Key Notes

Microbiology is the ‘biology of microscopic organisms’.

Medical microbiology is the study of microbes that cause disease in humans.

Microbes are everywhere, both within and outside our body. Most are harmless.

Microbes vary in shape, size and structure and are categorized into eukaryotic (fungi, worms and protozoa), prokaryotic (bacteria, rickettsia and chlamydia) or noncellular (viruses and prions). Eukaryotic organisms are uni- or multicellular; prokaryotes are unicellular. Viruses and prions are incapable of independent life.

Epidemiology is the study of spread of infection, including the source, transmission, distribution and prevalence of infection in the community.

Sources of infection are either endogenous or exogenous. Acquisition of pathogens may occur via many routes, including direct contact, inhalation, ingestion, injection or vertical transmission.

Epidemiologists assess infection in a community by using various measurements, including incubation period of disease, incidence, prevalence, attack rate and mortality rate.

Infection is a generic term used to indicate invasion of the host by a microorganism.

Infection may be subclinical or asymptomatic when the patient is unaware of the infection. Clinical infection is associated with the presence of overt signs and symptoms of disease.

The term ‘colonization’ should be restricted to the presence of a microbe at an expected site.

A pathogen is a microbe that potentially can cause harm, i.e. tissue damage. An opportunistic pathogen is a microbe that causes infection in patients with impaired immunity, e.g. fungal infections in cancer patients.