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Antibiotics are the chemical substances produced by microorganisms such as bacteria and fungi that are capable of destroying or inhibiting the growth of microorganismsThey may either kill or inhibit the growth of bacteria. A limited number of antibiotics also possess antiprotozoal activity. Antibiotics are not effective against viruses such as the common cold or influenzadrugs that inhibit viruses are termed antiviral drugs or antivirals rather than antibiotics.


In 1928, Sir Alexander Fleming postulated the existence of penicillin, a molecule produced by certain molds that kill or stop the growth of certain kinds of bacteria. Fleming was working on a culture of disease-causing bacteria when he noticed the spores of a green mold, Penicillium chrysogenum, in one of his culture plates. He observed that the presence of the mold killed or prevented the growth of the bacteria. Fleming postulated that the mold must secrete an antibacterial substance, which he named penicillin in 1928.

Most Commonly used antibiotics

1. Penicillins

Another name for this class is the beta-lactam antibiotics, referring to their structural formula. The penicillin class contains five groups of antibiotics: aminopenicillinsantipseudomonal penicillinsbeta-lactamase inhibitorsnatural penicillins, and penicillinase resistant penicillins.

2. Tetracyclines

Tetracyclines are broad-spectrum against many bacteria and treat conditions such as acne, urinary tract infections (UTIs), intestinal tract infections, eye infections, sexually transmitted diseases, periodontitis (gum disease), and other bacterial infections. 

3. Cephalosporins

There are five generations of cephalosporins, with increasing expanded coverage across the class to include gram-negative infections. Newer generations with updated structures are developed to allow wider coverage of certain bacteria. Cephalosporins are bactericidal (kill bacteria) and work in a similar way as penicillins. Cephalosporins treat many types of infections, including strep throat, ear infections, urinary tract infections, skin infections, lung infections, and meningitis.

Types of Antibiotics

There are various antibiotics available and they come in various different brand names. Antibiotics are usually grouped together based on how they work. Each type of antibiotic only works against certain types of bacteria or parasites. This is why different antibiotics are used to treat different types of infection. The main types of antibiotics include:

·         Penicillins – for example, phenoxymethylpenicillinflucloxacillinamoxicillin.

Cephalosporins- for example, cefaclorcefadroxil and cefalexin.

·         Tetracyclines - for example, tetracyclinedoxycycline, and lymecycline.

·         Aminoglycosides - for example, gentamicin and tobramycin.

·         Macrolides-for example, erythromycinazithromycin, and clarithromycin.

·         Clindamycin.

·         Sulfonamides and trimethoprim - for example, co-trimoxazole.

·         Metronidazole and tinidazole.

·         Quinolones - for example, ciprofloxacinlevofloxacin, and norfloxacin.

·         Nitrofurantoin - used for urinary infections.


Applications of antibiotics

1. Antitumor antibiotics::

There are a selected few antibiotics that are in use for control of cancer growth, although with limited success e.g. actinomycin D, mitomycin C.

2. Food preservative antibiotics:

Certain antibiotics are used in the canning industry (e.g. chlortetracycline), and for the preservation of fish, meat, and Poultry (e.g. Pimancin nisin). The use of antibiotics in food Preservation is usually under the control of the Governments.

3. Antibiotics used in animal feed and veterinary medicine:

Till some time ago, antibiotics (penicillins, tetracyclines, erythromycins) were very widely used in the processing of animal feeds. Such an indiscriminate use resulted in the development of antibiotic resistance in animals and humans. A new class of antibiotics has been developed for specific use in animal feed e.g. enduracidin, tylosin. Likewise, specific antibiotics have been developed for exclusive use in veterinary medicine e.g. hygromycin B, thiostrepton, salinomycin.

4. Antibiotics for control of plant diseases:

In recent years, several antibiotics have been developed for exclusive use to control plant diseases e.g. blasticidin, tetranactin, polyoxin.

5. Antibiotics as tools in molecular biology:

Some of the antibiotics can selectively inhibit certain biological reactions at the molecular level. These antibiotics do in fact serve as tools for exploring the knowledge of life sciences. Thus, certain antibiotics have been used to obtain some important information on DNA replication, transcription, and translation.