The development of resistant strains of disease-causing microorganisms is an important health issue of global concern. When microbes such as bacteria, fungi, parasites, and viruses become resistant to antimicrobial substances, the diseases they may cause become more difficult or impossible to treat. Resistance is developed by the indiscriminate use of antimicrobials and places human health at risk. The discovery of antibiotics revolutionised medicine, creating a belief that a 'magic bullet' had finally been found to control bacterial diseases. Antibiotics, a class of antimicrobial agents, kill or inhibit the growth of bacteria, but they have no significant effect on other types of microorganisms such as viruses.