1. Microbiology Basics

• Pages: 1-19
• Author: Marc W. Mittelman, PhD

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Microbiology Basics

Marc W. Mittelman, PhD1

In the invisible world of microorganisms, pathogens (also called

germs) are the ones that typically cause disease. This chapter

describes our evolving understanding of the microbial world,

along with the types of tests and methodologies used to explore

causative links between microorganisms and disease. Along the

way, it introduces lawyers and other nonscientist readers to a large

number of specialized terms that they may encounter in expert

reports and other writings in the microbiology eld.

Microorganisms are life forms that cannot be seen with the

unaided eye; therefore, you must use a microscope to see them.

The microbial world may be broadly divided into groups that include

viruses, archaea, bacteria, fungi, microalgae, and protozoa. Micro-

biology involves the study of these taxonomic groups in the context

of both their benecial and their harmful effect on our health and

wellbeing. Various subdisciplines include infectious disease detection,

treatment, and control (clinical microbiology, infectious disease micro-

biology, and public health microbiology); environmental applications

and impacts (environmental microbiology); industrial applications

1. Marc Mittelman is a Senior Managing Scientist in Health Sciences at Exponent Inc.

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and impacts, including pharmaceutical and biotechnology applications

(industrial microbiology); and food, dairy, and beverage manufactur-

ing (food microbiology). As professionals, microbiologists tend to

focus their work on one group of microorganisms, and they are often

specialists in a specic discipline, such as clinical microbiology.

Although most of the public associates microorganisms only with

diseases such as inuenza and strep throat, microorganisms are ubiq-

uitous throughout virtually every environment on earth. Microor-

ganisms are essential for life in aquatic and terrestrial environments.

Humans and other animals depend on the activities of a diverse array

of microorganisms for digestion, essential vitamin production, and

other functions that are essential for a healthy life. There are also

numerous commercial products and processes that require microor-

ganisms to function as chemical factories.

Despite their ubiquitous nature, only a minority of microorganisms

are typically associated with disease processes in humans. Pathogens

are microorganisms that overcome the host’s immune system and cause

disease. Many textbooks describe frank or opportunistic pathogens as

microorganisms that will cause disease in virtually any host or only in

a susceptible host, respectively. However, it is known that virtually any

microorganism can cause an infection in humans if an individual is com-

promised by preexisting conditions (e.g., diabetes, heart disease, can-

cer), by advanced age, or through intrinsic immune system deciencies.

An outbreak is dened as an abnormal increase in the number of

cases for a specic disease in a dened time, geographical area, or

distribution system, which affects a denable group of individuals.

When the increase in cases extends more broadly, the event is charac-

terized as an epidemic. For an outbreak to occur, one or more of the

following conditions typically exist:2

• The microbial agent has recently increased in number (some-

times referred to as titer) or virulence (dened as the degree of

pathogenicity).

• The agent has recently been introduced into a setting where it

has not been before.

2. Kelsey JL, Thompson WD, Evans AS. Methods in Observational Epidemiology.

Oxford University Press; 1986.

2 Infectious Disease Litigation

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