**2.1. Pre-antibiotic era**

Before the early 20th century, treatments for infections were based primarily on medicinal folklore. Mixtures with antimicrobial properties that were used in treatments of infections were described over 2000 years ago [1]. Even the prehistoric peoples used a number of plants in wound treatment and it seems possible that many plants have the properties of an‐ timicrobial effects [2; 3]. Tetracyclines can be incorporated into the hydroxyapatite mineral portion of bones as well as tooth enamel; once people take it, permanent markers of meta‐ bolically active areas will be left. Thus it is much conveniently to trace the exposure of these

© 2013 Yanling et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

antibacterials in ancient populations. It was found than the bone sample from Sudanese Nu‐ bian (A.D. 350 to 550) was labeled by the antibiotic tetracycline and their dietary regime con‐ tained tetracycline-containing materials by X-group cemetery and other advanced technologies [4; 5]. Moreover, another study showed that, bones from the Dakhleh Oasis, Egypt, in a late Roman period, exhibit discrete fluorochromelabelling, exactly like the teeth from patients treated with tetracycline [6]. A large number of customs and anecdotes can al‐ so reveal the occurrences of other antibacterials. One popular anecdote is about the antibiot‐ ic-like properties of red soil from the Hashemite Kingdom of Jordan. Interestingly, red soil was used for treating skin infections and diaper rash in the past and is still used in some communities today as an inexpensive alternative to antibiotics [7]. In fact, recently, many pharmaceutical antibiotics, such as streptomycin, actinomycin, erythromycin, vancomycin, nystatin and amphotericin, were produced from the soil actinomycetes [8].

The effect of mould on bacterial colonies hadn't been investigated until 19th century, al‐ though the antibacterial properties of mold had been known since ancient times. In 1921, Alexander Fleming observed some substances called lyzosomes which could dissolve bacte‐ ria. In 1928, he discovered that a specific mould species inhibited the development of Staph‐ ylococcus bacteria. The species was known as Pencilliumnotatum and the filtrate was called penicillin [15]. In 1940, Howard Florey and Ernst Chain worked out how to purify penicillin for clinical testing [16]. All the three researchers were awarded the Nobel Prize in 1945, and since then the era of antibiotics had been initiated. Penicillin became the top therapeutic molecule because of its widespread use and the magnitude of the therapeutic outcomes, and also because of the technologies developed for production of penicillin which became the basis for production of all subsequent antibiotics and other bioproducts in use today [17].

The Antibacterial Drug Discovery http://dx.doi.org/10.5772/52510 291

Antibacterials are commonly classified based on their mechanism of action or spectrum of activity. The main classes of antibacterial drugs target only four classical bacterial functions: bacterial-cell-wall biosynthesis (e.g., penicillin and vancomycin); bacterial protein biosynthe‐ sis (e.g., aminoglycoside and macrolide); DNA and RNA replication (e.g., ciprofloxacin and rifampin); and folate coenzyme biosynthesis (e.g., sulfamethoxazole) [18]. Antibacterials that target the cell wall or cell membrane or essential bacterial enzymes are more likely to be bac‐ tericidal; but generally the bacteriostatic is the antibacterial drugs that inhibits protein syn‐ thesis [19]. Another way to distinguish the antibiotics is based on their target specificity. The broad-spectrum antibiotic affects a wide range of disease-causing bacteria, including both Gram-positive and Gram-negative bacteria, in contrast to a narrow-spectrum antibiotic, which acts against specific families of bacteria. For example, ampicillin is a widely used

Bacterial resistance to antibacterial drugs increasingly becomes a major health and economic problem, eroding the discovery of antibiotics and their application to clinical medicine. As early as 1946, Alexander Fleming predicted that "There is probably no chemotherapeutic drug to which in suitable circumstances the bacteria cannot react by in some way acquiring 'fastness' (resistance)." Today it is really the truth. Resistance to the antibiotics will emerge only a few years after it is introduced to clinic use [20]. Bacterial resistance is positively cor‐ related with the use of antibacterial agents in clinical practice [21; 22]. Because any use of antibiotics can increase selective pressure in a population of bacteria, allowing survival of the resistant bacteria and death of the susceptible ones. We can find that pathogenic bacteria are resistant to practically all available antibacterial drugs. And many strains, which are in‐ formally called superbugs, are even resistant to several different antibiotics. Multidrug re‐ sistance has been found in Pseudomonas aeruginosa (P. aeruginosa),

**3. Classification**

broad-spectrum antibiotic.

**4. Antibacterial resistance and its mechanisms**

The traditional Chinese medicine is the summary of experience about Chinese medical treat‐ ment over millennia and may contain a lot of unknown antibiotics [9]. Many traditional Chi‐ nese medicines were tested and found effective against four common oral bacteria [10]. Discovery of active components in the ancient herbs could enrich the arsenal of antimicrobi‐ als used by the mainstream medicine.
