Popular Science Monthly/Volume 80/April 1912/Ptomaines and Ptomaine Poisoning
|PTOMAINES AND PTOMAINE POISONING|
THE subject of food poisoning is one that is commanding a constantly increasing attention on the part of the general public. A brief resume therefore of the most important facts relating to ptomaines and ptomaine poisoning together with some deductions based thereon may be of interest to all who would be informed on matters relating to their physical welfare—certainly so to those who are practical conservators of the public health.
Ptomaines are chemical compounds of an alkaloidal nature formed in protein substances during the process of putrefaction. In order to a clear understanding of the subject, emphasis is to be laid on the fact that they are purely chemical bodies formed out of the medium in which they occur.
In this respect they are to be differentiated from the toxins, which are poisons of unknown composition, formed within the bacterial cell itself and in the case of certain organisms, given off to the medium in which they grow. They are also to be differentiated from another class of compounds known as leucomaines, which may in some instances be of like chemical composition, but which are formed only within the living body, usually as the result of tissue metamorphosis. From these, when not properly eliminated, we get the varied phases of auto-infection.
Putrefaction is the biochemical process by which all protein matter is reduced to the inorganic state from whence it came, thus completing the life cycle. This change is brought about by the action of microorganisms. A certain group of bacteria have the power to split up the complex protein molecule and thus form new and simpler compounds. As a result of their action we have formed first albumoses and peptones and from these we have formed the amino acids which are the great foundation stones of the proteins. These are still capable of sustaining bacterial life and the splitting-up process continues. As a result we may get a large number of products, solid (crystalline), liquid and gaseous—and among them may be some of the basic compounds which we call ptomaines.
So far about sixty ptomaines have been isolated and studied and of these about one half are more or less poisonous. It is to be borne in mind that the so-called ptomaines are not a distinct class of chemical compounds, but differ widely both in chemical composition and physical characteristics. Indeed it may be said that they have only this in common, that they are basic and contain nitrogen. Some of them are comparatively simple and well-known organic compounds like the simple amines, others are much more rare and complex; "some are strongly alkaline and basic, others but feebly so; some are liquid, oily and volatile, others fixed and crystalline; some are very prone to change, others quite stable."
Two thirds of the known ptomaines contain only carbon, hydrogen and nitrogen. These represent the simple ammonia substitution compounds. All those that contain oxygen in addition (the so-called oxygenated bases) possess the trimethylamin molecule as their basic constituent.
Gautier has probably given the best classification of the ptomaines. He divides them into the following groups:
Monamines of the fatty acid series.
Diamines of the fatty acid series.
Aromatic ptomaines free from oxygen.
Aromatic oxygenated bases.
Unfortunately the isolation of a ptomaine from any decomposed or putrid material is a very difficult matter. This is true largely because of the great number, complexity and diversity of the other substances present in the decomposing mass and the fact that these may be at varying stages of putrefaction.
Some of the ptomaines are volatile and are decomposed at any temperature near that of boiling water. Others, very prone to undergo decomposition, may be destroyed by the action of the reagents used. Hence efforts to determine their presence and character are very apt to be attended with failure. In all of these cases, however, where a sufficient amount of a suspected food can be obtained an attempt should be made to determine the presence of any decomposition products that may have been responsible for toxic symptoms. In every case the chemical analysis must be supplemented by a bacteriological examination (much more promising of results) under both aerobic and anaerobic methods to determine the character of the microorganisms present. From pure cultures thus obtained inoculations should be made in suitable animals to determine their infectious character and filtered cultures used to determine the presence of soluble toxins.
It is quite probable, as the more recent investigations have shown, that many cases of food poisoning ordinarily classed as of ptomaine origin are in reality due to a direct infection by bacteria in the food which possess pathogenic properties or to toxins formed by them. The tendency to designate all bacterial food poisoning as ptomaine poisoning is not therefore strictly in accord with the facts as we now know them.
The resemblance of the ptomaines to the vegetable alkaloids has been noted. These two groups of compounds resemble each other in their chemical composition and to a certain extent in their physiological action. The ptomaines have sometimes been called the animal alkaloids. This, however, is misleading, as ptomianes may be formed in vegetable as well as in animal proteins. Their essential difference is to be found in their origin. The ptomaines are decomposition products and largely belong to the aliphatic series, whilst the true plant alkaloids are cyclic compounds and practically all of them pyridin derivatives. Owing to the wide variation in the chemical constitution of the ptomaines no analytical methods are known or possible by which they can be differentiated as a class from the vegetable alkaloids. This is possible in the case of certain ptomaines but not all. As a result of this it is not difficult to see how serious medico-legal problems may arise. It is believed in not a few instances ptomaines have been mistaken for the vegetable alkaloids in chemico-legal analyses.
For our knowledge concerning the ptomaines we are indebted very largely to the investigations of Selmi, Nencki, Gautier and Brieger. Selmi was the first (1874-77) to suggest the name—ptomaine—and in fact the first to announce their true nature and origin. Nencki was the first (1876) to isolate a ptomaine (collidine) in pure form and determine its chemical formula. Gautier has given the best classification of both the ptomaines and leucomaines. To Brieger, however, belongs the credit of isolating the largest number (nearly one half) of the known ptomaines and of giving us the best methods for their determination. Vaughan and Novy in this country have made some valuable researches along this line. As the result of an investigation of a number of cases of cheese poisoning they succeeded in isolating a substance which when administered to animals produced symptoms quite similar to those caused in the human subject by the poisonous cheese. To this they gave the name tyrotoxicon. This poison or one very similar has also been isolated from ice cream and milk. The chemical composition of tyrotoxicon has not as yet been definitely determined.
