Microbiology Lab Practical 3 QUESTIONS AND ANSWERS 100%
ACCURATE 2025.
Zone of Inhibition - ✅✅if chemotherapeutic agent kills the test organism, a zone
around disk forms with no growth
Larger ZOI - ✅✅size of the zone of inhibition that shows a more prevalent antibiotic
Gram + bacteria - ✅✅gram +/- bacteria is more effective against an antibiotic
because of the thick all of peptidoglycan
Antimicrobics - ✅✅Streptomycin, Erythromycin, Tetracycline, Penicillin
Streptomycin - ✅✅crosses cell wall through passive diffusion, crossing gram (-) cell
wall better
Erythromycin, Tetracycline - ✅✅inhibits protein synthesis, more effective against
gram (+)
Penicillin - ✅✅disrupts peptidogylan cross linking process, more effective against
gram (+)
yellow - ✅✅color phenol red turns when acidic, means the unknown ferments lactose
resulting in acid production
Tests to Identify Unknown - ✅✅SIM medium, thioglycolate medium, API 20E system
SIM - ✅✅Hydrogen sulfide production, indole production, motility
H2S test enzyme - ✅✅cysteine desulfurase
H2S positive test - ✅✅black precipitate
Indole test reagent - ✅✅Kovac's reagent
Indole test enzyme - ✅✅tryptophanase
Indole positive test - ✅✅red ring along top
ACCURATE 2025.
Zone of Inhibition - ✅✅if chemotherapeutic agent kills the test organism, a zone
around disk forms with no growth
Larger ZOI - ✅✅size of the zone of inhibition that shows a more prevalent antibiotic
Gram + bacteria - ✅✅gram +/- bacteria is more effective against an antibiotic
because of the thick all of peptidoglycan
Antimicrobics - ✅✅Streptomycin, Erythromycin, Tetracycline, Penicillin
Streptomycin - ✅✅crosses cell wall through passive diffusion, crossing gram (-) cell
wall better
Erythromycin, Tetracycline - ✅✅inhibits protein synthesis, more effective against
gram (+)
Penicillin - ✅✅disrupts peptidogylan cross linking process, more effective against
gram (+)
yellow - ✅✅color phenol red turns when acidic, means the unknown ferments lactose
resulting in acid production
Tests to Identify Unknown - ✅✅SIM medium, thioglycolate medium, API 20E system
SIM - ✅✅Hydrogen sulfide production, indole production, motility
H2S test enzyme - ✅✅cysteine desulfurase
H2S positive test - ✅✅black precipitate
Indole test reagent - ✅✅Kovac's reagent
Indole test enzyme - ✅✅tryptophanase
Indole positive test - ✅✅red ring along top
