Antibiotics also called antibacterials, are a type of antimicrobial drug used in the treatment and prevention of bacterial infections.They 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 influenza; drugs which inhibit viruses are termed antiviral drugs or antivirals rather than antibiotics. In 1926, Alexander Fleming discovered penicillin, a substance produced by fungi that appeared able to inhibit bacterial growth. Another antibiotic, for example, is tetracycline, a broad-spectrum agent effective against a wide variety of bacteria including Hemophilus influenzae, Streptococcus pneumoniae, Mycoplasma pneumoniae, Chlamydia psittaci, Chlamydia trachomatis, Neisseria gonorrhoea, and many others.