More Meat Based Media

Some microbes grow better in meat type media. We call them proteolytic (protein-splitting) microbes. They are found in decaying meat, intestines, dead animals.

Remember, all measurements are grams per liter of final medium. That is true of every page on this web site. Any liquid medium is called a broth. After we add agar to it, we call it an agar. Example: heart infusion broth + 10 grams of agar => heart infusion agar. Also remember to autoclave every medium for 15 minutes at 15 pounds in cotton stoppered test tubes. Such media may be suitable for weeks or years.

Meat media tend to become more alkaline (pH rises toward 9 or higher) as proteolytic bacteria grow on in it. That is because some bacterial enzymes can cleave ammonia off amino acids. These deaminization enzymes can't do this while the amino acid is in an intact protein or peptide. That may be the reason some bacteria seem to grow better on peptides than when all the free amino acids are supplied in the medium. Deamination of the amino acid alanine is shown below. Notice -ine is the ending for all amino acids.

  H H O-H          H  
  | | |            |
H-C-C-C=O  ====> H-N-H + other products
  | |
  H N-H

Notice the amino group -NH2 group on the alpha carbon. When it is removed the amino group becomes an ammonia molecule. The ability of a bacterium to deaminate phenyalanine is a common assay used in identification of intestinal bacteria. The -COOH group is the carboxyl group. The ability of a bacterium to remove the carboxyl group of arginine, lysine, and ornithine is an important assay in identification of intestinal bacteria.

Biochemists use the suffix -in to designate proteins. Some examples are casein (main protein complex in milk), gelatin (a protein extracted from bones), hemeglobin (binds and transports oxygen inside red blood cells), globin (the protein part of hemoglobin), globulin (any member of a group of proteins insoluble in pure water), pepsin (a enzyme produced in the stomach which in the presence of HCl cuts proteins into proteoses and peptones. Peptones are soluble pieces cut from proteins. Proteoses are soluble fragments cleaved (cut) from proteins by gastric juices (enzymes).

Gelatin is a brittle, nearly transparent, yellowish, odorless, nearly tasteless protein, obtained by boiling in water the ligaments, bones, skin, feet and hooves of mammals, and forming the basis of jellied meats, glue, desserts (Jello), and bacteria media. Since gelatin is a fairly pure and cheap protein, it is useful for testing the abililty of bacteria to digest a particular protein.

There are lots of proteins around the home that you can use use high protein media. Some of those used by professionals are meat, brain, egg, liver, gelatin, can add to TGY and other bases. add agar o gel or use as broth. Skim milk contains the disaccharide lactose and two protein complexes and is a useful medium covered on page b028.

Until I get this page completed, keep in mind you can use a meat grinder to grind any meat, soak the ground meat in water,and then boil it to produce and infusion broth as we did on page b022 to make Easy Broth. You can use such broths, as is, or add other nutrients such as yeast extract, glucose (corn syrup) or other sugar, table salt, etc.

Adding Reagents to Protein Media

Above we learned some bacteria can deaminate one or more amino acids releasing ammonia. Ammonia is basic and raises the pH of the medium. You can detect this pH change by adding a suitable pH indicator. Phenol Red is suitable it is yellow below pH xx and red above ph XX. It is various shades of orange in between. Therefore, if you add phenol red to your meat or milk medium you will find some bacteria turn the medium red. Sometimes the medium is red at the top of the slant and yellow at the bottom. If it is yellow at the bottom the bacterium is fermenting some sugar(s) in the medium and creating acid.

Three amino acids contain sulfur. They are methionine, cystine, and cysteine. Hair has a lot of these amino acids. Can bacteria digest hair? Some bacteria can reduce (add hydrogen to) sulfur to form hydrogen sulfide. Hydrogen sulfide reacts with various metals to form colored precipitates. With cadmium to form Orange or Yellow. With zinc to form white. With iron to form black. You have a choice of adding Ferrous (Fe++) or Ferric (Fe+++). Since ferrous is more soluble, we usually add ferrous sulfate (__gram per liter). If you don't have any of this you could try iron filings. The orange water of a rusty nail is Ferrous; remove the nail and it oxidizes to Ferric. To speed this add a few drops of battery acid.

You might also try adding methylene blue, Ulrich Indicator, or red cabbage juice to your meat media. See the milk media pages for ideas about using these.

Urine as a Medium for Bacteria

Urine is a useful, interesting medium for bacteria. Just collect it, autoclave and use. Analysis of urine is one of the important ways hospital labs check your health. Therefore, working with urine is worthwhile endeavor for the young microbiologist/biochemist. Normal urine is sterile but that is not true for hamburger, milk, and saliva. Urine from diabetic persons may contain up to ___ g of sugar per liter but normal urine is sugar-free. One liter of normal urine contains 50 g solids, 25 g urea, 1 g creatinine, 1 gram of sulfur, and 10 grams of salts mostly NaCl, KCl, and sodium and potassium phosphates. Some day this site will have a page on the composition of normal urine and experiments for studying normal urine.

Due to the urea, urine is a good medium for bacteria that can use urea as carbon and energy source if they can survive the 10 grams of salts. If possible add phenol red and ferrous sulfate to the urine medium. Agar slants might be the best form.

      | |   
   HN=C | 
      | |



Urea is made by the liver. Any creatinine in the diet is excreted without change. Creatinine is found in fish, especially after cooking. Creatinine decreases during starvation, but I have been able determine how or where creatinine is made in the body.

To be continued. Items below will be used for reference during writing.

see page 022 E-broth for methods.

Composition of meat extract


///////////////// notes below will help write this page ///////////

Many Clostridum species will 'storm' milk without use of thioglycolate

General Comments

37oC ... SO4

First installed Feb 1998      Revision #2 1998 Feb 15
Written by Harold Eddleman, Ph. D., President, Indiana Biolab, 14045 Huff St., Palmyra IN 47164
| Indiana Biolab | Home Micro Lab | Bacteria Evironmental Needs | Food Microbiology |

Structure of the 20 Amino Acids

later move to a page introducing the structure of the amino acids. begin that page with the constant part of amino acids.

Cllick here to see the structures. Notice the constant carboxyl and alpha carbon in the Upper Left of each structure. The first letter of the symbol for each aa is located on the carboxyl carbon and the alpha amino group is located just above the last letter of the symbol. Notice the two red hydrogen atoms of the amino group