Q.83 A landfill sample was analyzed by dilution and plating techniques for viable
bacterial count. When one gram of the landfill sample was diluted 1 x 10–4 (w/v) it
yielded 400 CFU. The viable bacterial count (in million, rounded off to the nearest
integer) in one gram landfill sample is _______.
The viable bacterial count in the landfill sample is calculated using standard dilution plating principles, yielding 4 million CFU per gram. This matches the given data and CSIR NET-level microbiology expectations.
Calculation Steps
Start with 1 gram of landfill sample diluted to 1×10-4 (w/v), meaning 1 g in 10,000 mL total volume, so the dilution factor is 104.
The plate shows 400 CFU, representing viable cells from the plated portion (typically 0.1 or 1 mL, but standard formula uses CFU × dilution factor for per-gram count when volume cancels or is normalized).
Thus, viable count = 400×104=4×106 CFU/g, or 4 million (rounded to nearest integer).
Common Pitfalls Explained
No “options” exist as this is a fill-in-the-blank numerical question, but errors include forgetting dilution factor (gives 400, too low) or using 10-4 directly (gives 0.00004, incorrect).
w/v specifies mass/volume, confirming 1 g sample basis for CFU/g. Volume plated is implicit (often 1 mL in such problems, but not needed here).
Plates with 30-300 CFU are ideal; 400 is acceptable for calculation.
Introduction to Viable Bacterial Count in Landfill Samples
Viable bacterial count in landfill samples measures live microbes via dilution plating techniques, essential for environmental microbiology and CSIR NET Life Sciences prep. When 1 gram of landfill sample dilutes to 1×10-4 (w/v) yielding 400 CFU, the viable bacterial count per gram reveals microbial load—key for bioremediation studies. This guide breaks down the CFU calculation step-by-step.
Understanding Dilution Plating Technique
Dilution plating serial-dilutes samples to countable colonies (30-300 CFU/plate ideal).
- 1 g landfill in 104 volume = 104 dilution factor.
- Plate aliquot grows 400 CFU from diluted sample.
- Formula: CFU/g = (colonies counted) × (dilution factor).
Landfill samples suit w/v for soil-like solids.
Detailed Calculation: Landfill Sample 400 CFU at 10-4
- Dilution factor = 104 (from 1×10-4).
- Colonies = 400.
- Viable count = 400×104=4,000,000 CFU/g = 4 million (nearest integer).
| Parameter | Value | Role in Calculation |
|---|---|---|
| Sample mass | 1 g | Basis for CFU/g |
| Dilution | 1 × 10-4 (w/v) | Factor = 104 |
| CFU counted | 400 | Plate observation |
| Final count | 4 × 106 /g | 4 million |
CSIR NET Exam Tips for CFU Questions
Practice avoids errors like ignoring factor or misreading w/v. Relate to biotech applications like waste degradation.
- Verify 30-300 CFU range.
- Round per instructions.
- Units: million CFU/g.
