Chapter 4 – The Human Microbiome (OpenStax Microbiology)

Vocabulary flashcards summarizing key terms and concepts about the human microbiome, its establishment, influencing factors, and impact on health.

Microbiome

The collective community of all microbes (bacteria, archaea, fungi, viruses, etc.) that live in or on a host organism.

Microbe

A microscopic organism, such as a bacterium, fungus, protozoan, or virus, that can inhabit the human body.

Normal microbiota

Microbial species that colonize a host long-term without causing disease under normal conditions; also called resident microbes, normal flora, or commensals.

Resident microbes

Synonym for normal microbiota—microbes that are permanently established on or within the body.

Normal flora

Older term for the normal microbiota that inhabit the human body.

Commensals

Microbes that derive benefit from the host without harming it; a major component of the normal microbiota.

Human Microbiome Project (HMP)

A research initiative that studies relationships between human-associated microbial communities and health or disease.

Transient microbiota

Microbes that colonize the host for days, weeks, or months but do not establish permanent residence.

Opportunistic infection

Disease caused when a normally harmless microbe takes advantage of a disrupted microbiome or weakened host defenses.

In utero colonization

Initial establishment of a few microbes in a fetus before birth.

Vaginal birth microbiome

Newborns delivered vaginally acquire microbiota rich in Lactobacillus and Bacteroides from the mother’s birth canal.

Cesarean birth microbiome

Infants born by C-section have a microbiome resembling human skin, dominated by Staphylococcus species.

Lactobacillus

Genus of lactic-acid–producing bacteria commonly found in the vaginal canal and acquired by babies during vaginal delivery.

Bacteroides

Genus of obligate anaerobic bacteria that can make up ~30 % of the normal human gut microbiota.

Staphylococcus epidermidis

Common skin bacterium often dominant in the microbiome of infants delivered by Cesarean section.

Antagonism (microbial)

Protective effect in which resident microbes compete for space and nutrients, alter pH, or produce compounds that inhibit pathogens.

Immune system training

Process by which exposure to the microbiome helps the host immune system learn to distinguish pathogens from non-pathogens.

Disruption of the microbiome

Disturbance (e.g., antibiotics) that reduces normal microbes and increases risk of infection by pathogens.

Antibiotic-associated yeast infection

Overgrowth of Candida species (vaginitis or thrush) after antibiotics diminish normal bacterial flora.

Clostridioides difficile colitis

Severe intestinal infection that can occur when antibiotics disrupt normal gut microbiota, allowing C. difficile to proliferate.

Factors influencing the microbiome

Age, hormones, immunity, diet, stress, lifestyle, nutrient availability, pH, moisture, oxygen, and mechanical forces affect microbial composition.

Mechanical factors

Physical processes such as skin shedding or intestinal peristalsis that influence where microbes can reside.