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Ultraviolet Light: Lethal Effects Exercise 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. Ultraviolet Light: Lethal Effects Exercise 30. Method

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Ultraviolet Light: Lethal Effects Exercise 30

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  1. 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 Ultraviolet Light: Lethal EffectsExercise 30

  2. 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 Lethal Effects of UV: Exercise 30

  3. Antibiotics=chemotherapeutic 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) Antimicrobic Sensitivity Testing

  4. 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) Antimicrobic Sensitivity TestingExercise 33

  5. 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) Antimicrobic Sensitivity Testing

  6. 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

  7. Remove filter Air dry for 1 hour Count metallic colonies Membrane Filter MethodExercise 48

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