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Molecular Genetics and Microbiology
William Navarre

Lecture 13- Transcript MGY377 NOTE: The number prior to the information describes a certain point in the lecture slides the lecturer addresses. Slides that were skipped means that the prof just read off of them and didn’t add anything new. They should still be considered testable. Bacterial cell death, injury, and spores Slide 3 -Who is typhoid mary? -She was a cook and was spreading this bacteria (S. Typhi) to people who ate her meals. Guess she didn’t wash her hand. They didn’t have antibiotics back then. She on the other hand never got sick. So they put her in jail to stop her from cooking. Slide 5 1. Most widespread method to control microbial growth 2. Increase the temperature, causing proteins to misfold Slide 6 -death from heath sterilization is exponential -at 50 degrees, in 40 minutes we have a 1 log drop (or a 90% kill). This one log drop is called the decimal reduction time: time it takes to kill 90% of bacteria at a given temperature. -looking at the table: 1D which is 40 mins at a temperature of 50 degrees causes 10% of survivors and so forth Slide 7 1. Moist heat can penetrate the bacterial cell better 2. Matrix/medium effects: I.e. when you consume bacteria in meat, hard to kill them such as turkey (dense meat) as they are protected by proteins and so forth. Also, if the bacteria is within a suitable pH, harder to kill them than versus a more detrimental pH to their own growth 3. Show in the next slide Slide 8 -Higher temperature= faster killing. Shows the decimal reduction time: or time it takes to give the one log drop, against temperature. -the mesophile in black: time will drop as you decrease the temperature. The higher the temperature, the less time it takes to kill the bacteria Slide 9 -Its not the pressure killing the bacteria, but the pressure is used to create the high steam. The high steam is what kills the bacteria Slide 11 -Creates an autoclave cycle. As you pull out the steam and you apply the pressure, the temperature will rise and will heat up. Then you have the sterilization time (usually 15 minutes) which kills off all your bacteria sample. Then the pressure is released and the temperature drops. With autoclave, the key thing is you are killing all the bacteria. This is different from pasteurization. Pasteurization reduces microbial numbers to a safe level. Slide 13 -You can also use radiation to kill microbes 1. Ionizing radiation: high energy, which damages DNA and proteins 2. More likely, use of UV radiation. This induces DNA damage, but these do not travel very far through solid objects or even liquids. Also used as a common disinfectant Slide 15 1. Dose of radiation that reduces a number of bacteria by 1 log (and not time) 2. Graph shows survival fraction. Amount of radiation varies from bacteria to bacteria Slide 16 -can also filter microbes from solution (physically pulling them out of the solution) Depth filter: I.e. saree method used in india to filter water. The bacteria get stuck in this meshwork of fibres and it reduces the risk of bacteria borne illness (resulting from the water supply) Membrane fitlers: Holes with different sizes and blocks the passage of certain microbes Nucleophore filter: Polycarbonate film with very small holes in it (similar concept to membrane filters except much smaller holes). Most bacteria are 1-2 microns Slide 17 -nucleophore filters in the lab (recall from CHM247). Filters away serum aggregates and microbes from the medium. Medium is quite clean. Slide 18 2. Pills, antibiotics for instance Slide 19 -Sterilization is complete destruction of microbes and can include the use of an autoclave or a flame -Disinfection: Applying chemicals to inanimate objected to essentially sterilize or inhibit growth of bacteria I.e. alcohol is a common one -Antisepsis: Apply chemicals to tissues to kill/inhibit growth I.e. rubbing alcohol -Bacteriocidal, bacteriostatic, bacteriolytic* Three key terms you should know bacteriocidal: chemical that kills bacteria without lysis I.e. formaldehyde bacteriostatic: inhibits bacterial growth I.e. refrigeration bacteriolytic: kills bacteria with lysis I.e. detergents Slide 20 -Graph shows log cell number over time -total cell counts are determined by microscopy and viable cell counts are done by plating -growth of bacteria at a culture over time. You add the bacteriostatic agent and growth stops -bacteriocidal causes death and the viable numbers drop (decrease in green line) -bacteriolytic causes both a decrease in total cell count as well as viable cell count Slide 21 2. 2 common methods to do this: Tube dilution method as well as the agar diffusion method Slide 22 -shows tube dilution method. You have tubes with rich medium. You inoculated the tubes with a little bit of bacteria and also put in different concentrations increasing to the right of some sort of antimicrobial agent. As you increase the concentration of the antimicrobial agent causes you to get to a point where there is no growth. Slide 23 -Agar diffusion method: Take nutrient rich agar plate, you inoculate the culture. Then you take these little disks soaked in antibiotics and you lay them on top. You’ll see robust bacterial growth in the agar. Around the disk however (where the antibiotic has diffused) t
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