Lecture 25
Environmental and Food Microbiology I

I. Continue Lab #24

A. Water Microbiology (MTFM)



B. Soil Microbiology

1. Isolation of Different Types of Soil Microorganisms

a. Count the colonies on the plates used to select for growth of molds, Streptomyces species and other bacteria.
Only plates containing between what two numbers of colonies should be counted?? ____________________________________________________

b. Calculate the # of organisms per gram of soil:

Does the number recorded above represent the actual concentration of microorganisms in soil? ___________________________________________ ________________________________________________________________

2. Isolation of Nitrogen Fixing Bacteria

a. A nitrogen-free medium ______________________ contain an inorganic source of nitrogen. Therefore, organisms that can live on this medium must be able to utilize __________________________________.
b. Take a heavy inoculum of the nitrogen-free broth and _________________________________________.
c. The major genus represented on this plate will be _________________________.

1.) Azotobacter are nitrogen fixers that are found in most _____________________________ ____________________________________.
2.) They are large, _________________________ ___________________ that have the ability to form resting structures called _____________.
II. Food Microbiology
Microbes in food are important for several reasons:

A. Food ________________________.


1. Species of _____________________, Erwinia and many of the lactic acid bacteria are common spoilage bacteria.
2. While spoilage bacteria lead to distasteful, smelly food, they are generally _______________________. However, a large number of spoilage microorganisms can indicate the presence of a ___________ ___________________________________.

B. Foodborne ______________

We will test E. coli, S. aureus and P. aeruginosa for their susceptibility to a variety of natural antimicrobials found in food.

C. Food production- __________________________________

1. The starter culture of Cheddar cheese is a mixture of _____________________ spp.. The starter culture of ______________________ is a mixture of Streptococcus thermophilis and Lactobacillus bulgaricus.
2. _____________________ species are also used to make sour cream and yogurt.
3. Acetobacter is used in the production of ____________.

D. Food ___________________

1. Lactobacillus-produces ________________________ which is often used as a food preservative.
2. The lactic acid bacteria (LAB) produce small antimicrobial peptides called ______________________. These bacteriocins help the LAB compete in the food medium on which they grow. Some of the bacteriocins are being used commercially to help preserve food.

E. Antimicrobial substances that are found naturally in food:


We will test E. coli for its susceptibility to a variety of natural antimicrobials found in food.
F. Caries Susceptibility test
This test correlates the ___________________________ present in the saliva to an individual’s susceptibility to ____________________.

Rachel Watson, M.S.
AG 5010
766-3524
Cell: 307-314-9636
rwatson@uwyo.edu