Merck Manual

Please confirm that you are a health care professional

Loading

Introduction to the Biology of Infectious Diseases

By

Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University

Last full review/revision Jul 2020| Content last modified Jul 2020
Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version

A healthy person lives in harmony with the microbial flora that helps protect its host from invasion by pathogens, usually defined as microorganisms that have the capacity to cause disease. The microbial flora is mostly bacteria and fungi and includes normal resident flora, which is present consistently and which promptly reestablishes itself if disturbed, and transient flora, which may colonize the host for hours to weeks but does not permanently establish itself. Organisms that are normal flora can occasionally cause disease, especially when defenses are disrupted.

Tropisms (attractions to certain tissues) determine which body sites microorganisms colonize. Normal flora is influenced by tropisms and many other factors (eg, diet, hygiene, sanitary conditions, air pollution). For example, lactobacilli are common in the intestines of people with a high intake of dairy products; Haemophilus influenzae colonizes the tracheobronchial tree in patients with COPD (chronic obstructive pulmonary disease). As a result, different body habitats contain microbial communities, forming microbiomes that differ by microbial composition and function.

Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
Professionals also read

Also of Interest

Videos

View All
How To Wash Your Hands
Video
How To Wash Your Hands
3D Models
View All
SARS-CoV-2
3D Model
SARS-CoV-2

SOCIAL MEDIA

TOP