Define serial dilution.
Stepwise dilution to reduce concentration.
What makes blood agar differential? Define alpha, beta, gamma hemolysis.
RBC hemolysis patterns. Alpha = green Beta = clear Gamma = none
O/F test: sealed tube no change, unsealed yellow at top?
Organism is oxidative (uses oxygen to metabolize glucose).
How detect carbohydrate fermentation with phenol red?
Yellow = acid production; bubble in Durham tube = gas.
What test detects acetoin production?
Voges-Proskauer (VP) test.
Growing bacteria vs viruses?
Bacteria grow on agar → counted by CFU Viruses require host cells → counted by plaque assay
Why use control tube in decarboxylase test?
Ensures color change is due to amino acid metabolism, not base medium.
Simmons citrate indicator, pH change, enzyme?
Bromothymol blue. Blue = alkaline. Enzyme = citrate permease.
Green negative (and start color)
Blue positive
What is coagulase? Positive result? Exoenzyme vs endoenzyme?
Enzyme that clots plasma. Positive = clot formation.
Exoenzyme = secreted outside cell. Endoenzyme = works inside cell.
What is antibody isotype?
Antibody class (IgG, IgM, IgA, etc.).
What is serology?
Study of antigen-antibody reactions.
Brownian vs true motility?
Brownian = random vibration. True motility = directional movement.
Flagellar arrangements?
Monotrichous = one. Lophotrichous = tuft. Amphitrichous = both ends. Peritrichous = all over.
Innate vs adaptive vs cell-mediated immunity?
Innate = non-specific defense. Adaptive = specific response. Cell-mediated = T cells destroy infected cells.
H2S production in TSI/SIM shows what?
Black precipitate (iron sulfide).
H2S produced from what compounds?
Sulfur-containing amino acids.
Cysteine and methionine
Indole is produced from which amino acid?
Tryptophan.
Urea agar indicator, enzyme, pH change?
Phenol red. Enzyme = urease. Ammonia T pH → pink.
What do bacteria use nitrate for?
Alternative electron acceptor (anaerobic respiration).
Nitrate reduction enzymes & products?
Nitrate reductase → nitrite Nitrite reductase → nitrogen gas
Effect of zinc in nitrate test?
Turns red if nitrate still present (true negative).
How detect gas in broth?
Bubble in Durham tube.
What are antimicrobial agents?
Substances that kill or inhibit microbes.
Zone of inhibition? MIC?
Zone = clear area around antibiotic disk
MIC = lowest concentration that inhibits growth
Minimum Inhibitory Concentration
