Ultraviolet Light: Lethal Effects Exercise 30

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Ultraviolet Light Lethal EffectsExercise 30

• Germicidal effects of UV due to DNA damage
• UV damaged DNA forms pyrimidine dimers
• Dimers block DNA polymerase transcription
• SOS system DNA repair
• Plastic blocks UV
• Endospore-formers UV resistant
• Bacillus megaterium

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Lethal Effects of UV Exercise 30

• Method
• Swab entire surface of agar with
• S. aureus (non-endospore)
• B. megaterium (endospore)
• Remove lid cover 1/2 of plate with card
• Place under UV light
• Replace lid incubate for 48h at 37?C

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Antimicrobic Sensitivity Testing

• Antibioticschemotherapeutic agents that inhibit
  or kill other microorganisms
• Erythromycin blocks protein synthesis (50S)
• Kills Gram bacteria
• Penicillin inhibits cell wall synthesis
• Kills Gram bacteria
• Gram - bacteria are resistant
• Tetracycline blocks protein synthesis (tRNA)
• Broad spectrum
• Zone of inhibition clear zone no growth
• Affected by
• Diffusibility of agent
• Type of media
• Size of inoculum

• Ampicillin (10 ?g)
• Bacitracin (10 IU)
• Chloramphenicol (30 ?g)
• Kanamycin (30 ?g)
• Streptomycin (10 ?g)
• Triple Sulfa (300 ?g)

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Antimicrobic Sensitivity TestingExercise 33

• Method
• Swab entire surface of agar
• S. aureus (1-4)
• E. coli (5-8)
• P. vulgaris (9-12)
• P. aeruginosa (13-15)
• Allow surface to dry for 3-5 minutes
• Dispense disks tap with forceps
• Incubate for 16-18 hours at 37?C
• Measure zones of inhibition in mm
• Compare to chart (Table VII)

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Antimicrobic Sensitivity Testing

• Ampicillin (75 ?g) targets Gram- bacteria cell
  wall used to treat UTIs
• Bacitracin (10 IU) isolated from Bacillus
  blocks cell wall synthesis in Gram Neosporin
• Chloramphenicol (30 ?g) acts on 50S subunit to
  block protein synthesis broad
  spectrum used for staph causes gray
  syndrome in newborns
• Kanamycin (30 ?g) acts on 30S subunit used to
  treat bone, skin, respiratory, abdominal
  urinary infections
• Streptomycin (10 ?g) acts on 30S subunit to
  block protein synthesis used to treat TB
• Triple Sulfa (300 ?g) inhibits folic acid (used
  to make A, G, T) used to treat vaginitis
• sulfathiazole, sulfabenzamide, sulfacetamide
• E. coli sepsis, diarrhea, UTIs (cephalosporin)
• P. aeruginosa opportunistic lung burn
  infections (ciprofloxicin cephalosporins)
• P. vulgaris enteric bacteria commonly found in
  soil can cause UTIs
• S. aureus skin abscess or toxic shock
  (penicillin)

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Kirby-Bauer Sensitivity Chart

• Ampicillin (10 ?g)
• Bacitracin (10 IU)
• Chloramphenicol (30 ?g)
• Kanamycin (30 ?g)
• Streptomycin (10 ?g)
• Triple Sulfa (300 ?g)

Adapted from Table VII on page 379 of lab manual
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Membrane Filter MethodExercise 48

• Remove filter
• Air dry for 1 hour
• Count metallic colonies