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pores of Clostridium tetani, the cause of lockjaw (tetanus), are found in soil and dust—thus, virtually everywhere. Before its cause and pathogenesis were understood, the disease was widespread, often ending in agonizingly painful death. Dr. Shibasaburo Kitasato (1856-1931), working in Robert Koch's laboratory in Germany, was the first to discover how to cultivate C. tetani, and subsequently he made a startling discovery that paved the way for control of the disease. Kitasato was born in a mountainous village in southern Japan in 1856. He was sent by his family to medical schools in Kumamoto and Tokyo. Following his graduation in 1883, Kitasato went to work for the Central Hygienic Bureau in Japan. The Japanese government needed to control epidemics of typhoid, cholera, and blackleg, a clostridial disease of calves, and so in 1885, Kitasato was sent to Germany to study with the famous Dr. Koch.

In Koch's laboratory, Kitasato was given the tetanus problem to study. In the course of his experiments, he discovered that C. tetani would only grow under strictly anaerobic conditions. Once he had isolated the organism in pure culture, he was able to show that it produced tetanus in laboratory animals. He was puzzled, however, by a surprise finding: although the animals died of generalized disease, there was no C. tetani anyplace other than the site where the organism had been injected. By doing experiments in which he injected the tails of mice and then removed the injected tissue at hourly intervals after injection, he showed that the animals only developed tetanus if the organisms were allowed to remain for more than an hour. He further showed that the organisms remained at the site of inoculation; at no time were they found in the rest of the body. Kitasato reasoned that something other than bacterial invasion was causing the disease.

About this time, another investigator, Emil von Behring, was busy investigating how Corynebacterium diphtheriae caused the disease diphtheria. Together, Kitasato and von Behring were able to show that both diseases were caused by poisonous substances, toxins, that were produced by the bacteria. The concept that a bacterial toxin could cause disease in the absence of bacterial invasion was an extremely important advance in the understanding and control of infectious diseases.

Kitasato published his studies in 1890. In 1892, even though urged to stay in Germany, he returned to Japan. The Japanese government was not prepared to support basic research at that time, and so Kitasato established his own institute for infectious diseases where he worked and trained Japanese scientists for the rest of his life. In 1908, Koch paid a visit to Kitasato in Japan and a Shinto shrine was built in Koch's honor. During his later years, Kitasato was instrumental

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Color-enhanced TEM of Staphylococcus aureus in establishing laws regulating health practices in Japan. He died in 1931 at age 75. To honor him, a shrine was erected next to Koch's.

—A Glimpse of History

MOST PEOPLE OCCASIONALLY SUSTAIN WOUNDS that produce breaks in the skin or mucous membranes. Almost always, microorganisms contaminate these wounds from the air, fingers, normal flora, or the object causing the wound. Whether these microorganisms cause disease depends on (1) how virulent they are, (2) how many there are, (3) the status of host defenses, and (4) the nature of the wound, especially whether it contains crushed tissue or foreign material.

Wounds that contain materials such as dirt, leaves, bits of rubber, and cloth usually become infected and do not heal until the foreign material is removed. Often such a wound provides places for microorganisms to multiply and produce injurious substances, out of the reach of phagocytes and other body defenses. Foreign materials may also provide surfaces for biofilms, or the materials reduce available oxygen, thereby impairing phagocytic function and allowing growth of anaerobic pathogens. Clean wounds often heal uneventfully despite microbial colonization,

Nester-Anderson-Roberts: I IV. Infectious Diseases I 27. Wound Infections I I © The McGraw-Hill

Microbiology, A Human Companies, 2003

Perspective, Fourth Edition

692 Chapter 27 Wound Infections but sometimes even a trivial wound can result in a severe, or even fatal, infection by providing an entryway for infection or micro-bial toxins to spread throughout the body.

Wounds can be classified as:

■ Incised, as when produced by a knife or other sharp object, as in surgery

■ Puncture, from penetration of a small sharp object, as when an individual steps on a nail

■ Lacerated, when the tissue is torn

■ Contused, as when caused by a blow that crushes tissue

Burns represent an important category of accidental wounds. In the United States each year, more than 2.5 million people sustain thermal burns severe enough for them to seek medical attention. Of these, more than 100,000 require hospitalization, and 12,000 die from their burns. Burns present special problems. Although initially sterile, thermal burns are often extensive, with a large area of weeping devitalized tissue, representing an enormous and nutritious feast for microorganisms.

Intentional wounds inflicted by surgery represent about 23 million cases annually in the United States. From 1% to 9% of them become infected; the percentages vary according to the type of surgery and the status of the patients' host defenses. Costs related to postoperative wound infections amount to approximately $1.5 billion each year, more than half of the total expense for nosocomial infections. They result in about 13,000 deaths each year. ■ nosocomial infections, p. 499

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