Destruction of microbes. Part 1


Microbes can be killed by various physical influences, such as extreme temperatures. But there are other effective ways.

Therefore, it is always a good idea to heat food that has been stored for a long time, and the temperature should be high enough to destroy microorganisms, i.e. above 70 C. Ultraviolet radiation also kills germs, so does gamma radiation, and probably processing food with these types of electromagnetic radiation is the best way to preserve food. Unfortunately, this method is rarely used, which is associated with the vigorous activity of opponents of this method of sterilization. Opponents play on the incompetence of the general public, who believe that food subjected to radioactive processing can be radioactive.

While these modern methods are popular only among those who understand the situation, the rest of the population destroys microbes with the help of chemicals. Now the arsenal of antimicrobial weapons is quite diverse, these include: strong oxidizing agents such as bleach, hydrogen peroxide and ozone; chlorophenols such as triclosan; and lesser known quaternary ammonium salts such as cetrimide. These substances work through different mechanisms: oxidizing agents affect the molecular structures of microbes; chlorophenols are able to diffuse through the cell membrane and block the metabolism of microbial cells; Quaternary ammonium salts destroy the cell membrane.

Apparently, oxidizing agents are the most effective, they affect not only the cell membrane, but also proteins and all other molecules that have N-H and S-H bonds in their composition, and such bonds are often necessary for the functioning of enzymes. . Chlorophenols also attack cell membranes and enzymes, and when a large number of these molecules enter the inside of a bacterial cell, this can lead to the transition of the intracellular fluid into a gel-like form. Quaternary ammonium salts attach to the bacterial cell wall and form holes in it, causing the cell to die.

Antimicrobial substances have a lot of advantages, but along with them there are serious disadvantages, indicated in the table below. The table also mentions alcohol (ethanol) — another substance with antimicrobial activity, it is used for washing the mouth, although not in the concentration shown in the table. Alcohol is able to dissolve bacterial membranes and denature proteins, for antiseptic purposes. It is most effective to use 70% alcohol. Although to a lesser extent, but at 50% concentration, alcohol is also active, which means that in emergency situations, vodka or gin can be used as an antiseptic.

If we eat food on which pathogenic bacteria have had enough time to despoil, within a few days we will have to pay for our mistake.

Table. Antiseptics, advantages and disadvantages

Substance Advantages Flaws
Bleaching powder

Kills all germs

Long shelf life

Strong chlorine smell

Becomes dangerous when mixed with other acid cleaners

Environmental pollution

Hydrogen peroxide

Kills most germs

Not harmful to the environment

Short shelf life

Degraded by many enzymes

Ozone Kills all germs

The effect is short-lived

The impossibility of mass use


kill bacteria

Long lasting effect

Environmental pollution

Ineffective against viruses and fungi

Alcohol (70% solution)

Kills most germs

High stability

fire hazard


In the United Kingdom, there are about 85,000 food poisonings each year that require medical attention. This means that the incidence is fifteen people per thousand. Of course, in most people the poisoning is relatively mild and manifests itself only in vomiting and diarrhea, symptoms that are experienced by about twenty times more victims of food poisoning who do not find it necessary to see a doctor. And studies conducted in the early 1990s in the Netherlands indicate that we are largely underestimating the problem of food poisoning. While only a few hundred cases of gastroenteritis a year are recorded in this country, famous for its cleanliness, scientists have suggested that this number may actually exceed two million, their opinion is based on the fact that, according to statistics, only one person in a thousand with vomiting and diarrhea consult a doctor.

A foodborne infection may require hospitalization and can sometimes be fatal, especially when it affects the youngest and weakest. The bacterium E. coli O157 causes poisoning due to its toxin, which leads to bleeding of the intestines and even to impaired kidney function. This bacterium can have a long incubation period of up to two weeks, and only 100 microbes are enough to cause disease. E. coli O157 lives in the intestines of cows, so we rarely come into contact with it, but if raw beef turns out to be infected with this microorganism and subsequently does not undergo the necessary cooking, the microbe can be introduced into the human body. Undercooked steaks and hamburgers, unpasteurized milk are the main sources of infection, but children can pick up the infection just by playing with animals or collecting sheep excrement. Fortunately, cases of such infection are quite rare, as in the United Kingdom they are recorded less than a thousand a year. The most common causative agents of food poisoning are Salmonella and Campylobacter, which can infect poultry meat, raw eggs and dairy products, and the infection can enter the human body through the use of these products, both at home and in catering establishments.

One important source of pathogens is a damp kitchen tablecloth, which can harbor billions of bacteria. While most microbes are relatively harmless, when, say, chicken blood gets on a tablecloth, you should either dispose of the tablecloth or rinse it in bleach to be safe.


Some people worry that the overuse of disinfectants will eventually lead to the emergence of a resistant microorganism that could turn out to be an even more terrible killer than those that exist today. The validity of these fears is debatable. Indeed, when conducting antibiotic therapy, doctors often encounter a situation where a pathogenic strain of a microorganism appears that is resistant to the action of antibacterial drugs. But a distinctive feature of antibiotics is their high selectivity, that is, the ability to destroy bacteria without affecting the cells of the host organism. In order to achieve such selectivity, it is necessary to limit the targets of antibiotic action, often reducing them to a single enzyme. In this regard, pathogens manage to adapt to antibiotics by modifying one or two of their proteins. Another thing is disinfectants that act like an explosive fan, scattering their fragments that hit several vulnerable points of the enemy at once. At the same time, enzymes, RNA, membrane molecules, molecular messengers are simultaneously affected. In addition, this impact is so rapid and so deadly that there is little chance for microbes to develop a multiple defense strategy.

Source: based on the book by John Emsley «On the benefits and harms of the products we love to buy»

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