BIOLOGY 216 - Bacterial Enumeration-Dilutions and Plate Counts

Bacterial Enumeration-Dilutions and Plate Counts

Hands-On Labs, Inc.
Version 42-0306-00-01

Lab Report Assistant

This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Exercise 1: Dilutions and Viable Plate Counts

Data Table 1.Dilution Plate Counts

Dilution	Photo	Count and Viability (Viable, TFTC, or TNTC)
10-1
10-2
10-3
10-4
10-5
10-6

Table 2.Calculations of Original Sample CFU/mL.

Calculation	Answer
Dilution Plate CFUs
Dilution Factor of Viable Plate
Volume of Diluent added to Plate
CFU/mL of Original Sample: CFU/(Volume x Dilution Factor)

Questions

A. What is a colony forming unit and how is it used to infer microbial numbers in a sample?

B. Why are plate counts of 30-300 considered viable?

C. If you allowed your dilution tubes to incubate for 24 hours before plating them, do you think the results of the experiment would be impacted? Assume that unlimited resources are present in the tubes. Explain your answer.