Human microbiota - Wikipedia
In these mutualistic relationships, the hosts gain carbon and energy, and their microbes are Representation of the diversity of bacteria in the human intestine. Introduces beneficial and harmful relationships between humans and bacteria. Bacteria and humans have many important relationships. What Bacteria Can Tell Us About Human Evolution suggests a lengthy co- evolution between these types of bacteria, humans and our relatives. one day help us understand evolutionary relationships among species.
The human host and its microbial flora constitute a complex ecosystem whose equilibrium serves as a remarkable example of reciprocal adaptation. Normally, microbe is responsible for resistance to colonization by exogenous pathogenic microorganisms.
However, sometimes potential pathogenic bacteria come in close contact with the host and are responsible for opportunistic infections in immune-compromised hosts [ 3 ].
Some microbes that colonize in human are commensal that is they co-exist without harming human, whereas others have a mutualistic relationship with their human host that is both are beneficial to each other symbiotic approach.
Conversely, some non-pathogenic microbes can harm human host via the metabolites produced by them viz. Certain microbes perform specific tasks known to be useful to the human host. However, role of most resident microorganisms is not well understood. Moreover, based on evidences, now scientists are convinced that modern trends of diet, excessive use of antibiotics, obsession with cleanliness, caesarean deliveries etc.
This mini-review briefly describes about the microbes that are present in the human body under normal circumstances and do not cause any disease and are helpful to human in spending a healthy life.
Microbes on Skin Skin is the largest human organ which is the point of contact with the world. The most diverse populations of microbes present in human live on the skin. There are at least 1, different species of bacteria, fungi, viruses and other microbes which live on the skin. Most of which are harmless or even beneficial to human host.
Colonization on skin is highly variable depending on endogenous host factors, topographical location and exogenous environmental factors. Symbiotic microorganisms occupy a wide range of skin niches and protect against invasion by more pathogenic or harmful organisms. One example of bacteria that protects the skin is Bacillus subtilis.
It produces bacitracin on the skin, a toxin poison that helps it in fighting with other microbes. The property of bacitracin to act as an antibacterial agent has been exploited to use it as antibiotics. Skin microflora may also have a role in educating the billions of T cells, priming them to respond to similarly marked pathogen [ 4 ]. Primary bacterial colonizers are Staphylococcus epidermidis and other coagulase-negative Staphylococci. Other microorganisms that are generally regarded as skin colonizers are species of CorynebacteriumPropionibacterium and Brevibacterium.
The most commonly isolated fungal species is Malassezia sp. The Demodex mites viz. Demodex folliculorum and Demodex brevis are microscopic arthropods and these are also regarded as part of the normal skin flora [ 5 ]. Microbes in Nasal Cavity A little is known about the microbes in nasal cavity. However, evidences suggested that microbiota of the nasal cavity plays a crucial role in determining the reaction patterns of the mucosal and systemic immune system.
Different microbiota are found in different parts of the nasal cavity. Many studies are conducted to know about the microbiota of nasal cavity.
Role of Microbes in Human Health
The studies suggested absence of Gramnegative bacteria in nasal passage that are regularly present in pharynx. However, viridans type Streptococci are sparsely present in the nasal cavity.
On the other hand, species of CorynebacteriumAureobacteriumRhodococcus and Staphylococcus have been found to be present dominantly. These data suggested that microbiota present in of the nasal cavity of adult humans are strikingly different from that of the pharynx [ 6 ]. The anaerobic bacteria found were Propionibacterium acnes in The microorganisms found in the human oral cavity are called as the oral microflora, oral microbiota or oral microbiome.
This microflora comprises over species with distinct combination at different habitats. Most organisms that are colonizing are beneficial to human health but some microbes transit from a commensal relationship to pathogenicity.
