Microbes That Cause Disease

Since the development of the germ theory, many scientists, working with plant and animal infecting microbes, have focused their research efforts on the microbes that cause disease (Ainsworth, 1981). Endophytes (fungi and/or bacteria that live within the tissues of plants) largely appear to be the inverse of plant pathogens since generally they represent cryptic benign infections of healthy plants. The term endophyte (Gr. endon, within; phyton, plant) was first coined by De Bary (De Bary, 1866) and an endophyte is a bacterial or fungal microorganism, which spends the whole or part of its life cycle colonizing inter- and/or intra-cellularly inside the healthy tissues of the host plant, typically causing no apparent symptoms of disease (Wilson,

Microorganisms are considered as miniatures of chemical factories. Until Pasteur showed that fermentation is initiated by living organisms and showed that lactic acid fermentation is caused by living organisms that people seriously began to investigate microbes as a source for bioactive natural products. Then, scientific serendipity and the power of observation provided the impetus to Fleming to usher in the antibiotic era via the discovery of penicillin from the fungus Penicillium notatum. After which, array of bioactive metabolites was isolated from microorganisms including fungi, bacteria and actinomycetes. Fleming in 1929 discovered the serendipitous penicillin from the filamentous fungus, Penicillium notatum, and he discovered the broad therapeutic use of this agent in the 1940s (Demain and Fang, 2000). This ushered a new era in medicine, the so-called Golden Age of Antibiotics (Mann, 1994). In spite of this until 1970 only two classes of naturally occurring β-lactam antibiotics, penicillins and cephalosporins, were known. With the advent of new screening and isolation techniques, a variety of β-lactam-containing molecules (Wells et al., 1992) and other types of antibiotics have been identified. This discovery promoted the intensive investigation of nature as a source of novel bioactive agents, and microorganisms