Toilets house a large amount of germs, particularly toilets in public establishments. Interestingly, however, the floor of the bathroom actually contains more germs than the toilet bowl, as explained in a 2005 report by ABC News. Tests at the University of Arizona revealed that 62 percent of bathroom floors were contaminated with potentially dangerous bacteria, as compared to 19 percent of toilet bowls. Nonetheless, toilet bowls can contain some nasty bacteria, and proper hand washing is the best way to prevent infection.
Shigellosis is a gram-negative bacteria that is found in toilet bowls. The bacteria can cause a wide range of symptoms, including severe diarrhea and dysentery. The bacteria cause inflammation of the intestines and are usually passed in fecal matter. According to Merck online, one of the common ways that shigellosis bacteria are spread is when food workers fail to wash their hands after using the toilet.
Staphylococcus bacteria can be hard to kill, particularly the methicillin-resistant strain known as MRSA. According to the San Diego County Health and Human Services Agency, MRSA is spread by person-to-person contact and is often harbored in toilet bowls. If MRSA is suspected in a home or community, the toilet bowl and seat should be disinfected once daily with a strong cleaning solution.
Salmonella are often found in toilet bowls. These harmful bacteria can cause severe vomiting and diarrhea in affected persons. A 2000 study by scientists at the UK's Aston University School of Health and Life Sciences examined the household conditions of six families who had recently suffered from a salmonella outbreak. In four out of six homes, salmonella bacteria were found in the toilet bowl, specifically under the water line.
Fortunately, not all bacteria in the toilet bowl cause illness. Serratia marcescens, a very common bacteria in toilet bowls and the environment in general, can cause a pink or gray lining inside the toilet bowl that may cause alarm. Although the bacteria can be harmful to a small ratio of people and cause illness such as urinary tract infections and pneumonia, they are generally harmless and removable with the aid of chlorine bleach.