Human and Bacteria Mutualism by Kelly Lee on Prezi
The reasons for the transition are not understood, however it is believed that it may be because of changes in the environment or personal hygiene [ 8 ]. Scientists have found the agonist as well as antagonist interactions between these microbes. For example, interaction between Streptococcus gordonii and Actinomyces naeslundii are both agonist and antagonist in nature. Both these microbes are involved in biofilm production. Conversely, hydrogen peroxide produced by S.
Another example of antagonist relationship is of Streptococcus mutanswhich is a leading cause of dental caries. It uses quorum sensing and releases bacteriocin when introduced to other bacteria while StreptococcusActinomycesand Lactobacillus generate an acidic pH, which results in inhibition of growth of a variety of bacterial species [ 1011 ].
Microbes in Human Gut The human gut serves two major functions: It digests food, absorbs nutrients, and assists with waste excretion. At the same time, intestine serves as house for enormous population of microbes that help in digestion and guard against pathogenic microbes.
The intestinal microbiota of newborns is characterized by low diversity and a relative dominance of the phyla Proteobacteria and Actinobacteria. There are also differences between the gut microbiota of formula-fed and breast-fed infants.
By the end of the first year of life, the microbial profile is distinct for each infant. The computational challenges for this type of analysis are greater than for single genomes, due the fact that usually metagenomes assemblers have poorer quality, and many recovered genes are non-complete or fragmented.
After the gene identification step, the data can be used to carry out a functional annotation by means of multiple alignment of the target genes against orthologs databases. The genetic region is characterized by a highly variable region which can confer detailed identification; it is delimited by conserved regions, which function as binding sites for primers used in PCR.
The technique is fast and not so expensive and enables to obtain a low-resolution classification of a microbial sample; it is optimal for samples that may be contaminated by host DNA. Primer affinity varies among all DNA sequences, which may result in biases during the amplification reaction; indeed, low-abundance samples are susceptible to overamplification errors, since the other contaminating microorganisms result to be over-represented in case of increasing the PCR cycles.
Therefore, the optimization of primer selection can help to decrease such errors, although it requires complete knowledge of the microorganisms present in the sample, and their relative abundances. The first thing to do in a marker gene amplicon analysis is to remove sequencing errors; a lot of sequencing platforms are very reliable, but most of the apparent sequence diversity is still due to errors during the sequencing process.
To reduce this phenomenon a first approach is to cluster sequences into Operational taxonomic unit OTUs: Another approach is Oligotypingwhich includes position-specific information from 16s rRNA sequencing to detect small nucleotide variations and from discriminating between closely related distinct taxa.
These methods give as an output a table of DNA sequences and counts of the different sequences per sample rather than OTU. Other popular analysis packages provide support for taxonomic classification using exact matches to reference databases and should provide greater specificity, but poor sensitivity.
Unclassified microorganism should be further checked for organelle sequences. Phylogenetic comparative methods PCS are based on the comparison of multiple traits among microorganisms; the principle is: Ancestral state reconstruction is used in microbiome studies to impute trait values for taxa whose traits are unknown.
Phylogenetic variables are chosen by researchers according to the type of study: All this methods are negatively affected by horizontal gene trasmission HGTsince it can generate errors and lead to the correlation of distant species.
There are different ways to reduce the negative impact of HGT: Skin and vaginal sites showed smaller diversity than the mouth and gut, these showing the greatest richness. The bacterial makeup for a given site on a body varies from person to person, not only in type, but also in abundance. Bacteria of the same species found throughout the mouth are of multiple subtypes, preferring to inhabit distinctly different locations in the mouth.
Even the enterotypes in the human gut, previously thought to be well understood, are from a broad spectrum of communities with blurred taxon boundaries. Firmicutes and Bacteroidetes dominate but there are also ProteobacteriaVerrumicrobiaActinobacteriaFusobacteria and Cyanobacteria.
If this is not removed by brushing, it hardens into calculus also called tartar. The same bacteria also secrete acids that dissolve tooth enamelcausing tooth decay.