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Labs 7 and 8 Manual

Labs 7 and 8 Manual - WEEK 7 October 11 17 Control of...

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WEEK 7: October 11 - 17 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  succes sful  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 II ampicillin + streptomycin I + II ampicillin + streptomycin MCRO  251  Lab  Manual Exercises to be Completed   43
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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. * * * Microbial Flora of the Throat Materials (per  pair of students) 2 sheep  blood  agar  plates Procedure 1. After  consulting  with your  lab  instructor,  select  an  isolated  colony,  and  streak  for isolated   colonies  on  the  sheep  blood  agar  plate,  heating  your  loop  between  quadrants. 2.   Rubber   band   your   two   plates   together   and   place   inverted   into   the   labeled   box   for   incubation. * * * Microbes in the Food Supply Procedure and Results : IMPORTANT!   Despite  the  fact that these  organisms  were  isolated  from  an  'approved'  food  source,  it'   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) MCRO  251  Lab  Manual 44
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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 bacteria/gram of  original sample.  3. Based on the instructions of your lab instructor, calculate the following: Organisms per gram of alfalfa sprout 4. Each pair should subculture a single, well-isolated colony of the type selected by your instructor into a trypticase  soy broth (to be used later in this lab session).
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