222 PROTEIN (NITROGEN) METABOLISM OF BACTERIA 



products. Indol and skatol result from the action of bacteria on tryptophane, and the 

 phenol has its origin largely in the tyrosine liberated from the protein molecule. 



Hydrogen sulphide also is a common product of bacterial action on protein and 

 sulphur-containing derivatives of protein, and mercaptans (methyl and ethyl sul- 

 phide) are liberated in the process of anaerobic decomposition by the putrefactive 

 anaerobes. They are derived apparently from the cystin which forms a part of the 

 molecule of most proteins. 



The amino acids themselves are physiologically inert. Before they can be of any 

 use to the bacterial cell they require further disruption or rearrangement of the ele- 

 ments, and this is readily accomplished by bacteria, through enzymes and catalysts, 

 presumably within the cell itself. This transformation of the amino acids is one of 

 deaminization in which free ammonia is formed as such out of the amino (NH,) 

 groups. This process is commonly one of hydrolysis, with the formation of oxy acid, 

 as is shown in the following simple equation: 



CH. • NH. • COOH+HOH = NH3+ CH.OH • COOH 

 Glycocoll Oxyacetic acid 



Other processes of amino acid change and ammonia liberation are those of reduc- 

 tion, oxidation, oxidation and reduction, and decarboxylation, with the formation, 

 besides ammonia, of amines (R-NH2), alcohols, lower fatty acids, and CO2, as the 

 case may be. 



In this transformation of amino acids by bacteria, products are at times con- 

 structed which are toxic to the animal organism. By a process of decarboxylation, 

 toxic amines and diamines may be produced, as, for example, tyramine (from tyro- 

 sine), histamine (from histidine), and agmatine (from arginine). Other so-called 

 ptomaines are neurin and methyl guanidine. However, not so much credence is given 

 today to the idea of "ptomaine poisoning" as was done several years ago, and bacterial 

 poisons are now generally regarded as the toxic products of specific organisms, like 5ad. 

 enteritidis and CI. hotulinum. 



Ultimate products of bacterial protein decomposition, if the process is not inter- 

 rupted, are of the simplest character, and may include ammonia, nitrous oxide, nitrate, 

 nitrogen, hydrogen sulphide, methane, carbon dioxide, hydrogen, and water. The 

 nature of the final products depends, of course, on the amount of available atmospheric 

 oxygen. 



The term "putrefaction" has acquired two distinct meanings. In the more general 

 usage it signifies decomposition of protein material through bacterial action, as against 

 "fermentation" or decomposition of carbohydrates, with or without the formation 

 of gas. It has been used by Bienstock' and by Rettger^ in a more restricted sense to 

 mean anaerobic decomposition of protein with the production of foul-smelling prod- 

 ucts which are characteristic of cadaveric decomposition. 



The same observers have maintained that, while many aerobic and facultative 

 anaerobic organisms have the ability to decompose protein, they do so only under 

 aerobic conditions, and that real putrefaction is the work of obligate anaerobes. This 



' Bienstock,: Arch./. Hyg., 36, 335. 1899. ^ Rettger, L. F.: /. Biol. Chem., 4, 45. 1908. 



