Normal flora: Definition, Types, its presence in our body sites, beneficial and harmful effects
Normal flora: Definition, Types, its presence in our body sites, beneficial and harmful effects
Normal Flora
In the normal, healthy person the gut flora is a balanced community of different organisms(Cambridge English Dictionary). Normal flora refers to the population of microorganisms that inhabit skin and mucous membranes of normal body. A healthy fetus in-utero is free from microorganisms. During birth the infant exposes to vaginal flora. Within few hours of birth, oral and nasopharyngeal flora develops and in a day or two resident flora of the lower intestine appears.
Types of normal flora
The normal microbial flora is more or less constant that is of two groups-resident flora and transient flora. Resistant flora consists of organisms which are regularly present in a particular area and when disturbed it re-establishes itself. e.g. Escherichia coli is a normal inhabitant of the intestine while transient consists of both non-pathogenic and potentially pathogenic bacteria that inhabit the body surface or mucous membrane for a limited period. They can eliminate from the body surface by mechanical means. Pathogens such as the pneumococcus and the meningococcus may find in nasopharynx of human from time to time.
Its presence in our body sites
Skin: Micrococcus species, Corynebacterium species, Staphylococcus epidermis
Mouth: bacteria of enterobacteriaceae family, Lactobacillus species, Staphylococcus epidermis, Staphylococcus aureus, Neisseria species, Corynebacterium species, Haemophilus species
Nose and nasopharynx: Neisseria species, Corynebacterium species, Staphylococcus aureus, Staphylococcus epidermis, Haemophilus species, Streptococcus pneumoniae
Conjunctiva: Neisseria species, Corynebacterium species, Staphylococcus epidermis, Haemophilus influenzae, Viridans streptococci
Large intestine and lower ileum: Staphylococcus species, Lactobacillus species, Clostridium species, Escherichia coli, Proteus species, Enterobacter aerogenes, Klebsiella pneumoniae, Pseudomonas aeruginosa, Mycoplsma species, Candida albicans, Streptococcus faecalis.
External ear: Corynebacterium species, Staphylococcus epidermis, Staphylococcus aureus.
Urethra: Candida species, Mycoplasma species, Mycobacterium smegmatis, Acinetobacter species
Vaginal(between puberty and menopause-Acid pH): Lactobacillus species, Streptococcus species, Clostridium species, Corynebacterium species, Gardenella vaginalis.
Before puberty and after menopause(alkaline pH): Staphylococcus epidermis, Micrococcus species, Enterobacter species,Corynebacterium species, Viridans streptococci.
Beneficial roles
1. They prevent or suppress the colonization/invasion of the body by pathogens.
2. The bacterial flora of the intestinal tract synthesize vitamins, especially K and several B vitamins.
3. Antibodies produced in response to commensals cross-react with pathogens having related or shared antigens and thus raise the overall immune status of the host against pathogens.
4. Colicins, produced by some organisms of normal flora, have a harmful effect on pathogens.
5. The endotoxins liberated by them may help the defence mechanism of the body by triggering the alternative complement pathway.
Harmful effects
1. They become pathogenic when the host resistance is lowered.
2. They may act as pathogens in tissue outside their normal habitat e.g. normal flora of the intestine may cause urinary tract infection.
3. Streptococcus mutans may cause dental caries.
4. Penicillinases producing organisms can aggravate infection by interfering with therapy.
5. Use of broad spectrum antibiotics, affects the normal flora by inhibiting sensitive bacteria and thereby allowing overgrowth of resistant bacteria.
6. Normal flora may cause confusion in diagnosis due to their ubiquitous presence in the body and their resemblance to some of the pathogens.