BIOLOGY Volume 2 - A Guide to General Biology - 2004

15. HEALTH AND DISEASE

15.4. Disinfectants, Sterilization, and Antisepsis

Microorganisms are ubiquitous. Some of them colonize the Skin of humans and animals, while others live inside the body; both types are capable of causing disease. The fight against these pathogenic microbes began only in the last century, immediately after Louis Pasteur proved their existence. Prior to that, most surgical Procedures had rather grim outcomes: at best, recovery was prolonged and accompanied by fever, while at the worst, the patient died from tetanus, septicemia (Blood poisoning), or gangrene. The deeper the surgeon penetrated into the patient's body, the higher the risk of wound infection. Thanks to Pasteur's experiments, physicians learned that microorganisms (germs) could be eliminated by various Methods, such as heating, chemical Treatment, or filtration.

Joseph Lister, a professor of surgery at the University of Glasgow, heavily influenced by Pasteur's work, began searching for chemical agents that kill microorganisms in 1860. Carbolic acid (phenol) was chosen for the first experiments. Lister used it to treat surgical instruments, catgut (thread for suturing wounds), ligatures (threads for tying off Blood Vessels), and the physician's hands—essentially everything that would come into contact with the Tissues being operated on (Fig. 15.13). In addition, carbolic acid was used to wash the patient's skin at the site of the future incision, as well as the operating room floor. This method led to a decrease in the number of postoperative infections. With its help, pathogens are destroyed before they can penetrate The Human Body.

Carbolic acid is a classic example of an antiseptic (see below). The Use of such substances made it possible to perform surgeries in sterile (germ-free) conditions, using sterile instruments, sterile suture Materials, etc.

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Fig. 15.13. Surgery in Lister's time. The man on the right is holding a carbolic acid sprayer, first introduced by Lister.

15.4.1. Antiseptics and Disinfectants

Antiseptics and disinfectants are substances used to destroy pathogenic microorganisms.

The distinction between antiseptics and disinfectants is conventional: the former are relatively harmless to humans and are used for direct application to the body, whereas the latter are more aggressive and used for decontaminating rooms, equipment (sinks, tables, bathtubs, dishware, instruments, etc.), and technical systems (sewage systems, ventilation, etc.).

Treatments are usually carried out using liquid preparations. Their effectiveness depends on Temperature, concentration, and exposure (contact) time.

Microbial resistance to a given antiseptic (disinfectant) varies greatly. For example, the poliovirus and the tuberculosis bacterium are highly resistant. Spore-forming Bacteria and Fungi are able to survive extreme environmental conditions in the form of spores, so it is hardly surprising that many cold chemicals have little effect on them.

By their nature, antiseptics and disinfectants are quite diverse. Here are a few Examples.

1. Hypochlorites, such as calcium and sodium hypochlorites, combine with Water to form hypochlorous acid and oxygen. This acid rapidly kills microbes. Various commercial preparations of these substances are available under different names, such as Domestos and Milton.

2. Phenol (carbolic acid) is one of the earliest antiseptics/disinfectants, introduced into practice by Lister himself, though it is rarely used today. Phenol derivatives combined with Surfactants (detergents) are used for hospital disinfection.

3. Alcohols, such as ethanol and isopropanol, are frequently used as antiseptics and sometimes as disinfectants (for instance, for storing boiled syringes). A 70% alcohol solution kills tuberculosis bacteria and certain Viruses, yet it is completely ineffective against fungal and bacterial spores. Alcohol vapors are highly flammable and therefore pose a fire hazard. Furthermore, these substances are relatively expensive.

4. Aldehydes, especially formaldehyde (in solution as formalin), are used for surface decontamination, but they are strong irritants to the skin and respiratory tract. The ability of formaldehyde to kill putrefactive bacteria explains the widespread use of formalin for preserving dead animal tissues, although it is now being replaced by substances less harmful to humans.

5. Surfactants enhance the wettability of surfaces and, consequently, their contact with the dissolved disinfectant/antiseptic. In addition, surfactants remove grease, and along with it, contaminants, including microbes. Surfactants are usually applied prior to the actual disinfection treatment (или in combination with it).

6. Chloroxylenol (e.g., in the form of Dettol) and iodine are used as disinfectants, and in more dilute solutions, as antiseptics.

Some widely used antiseptics are presented in Table 15.10.

Table 15.10. Antiseptics and their Applications