The community of microorganisms that naturally inhabit a specific environment or host, often referred to as normal flora or microbiota.
Explanation
Microbial flora describes the assemblage of bacteria, archaea, fungi and other microorganisms that colonize a particular niche, whether it is the human gut, skin, oral cavity, vagina or a natural habitat like soil or water. These communities are often stable and coevolved with their host or environment, providing essential functions such as nutrient metabolism, vitamin synthesis and protection against pathogenic invaders. In humans, microbial flora is established shortly after birth and influenced by factors such as mode of delivery, diet, antibiotic exposure and genetics. The term “flora” originates from a time when microbes were likened to plants; modern usage often prefers “microbiota”, but the concept remains the same.
Resident flora consists of long-term inhabitants adapted to their niche, while transient flora includes microbes that temporarily colonize surfaces and are often removed by host defenses or environmental conditions. Maintaining a balanced microbial flora is important for health; disruptions can lead to dysbiosis, allowing opportunistic pathogens to proliferate or altering metabolic processes. For example, broad-spectrum antibiotic use can diminish gut flora, leading to overgrowth of Clostridioides difficile and diarrhoea. Beyond human hosts, microbial flora of soils, oceans and other ecosystems drive biogeochemical cycles and support plant growth.
Sites and Functions
The gastrointestinal tract harbours one of the densest microbial communities, dominated by anaerobic bacteria such as Bacteroides, Firmicutes and methanogenic archaea. These microbes ferment complex carbohydrates, produce short‑chain fatty acids and synthesize vitamins like K and B12. Skin flora includes Staphylococcus epidermidis, Propionibacterium acnes and yeasts that contribute to skin barrier function and inhibit pathogenic colonization. The female genital tract is typically dominated by Lactobacillus species that produce lactic acid to maintain a low pH. In soil, microbial flora includes nitrifying bacteria, actinomycetes and mycorrhizal fungi that decompose organic matter and assist plants in nutrient uptake.
Recognizing the roles of microbial flora highlights the symbiotic relationships between hosts and their microbial inhabitants. Understanding these communities informs approaches to maintain health, manage infections and harness beneficial microbes in agriculture and environmental management.
Related Terms: Commensal, Microbiota, Normal flora, Symbiosis, Dysbiosis