Gram-Positive Cocci

BACTERIAL TAXONOMY (AN OVERVIEW)

The classic approach to the classification of bacteria is based on size and shape, later aided by reaction to Gram stain. As advances in microscope-making were made and simple biochemical tests became available, gradually the system became more refined. The science of taxonomy matured with the availability of the electron microscope and advances in molecular biology. Muller may have been the first biologist to attempt to classify bacteria in late 18th century, but his attempts were limited by lack of understanding of bacteria and crudeness of microscopes. Cohn, in late 19th century, made further advances, but serious attempts to classify bacteria were first made only in 20th century. Bergey’s Manual of Determinative Bacteriol- ogy was first published in 1923 and it instantly became the foundation of and the most authoritative source for bacterial taxonomy. Aided by inputs from the American Society for Microbiology, international societies for bacterial taxonomy and nomen- clature, and the International Journal of Systemic Bacteriology, Bergey’s manual has been greatly refined and its scope enlarged. Its 9th edition was published in 1994. Another remarkable contribution to bacterial taxonomy was made by the publication of Bergey’s Manual of Systematic Bacteriology, a five-volume set that examines bacterial taxonomy in greater detail. Students interested in bacterial taxonomy are encouraged to consult these highly authoritative sources.

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Antiseptics and Disinfectants

The terms “antiseptic” and “disinfectant” are often confused and misused in micro- biology and medicine. Typically, “antiseptic” refers to an agent used to minimize, destroy, or remove microbial population on a living surface, such as the skin of a person who needs to be prepared for injection or a surgical procedure. A disinfectant, on the other hand, is a substance used to eliminate or minimize microbial presence on an inanimate surface, such as a work bench, glassware, or surgical instruments. It is noteworthy that both antiseptics and disinfectants can either be a microbicide or a microbistatic. In this chapter, we will treat the two entities together under the banner of control of microbial population. The microbial population in or on a surface, material, or product can be controlled, minimized, or eradicated either by physical means or by chemical means, some of which are summarized below.

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Antibiotics and Other Chemotherapeutic Agents

Technically, the antibiotic era began with the discovery of penicillin by Sir Alexan- der Fleming in 1929. However, its development could occur only during World War II. By that time, an energetic soil scientist, Dr. Selman Waksman, had established a school of soil microbiology in New Jersey’s Rutgers University. Focusing on soil- borne aerobic actinomycetes, his group started a systematic program that lead to the discovery of streptomycin, an antibiotic credited with saving lives of millions of tuberculosis patients all over the world. Since then, his group at Rutgers as well as his students in various educational and industrial research laboratories went on to discover thousands of antibiotics, which include almost all the powerful drugs, such as tetracycline, erythromycin, chloramphenicol, amphotericin B, and vancomycin. Traditionally, the term “antibiotics” has been used for the antimicrobial agents derived from microorganisms. Since a number of antibiotics currently in use are actually synthetic, the term antibiotics has become synonymous with antimicrobial agents used for the treatment of infectious diseases.

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Host-Microbe Interactions

The human body reacts in many different ways to microorganisms. These interac- tions can be summarized in the following categories:

RESIDENT MICROBIOTA

All surfaces of the human body, including the skin as well as the mucous membranes that surround the inner parts of the mouth, nostrils, genitals, and gastrointestinal tract, are inhabited by a distinct set of microbial communities, which are specifically adapted to the local physical and chemical environment. Such normal microorgan- isms, called resident microbiota, perform extremely important roles.

1. Resident microbiota engage all available binding sites on the host cell sur- faces, thus invaders have a diminished possibility of attaching to the host cell surfaces.

2. Many microbes secrete vitamins that are absorbed by the host and serve important nutritional needs.

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TRANSMISSION OF INFECTIOUS DISEASE (MODE OF DISSEMINATION)

Airborne (Inhalation of Bioaerosols) 

A bioaerosol contains bacteria in its center, surrounded by air and a small amount of liquid, generally saliva. Bioaerosols may be produced due to sneezing, coughing, or talking. Depending on the force of sneezing or coughing, the bioaerosol-borne microorganism can travel up to several meters in air. Almost all respiratory tract infections are airborne; some can also pass from person to person through the inhala- tion of bioaerosols. Some of the examples of airborne infections include tuberculo- sis, strep throat, diphtheria, pertussis, legionellosis, influenza, and chicken pox, and a wide range of mycotic diseases such as aspergillosis, zygomycosis, cryptococcosis, histoplasmosis, and coccidioidomycosis.

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MAJOR CATEGORIES OF PATHOGENIC MICROORGANISMS

Viruses

Believed to be a bridge between the living and the nonliving, viruses have either DNA or RNA, seldom both. Their genome is surrounded by a protein coat, called capsid. Certain viruses have an envelope, often derived from the host cell membrane during lysis and release. Multiple characteristics, including type of nucleic acid, single or double strands, and presence or absence of envelope, are taken into account in the classification of viruses.

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