Antimicrobial agents Introduction • antibiotics- are natural substances produced by certain groups of microorganisms • chemotherapeutic agents - are chemically synthesized. • A hybrid substance is a semisynthetic antibiotic, wherein a molecular ver

Antimicrobial agents Introduction • antibiotics- are natural substances produced by certain groups of microorganisms • chemotherapeutic agents - are chemically synthesized. • A hybrid substance is a semisynthetic antibiotic, wherein a molecular version produced by the microbe is subsequently modified by the chemist to achieve desired properties • The modern era of antimicrobial chemotherapy began in 1929, with Fleming's discovery of the powerful bactericidal substance, penicillin, and Domagk's discovery in 1935 of synthetic chemicals (sulfonamides) with broad antimicrobial activity. Microorganisms that produce antibiotics 1. Penicillium and Cephalosporium molds produce beta-lactam antibiotics such as penicillin and cephalosporin and their relatives. They also produce the base molecule for development of semisynthetic beta-lactam antibiotics, such as amoxacillin and ampicillin. Beta-lactams are used to treat about one-third of outpatients with bacterial infections. The natural habitat of molds is soil. And although sex is sometimes involved, they reproduce by spore formation. They are foremost in their abilities to degrade organic matter, and they play their most important role in natures in biodegradation and the carbon cycle. Most of us know that molds will grow on nearly anything that is organic and moist, so they are also responsible for a lot food spoilage as well as decomposition of our structural materials and textiles. "Nothing is forever", with molds around Cont,.. 2. Actinomycetes, mainly Streptomyces species, produce tetracyclines, aminoglycosides (streptomycin and its relatives), macrolides (erythromycin and its relatives), chloramphenicol, ivermectin, rifamycins, and most other clinically-useful antibiotics that are not beta-lactams. Actinomycetes are the mainstay of the antibiotics industry. Actinomycetes are a group of branched bacteria that reproduce by spore formation. They come from a phylum of Bacteria, Actinobacteria, and they are landed in Order Actinomycetales. Some of the representative family include such diverse bacteria as Actinomyces, Cory`nebacterium, Nocardia, Propionibacter, Streptomyces, Micromonospora and Frankia. Most actinomycetes are inhabitants of the soil. The characteristic odor of damp soil is due to the production of substances, called geosmins, by these bacteria 3. Bacillusspecies, such as B. polymyxa and B. subtilis, produce polypeptide antibiotics (e.g. polymyxin and bacitracin), and B. cereus produces zwittermicin. Bacillus species have the relatively rare ability to form a type of resting cell called an endospore. Bacilli are Gram-positive, rod-shaped, aerobic bacteria that live in the soil. They play an important ecological role in aerobic decomposition, biodegradation and mineral recycling.