Bacterium by Cause & Disease

Bacteria play a huge role in our day-to-day life, living on and in us, carrying out a number of functions in symbiosis with our bodies. Called "normal flora," there are actually many types of harmless bacteria, fungi, and archaea that are always present in humans. However, there are a number of bacteria that may attack our bodies and cause disease. These disease-causing bacteria use a handful of different transmission methods and vary widely in severity.

Airborne and Droplet Contact

• Some disease-causing bacteria are transmitted through tiny droplets of saliva, expelled via sneeze or cough. A person may become infected if these droplets come in contact with her eyes, nose, or mouth. This is called droplet contact transmission. Many disease-causing bacteria that spread this way may also be spread via airborne transmission (and vice versa). In airborne transmission the droplets evaporate and remain suspended in the air. However, some airborne diseases reside on dust particles. Some disease-causing bacteria spread through airborne and droplet transmission are Streptococcus pyogenes (strep throat), Streptococcus pneumonia (pneumococcal pneumonia), Mycoplasma pneumonia (primary atypical pneumonia), Mycobacterium tuberculosis (tuberculosis), Bordetella pertussis (whooping cough), and Neisseria meningitides (meningococcal meningitis).

Direct Contact

• Certain bacteria require skin-to-skin contact or contact with biological material in order to transmit. These bacteria usually cannot survive very long outside of a host. Common disease-causing bacteria transmitted via direct contact include Staphylococcus aureus (staph infection), Chlamydia trachomatis (trachoma), Haemophilus influenzae type III (bacterial conjunctivitis), and Mycobacterium leprae (leprosy).

  Sexual transmission (transmission via sexual contact) is a specific form of direct contact transmission. Bacterial sexually transmitted diseases (STDs) include chlamydial urethritis (Chlamydia trachomatis), gonorrhea (Neisseria gonorrhoeae), and syphilis (Treponema pallidum).

Indirect Contact

• Indirect contact transmission occurs when a bacterium able to survive for long periods of time outside of a host uses some nonbiological agent, like a doorknob, medical instrument, or dirt, as a medium for transmission. Some disease-causing bacteria that can transmit through indirect contact are Clostridium tetani (tetanus), Bacillus anthracis (anthrax), and Clostridium perfringens (gas gangrene). Some bacteria that normally transmit via other means may also transmit by means of indirect contact in optimal conditions.

Fecal-oral

• Fecal-oral transmission occurs when someone swallows contaminated food or water. Bacteria that use this method of transmission primarily infect the digestive system. Some of these include Clostridium botulinum (botulism), Salmonella typhi (typhoid fever), Salmonella serotypes (salmonellosis), and Vibrio cholera (cholera).

Vector-borne

• Vector-borne bacteria are those transmitted through the bite, sting, or fecal droppings of an animal or insect. Mosquitoes, dogs, ticks, rats, and mites are some of the creatures that may act as disease-spreading vectors. Rickettsia prowazekii (typhus fever), Yersinia pestis (bubonic plague), and Rickettsia rickettsii (Rocky Mountain spotted fever) are examples of vector-borne disease-causing bacteria.