In foods like cheese and certain sausages which depend for their flavor on the action of certain microorganisms it is not strange that we should at times have the formation of poisonous compounds. The so-called process of "ripening" as applied to food products is in fact a partial putrefaction in which we have as the result of bacterial action the formation of ammonia compounds and amino acids which render the food more palatable. It is therefore not a matter of surprise that we should have at times a condition of "over-ripening" with the formation of chemical compounds of a poisonous character. It is to be borne in mind that ptomaines are not found only as the result of advanced putrefaction. Bather are they the products of the earlier stages of protein decomposition. In advanced putrefaction they may themselves be broken down into more simple compounds. Thus Brieger isolated from a putrid mixture a ptomaine (peptotoxin) which he was unable to find when the putrefaction was more advanced.
The symptoms of ptomaine poisoning vary in kind and severity, depending on the nature and quantity of the poison consumed. These may be wholly or in part referable to the gastro-intestinal system. As a result we may have vomiting, abdominal pain, diarrhea or constipation, usually attended with great prostration. In a majority of the cases there is evidence of involvement of the central nervous system and in some cases the symptoms are wholly of a nervous character. Prominent among these are disturbances of vision and dryness of the mouth and throat. There may be fever or a subnormal temperature. Very often there is great weakness, rapid pulse and a tendency to collapse. Other symptoms which may or may not be present are vertigo, dyspnoea, convulsions, delirium and various skin eruptions. In some cases the symptoms simulate very closely poisoning by one of the vegetable alkaloids.
There is little room to doubt that many cases of acute illness are the direct result of some form of bacterial poison consumed with the food but which in isolated cases are not always recognized as such and often called by other names. It might be said that this factor in causing sickness finds but scant recognition save in those instances where a number of persons in a community are similarly stricken at the same time.
The prophylaxis of ptomaine poisoning resolves itself into the prevention as far as possible of the bacterial invasion and decomposition of our foods and food products. Certain foods like chopped meats, cooked potato and milk and the milk products lend themselves most readily to the growth of microorganisms and for this reason are to be the more carefully guarded.
Canned goods, especially the canned meats, are frequently the source of ptomaine poisoning. This results from the fact that they are not always perfectly sterilized before sealing, and, being often held in storage for a long time, an excellent opportunity is afforded for the formation of putrefactive poisons. Canned goods should in no case be consumed if there is any evidence of gas formation as shown by "blown" cans or the escape of gas on opening the can or, if there is any rancidity or putridity of the contents.
Fish, oysters and other sea foods undergo putrefactive changes very speedily and in so doing are very prone to form poisonous products. Several of the ptomaines were first isolated from the decomposed flesh of fish. Mitilotoxin (possibly a leucomaine), the most powerful of this class of poisons, was first obtained from mussels.
Great care should be taken to avoid eating fish or any of the sea foods which show the slightest evidences of putrefaction.
Heat of sufficiently high degree is destructive to all bacteria and is largely depended upon to render harmless any disease-producing germs that may be contained in our food. While this is true of bacteria it is not true of all the products formed by them. Certain ptomaines and toxins may be destroyed by heat. Others are not susceptible to its influence. Therefore heat as employed in the process of cooking can not be regarded as a safeguard against ptomaine poisoning. Moreover it is often after cooking that these poisons are formed. Many of our cooked foods constitute the very best kind of culture media and as a result putrefactive changes may take place in them very rapidly. The safe plan is therefore to eat food soon after cooking or if it is reserved for any length of time it should be well protected from bacterial invasion and kept at a low temperature.
Cleanliness and low temperature afford the best means at our command for preserving foods from bacterial action—cleanliness to prevent the presence and contaminating influence of the millions of bacteria, often of the putrefactive type, which are always to be found where dirt and filth of any kind is allowed to accumulate and where flies and other insects are given free access, and low temperature to prevent the multiplication of those already in the food, no matter how careful we may have been to exclude them. Cold, even a freezing temperature, is not fatal to bacteria, but it does decidedly retard their growth. Even at the temperature of the ordinary refrigerator (about 10° C. or 40° F.) we find that most organisms multiply very slowly and as a result putrefactive changes are much retarded. Refrigeration is therefore a necessity for the proper keeping of foods, at least during the hot season. But to be efficient the refrigerator must be properly managed. Unless it be kept clean, properly ventilated and well supplied with ice it is practically useless, in fact absolutely dangerous.
Public sentiment is now demanding that those who produce and handle our foods should furnish them to us in a pure and wholesome condition and sanitary officials on every hand are endeavoring to enforce the proper regulation and protection of our food supply. This effort is most commendable. It is well to remember, however, that official regulation can extend only to our doors and to be fully effective it must be supplemented by proper management in our homes and in all places where food is consumed.
In conclusion, we must admit that well-defined cases of ptomaine poisoning are comparatively of rare occurrence when we consider the amount of food consumed and the number of consumers. They would indeed be exceedingly rare if those who are charged with the preparation and handling of our foods would always exercise the proper precautions along the lines we have indicated.