The discovery of many disease-causing organisms dates back to the 1800s. You may have heard of many infectious diseases from this era but have not experienced them first-hand. This is especially true if you were born within the last 30 to 50 years. Today, the frequency and incidence of many diseases have markedly decreased because of improvements in standard of living, sanitation and access to health care.
Groups of bacteria (Genus) can be made up of thousands of different strains (species). Some of the most common disease-causing organisms are:
Streptococcus - responsible for a wide variety of conditions with very different symptoms
Escherichia - found naturally in the gastrointestinal tract where it suppresses the growth of harmful bacteria and synthesizes vitamins. Only some of these can cause disease.
Clostridium - the toxins produced by this strain make it one of the most dangerous disease-causing organisms
Salmonella - there are over 2,000 different species of Salmonella responsible for a variety of ailments
Staphylococcus - found naturally on the skin. It may also cause infections in patients whose immune system has been compromised.
Mycobacterium - responsible for many debilitating diseases
Bacillus - harmless species inhabit the mucus lining of our stomachs and intestines. However, some Bacillus may cause infectious diseases.
Shigella - a family of bacteria that cause diarrhea in humans ("shigellosis")