An original sample of water containing 4.20 X 109 CFU/mL was diluted by 4 successive 1/100 dilutions. Exactly 1 mL from the last dilution was used to prepare a pour plate. After incubation, how many colonies were present on this plate?

What is the amount (mL) of pre-culture (108 cell/mL) necessary to inoculate (to add) in a 2-liter culture media for a concentratio 6.5 x 106 cells/mL?

What is the likely result if you try to use the 100X objective without immersion oil?

A tampered sack of powdered milk was analyzed by getting 50 grams of composited sample and diluting it with 450 ml of sterile distilled water. One ml and 0.1 ml of sample suspension were inoculated in 50 ml Dextrose Tryptone Bromcresol Purple agar and were heated at 100˚C for 5 minutes. Each flask was poured into 3 plates. After the incubation, opaque colonies surrounded by a yellow halo in purple field were counted. The following counts were obtained from the plates: 95, 107, 92, 26, 28 and 27. Compute for the total spore counts and express your final answer per 50 grams of the powdered milk sample.