Bacteria are single-celled microorganisms found in several different habitats on earth. While many bacteria play a vital role in processes; such as nitrogen fixation and maintaining soil fertility, some of these organisms cause diseases in humans and animals. Such organisms are called pathogenic bacteria. They have the capacity to spread from an infected individual to another through diverse modes such as air, water, insects, animals and an exchange of body fluids.
Transmission of bacteria can occur through physical contact with an infected individual. Contact with lesions on the person's body, hugging, kissing and sexual contact are examples of actions that pose a risk of transmitting bacteria. Besides family members, this type of transmission is possible from a patient to hospital staff involved in bathing or caring for patients. Diseases such as syphilis, gonorrhoea and tetanus spread through direct contact.
Transmission by indirect contact refers to situations when bacteria move from an inanimate object to a susceptible individual. For example, doorknobs, tables, chairs, beds, dishes, trays, electronic device buttons, computer keyboards, telephones and toys are capable of retaining bacteria on their surface. These bacteria then transfer to the body of the person who comes into contact with these surfaces. In hospital settings, contaminated objects such as unwashed hands, used gloves and unsterilised medical instruments may transmit bacteria.
When an infected person sneezes or coughs, there is a generation of droplets that carry bacteria. These droplets do not remain hanging in the air; they tend to settle on available surfaces. When the droplets come into contact with the tissues of an individual's eyes, mouth and nose, he picks up those bacteria. To avoid such transmission, it is important to use protective measures such as masks and goggles. SARS and measles are two diseases that spread through droplet contact.
When bacteria-containing droplets evaporate, they leave behind a residue that remains hanging in the air. These enter an individual's respiratory system when he breathes in the air. Similarly, dust particles in the air in a contaminated area may also transmit bacteria. Tuberculosis, diphtheria and pertussis are infections that spread through airborne transmission.
Vector Borne Transmission
Certain bacteria spread through animals and insect carriers such as dogs, rats, flies, ticks, fleas and mites. When an individual is bitten by one of these vectors, she picks up the bacterial infection. Bacteria that spread through such means cause infections to spread further than by the other methods. These vectors may also transmit bacteria through their faeces that come in contact with solid surfaces or water. Vector borne transmission can be prevented by taking measures to keep these insects and animals away. Leptospirosis and bubonic plague are examples of bacterial infections transmitted through vectors.
In case of poor hygiene, minute quantities of an infected person's faeces may be passed on to a surface or to food and water the person handles. This leads to a transmission of the bacteria from him to the object and subsequently to others who come in contact with it. Salmonella and shigella infections spread through this mode of transmission.