Bacterial Disease

Most bacteria are either beneficial or harmless to humans – those that cause disease are pathogens:

- The symptoms of the disease are usually caused by waste products of the pathogens

- An infection is when the effects are noticeable on the body

- Transmission is when an infection is passed on to somebody else


Diseases such as typhoid and cholera are transmitted through water, and can cause diarrhoea

To avoid water contamination, water-treatment processes take place


Food-borne infections including Salmonella are spread in two ways:

- By not cooking food thoroughly (e.g. raw eggs: newly laid eggs may be contaminated with poultry faeces)

- By contaminating cooked meat from handling raw meat first e.g. chicken


Air-borne infections are spread when an infected person coughs, sneezes, talks or breathes, as the pathogens are passed into the air in small droplets saliva, mucus and water

Infections that can be transmitted by direct contact are said to be contagious

Insect bites can transmit pathogens through the saliva of the insect


Pathogenicity is the ability of a bacterium to cause disease.

The main factors are:

- The way in which the bacterium attaches and gains entry to host cells

- The types of toxin produced by the bacterium

- The infectivity of the bacterium (the number needed to cause an infection)

- The invasiveness of the bacterium (its ability to spread within the host)


After infection, a pathogen must do three things in order to produce a disease:

- Attachment

- Entry (penetration)

- Colonisation