Shape, Arrangement, and Size
It might be expected that bacterial cells, being small and relatively simple, would be uniform in shape and size. This is not the case, as the microbial world offers considerable variety in terms of morphology. However, the two most common shapes are cocci and rods. Cocci Cocci (s., coccus) are roughly spherical cells. They can […]
Major Fields in Microbiology
Pathogenic microbes, though relatively few in number, have had and continue to have considerable impact on humans. Thus one of the most active and important fields in microbiology is medical microbiology, which deals with diseases of humans and animals. Medical microbiologists identify the agents causing infectious diseases and help plan measures for their control and […]
Microorganisms and Disease
Although Fracastoro and a few others had suggested that invisible organisms produced disease, most people believed that disease was caused by supernatural forces, poisonous vapors called miasmas, and imbalances among the four humors thought to be present in the body. The role of the four humors (blood, phlegm, yellow bile [choler], and black bile [melancholy]) […]
Microscopy and the Discovery of Microorganisms
The earliest microscopic observations of organisms appear to have been made between 1625 and 1630 on bees and weevils by the Italian Francesco Stelluti (1577-1652), using a microscope probably supplied by Galileo (1564-1642). Robert Hooke (1635-1703) is credited with publishing the first drawings of microorganisms in the scientific literature. In 1665 he published a highly […]
Introduction to Microbiology
Microorganisms are defined as those organisms and acellular biological entities too small to be seen clearly by the naked eye They are generally 1 millimeter or less in diameter. Although small size is an important characteristic of microbes, it alone is not sufficient to define them. Some cellular microbes, such as bread molds and filamentous […]
Carbon Cycle
Carbon is the element that defines life, and as such it is everywhere. The exchange of elements between sources and sinks is referred to as flux. Carbon is present in reduced forms, such as methane (CH4) and organic matter, and in more oxidized forms, such as carbon monoxide (CO) and carbon dioxide (C02). Carbon fixation Although […]
Protein Synthesis Inhibitors
Many antibiotics inhibit protein synthesis by binding with the bacterial ribosome and other components of protein synthesis. Because these drugs discriminate between bacterial and eukaryotic ribosomes, their therapeutic index is fairly high but not as high as that of cell wall synthesis inhibitors. Several different steps in protein synthesis can be affected by drugs in […]
Cell wall Inhibitor
Penicillins Most penicillins (e.g., penicillin G or benzylpenicillin) are derivatives of 6-aminopenicillanic acid and differ from one another with respect to the side chain attached to the amino group. The most crucial feature of the molecule is the B-lactam ring, which is essential for bioactivity. Many penicillin resistant bacteria produce penicillinases (also called beta-lactamases), enzymes […]
Characteristics of Antimicrobial Drugs
As Ehrlich so clearly saw, a successful chemotherapeutic agent has selective toxicity: it kills or inhibits the microbial pathogen while damaging the host as little as possible. The degree of selective toxicity may be expressed in terms of (1) the therapeutic dose-the drug level required for clinical treatment of a particular infection, and (2) the […]
Penicillin
Penicillin, the first true antibiotic because it is a natural microbial product, was first discovered in 1896 by a twenty-one-yearold French medical student named Ernest Duchesne. His work was forgotten until Alexander Fleming accidentally rediscovered penicillin in 1928. After returning from a weekend vacation, Fleming noticed that a Petri plate of Staphylococci also had mold […]