Lab 9: Chemical control of microbial growth

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Lab 9 Chemical control of microbial growth
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Disinfectant

• Chemical used on surfaces of inanimate object to
  kill microbes
• Chlorine swimming pool
• Chloramine drinking water
• Alcohol lab bench, hospital. This is more
  effective if mixed with water (70 more effective
  than 95)
• Ozone, potassium permanganate, quaternary
  ammonium, sodium hypochlorite (bleach)

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Antiseptics

• Chemical used on living tissues to kill microbes
• Alcohol
• Iodine
• Hydrogen peroxide
• Some disinfectants are also antiseptics
• In surgery prefer to use aseptic (sterile)
  techniques instead of antiseptics

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Antibiotics

• Drugs that kill or inhibit the growth of some
  bacteria
• Bactericide (kill)
• Bacteriostatic (Inhibit growth)
• Target microbes with minimal side effects to the
  host
• Will also kill friendly host bacteria (such as
  the ones in digestive tract)

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Antibiotic

• Produced by mold
• Produced by other bacteria
• Can also be produced in laboratory
  chemotherapeutic agent ? purely synthetic

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Objective 1 Effectiveness of Antibiotics
(Individual) Disk-diffusion technique

• Swab the entire surface of 1 MH (Mueller-Hinton)
  plate with 1 bacterial culture

• Staphylococcus aureus, Pseudomonas aeruginosa,
  Bacillus subtilis, or Escherichia coli Place 3
  paper disks containing antibiotics onto the MH
  plate. you use 3 different antibiotic per plate,
  3 disk total per plate
• Let the plate dry for a 5 minutes. So the disks
  adsorb to the agar. ? invert
• Incubate at 37C.

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Objective Effectiveness of Antibiotics
http//www.srga.org/BILDER/Inok2.gif
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Forcep sterilization

• Put into alcohol
• Flame ? let cool
• Use
• Put back into alcohol
• Flame
• ? your done
• Do not put hot forceps into the alcohol

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Zone of inhibition

• resistant

intermediate
susceptible
http//dept.kent.edu/microbiology/htm/resist.jpg
http//www.bspp.org.uk/bsppnews/bsppnews38/byron.j
pg
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Zone of inhibition (mm)
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Objective 2 II. Effectiveness of Antiseptics
Disinfectants

• Using sterile forceps place 1 sterile paper disks
  into plates containing antiseptics/ desinfectants
• Repeat this step using other antiseptics/
  desinfectants
• Using a cotton swab on 1 TSA plate, make a lawn
  with 1 of the four organisms
• Bacillus subtilis,
• Staphylococcus aureus,
• Pseudomonas aeruginosa or
• Escherichia coli
• Using a sterile forceps place the 3 disk made
  during step 1 onto the plate.
• You may lightly press the disk into the agar. Be
  careful to not press the disk below the agar
  surface.
• Label the plate and incubate it in the inverted
  position at 37C until the next lab period

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Objective 3. Effectiveness of washing hands

• 1 TSA plate divided into fourth
• In each section touch after a hand washing action
• quadrant 1 dry touch prior to any hand washing
• quadrant 2. wet touch after washing hands with
  only water
• quadrant 3. wet touch after washing hands with
  soap and water
• quadrant 4. dry touch after washing hands with
  soap and water again
• Let plate dry before turning it upside down
• Incubate at 37