Chapter 14: Microbe-Human Interactions

We Are Not Alone

• Human body exists in a state of dynamic equilibrium

• Many interactions between human body and microorganisms involve the development of biofilms

• Colonization of the body involves a constant “give and take”

Contact, Colonization, Infection, Disease

• Normal (resident) Flora, Indigenous Flora, Microbiota: Microbes that engage in mutual or commensal associates

• Infection: Condition in which pathogenic microbes penetrate host defenses, enter tissues, and multiply

• Pathogen: Infectious agent

• Infectious Disease: Infection that causes damage or disruption to tissues and organs

Pathology, Infection, and Disease

• Pathology: Study of disease

• Etiology: Cause of a disease

• Pathogenesis: Abnormal state in which the body is not performing normal functions

Resident Flora

• Most areas of the body in contact with the outside environment harbor resident microbes

• Internal organs, tissues, and fluids are microbe-free

• Transients: Microbes that occupy the body for only short periods

• Residents: Microbes that become established

Resident Flora (continued)

• Microbial Antagonism: Bacterial flora benefit host by preventing overgrowth of harmful microbes

  • Normal Microbiota:

  • Competing for nutrients

  • Producing substances harmful to invading microbes

  • Affecting pH and available oxygen

  • Endogenous Infections: Occur when normal flora is introduced to a site that was previously sterile

Initial Colonization of the Newborn

• Uterus and contents are normally sterile and remain so until just before birth

• Breaking of fetal membrane exposes the infant; all subsequent handling and feeling continue to introduce what will be normal flora