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Microbiology 251-11 Lab 7-8

Microbiology 251-11 Lab 7-8 - WEEK 7 February 22-24 Control...

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WEEK 7: February 22-24 Control of Microbial Growth Microbial Flora of the Hand Results Examine your streak plate from your hand plate. You should have obtained several isolated colonies, all with the same morphology indicating that you were successful in picking an isolated colony to begin with. Show your streak plate to your lab instructor who will evaluate your technique. * * * Bacterial Conjugation Results Record your results in the table below: Strain LB Media Result I - I ampicillin I streptomycin I ampicillin + streptomycin II - II ampicillin II streptomycin MCRO 251 Lab Manual Exercises to be Completed 41
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II ampicillin + streptomycin I + II ampicillin + streptomycin Knowing that Strain I carries the gene for streptomycin resistance on the bacterial chromosome and that Strain II carries the gene for ampicillin resistance on a plasmid, list all possible explanations for your observed results. * * * Microbes in the Food Supply Procedure and Results : IMPORTANT! Despite the fact that these organisms were isolated from an 'approved' food source, it's critical to realize that on the agar plates they are now present in extremely high numbers and must be treated as potential pathogens ! 1. Examine the trypticase soy agar plates with the dilutions of alfalfa sprouts. 2.Using the dilution that most nearly results in 30-300 colonies on a plate, calculate the number of organisms per gram of food sample by using: original sample concentration = (# of colonies counted/volume plated) x (1/dilution counted) For example, 38 colonies from the 1:100 sample would be equal to 38 ÷ 0.1 (which equals 380) x [1/10 -2 ]. Remember: [1/10 -2 ] is equal to 1 x 10 2 , resulting in 3.8 x 10 4 bacteria/gram of original sample. 3. Based on the instructions of your lab instructor, calculate the following: MCRO 251 Lab Manual 42
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Organisms per gram of alfalfa sprout 4. Each pair should subculture a single isolated colony of the type selected by your instructor into a TSA broth (to be used later). 5. Record the colony description. 6. Examine any other food plates and share the results with your lab instructor. * * * Testing the Effectiveness of Disinfectants and Antiseptics Introduction Disinfectants are chemicals that are used to kill microorganisms on the surface of inanimate objects. They are not safe for use on tissues. Antiseptics may be used on tissue, such as skin. The concentration of the chemical and the length of contact time are the critical factors that determine the effectiveness of a chemical against a particular microorganism. Bactericidal agents kill microorganisms while bacteriostatic agents inhibit the growth of microorganisms but do not kill them. When a bacteriostatic agent is removed, the microorganisms can resume their growth. Sometimes a disinfectant is bactericidal at one concentration and bacteriostatic at a lower concentration.
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