00:01:50 | 00:01:55 | one mil into nine creating a 10 to minus one dilution. |

00:01:55 | 00:01:58 | So we write our dilutions in our cell count so we can see. |

00:01:58 | 00:02:01 | We're gonna make 10 to the minus two, 10 to the minus four, |

00:02:01 | 00:02:04 | 10 to the minus five, six, and seven, |

00:02:04 | 00:02:05 | are going to be created there, |

00:02:05 | 00:02:07 | so that we have the dilutions we need |

00:02:07 | 00:02:10 | to get onto the plates that we have. |

00:02:10 | 00:02:13 | Our dilution plates will be written up this way. |

00:02:13 | 00:02:15 | Our bracket plate of 10 to the minus six |

00:02:15 | 00:02:18 | will have 330 colonies. |

00:02:18 | 00:02:20 | Our target plate of 10 to the minus seven |

00:02:20 | 00:02:22 | will have 33 colonies. |

00:02:22 | 00:02:25 | And our last bracket plate with 10 to the eight dilution |

00:02:25 | 00:02:27 | will have three point three colonies. |

00:02:27 | 00:02:29 | Because we can only plate zero point one mil, |

00:02:29 | 00:02:32 | we can draw that on now. |

00:02:32 | 00:02:35 | Our 10 to the minus eight plate is |

00:02:35 | 00:02:38 | taking a sample out of our 10 to them minus seven tube. |

00:02:38 | 00:02:41 | Our 10 to the seven, minus seven, plate comes from |

00:02:41 | 00:02:43 | our 10 to the minus six tube. |

00:02:43 | 00:02:46 | And 10 to the minus six plate comes from a |

00:02:46 | 00:02:49 | 10 to the minus 5 tube, always one dilution lower. |

00:02:49 | 00:02:51 | And this would be the correct solution. |

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