Breast microbiota
The human microbiota is diverse with the human intestinal tract, a rich environment bustling with trillions of microbes. The colon is home to microbiota with concentrations of 1011–1012 cells/ml, which is the highest recorded for any microorganism habitat (Ley et al. 2006).
The microbiota of the breast differs from other body sites and research shows it contains both pathogenic and non-pathogenic bacteria (Urbaniak et al. 2012). Bacteria have been isolated from the lobules ducts and fatty tissues, and scientists have proposed that the breast microbiome could be beneficial because they contribute to maintaining a healthy breast tissue (Xuan et al. 2014).
The researchers showed that bacteria have been isolated from both lactating and non-lactating breast (Urbaniak et al. 2016). Major phyla identified by 16S pyrosequencing are Proteobacteria, Actinobacteria, Verrucomicrobia, Deinococcus-Thermu, Firmicutes, Bacteroidetes and Fusobacteria. The most abundant phyla in breast tissue were Proteobacteria followed by Firmicutes as shown in Fig. 2 (Xuan et al. 2014; Urbaniak et al. 2016).
The maintenance of an equilibrium between the microbiota and host is delicate and a change in this balance could have a negative effect on the individuals’ health leading to several disease conditions including cancer (Plottel and Blaser 2011).
Dysbiosis is a phenomenon that refers to the irregular distribution or dysfunction of the microbe community in a part of an organism. It occurs when the distribution of certain microbial species changes within the community and this hamper symbiotic relationships in the microbial community (Jones 2018).
Dysbiosis upsets the microbiome equilibrium and such disruption might encourage the deconjugation and re-utilising of oestrogen with a resultant upsurge of the individual's oestrogen levels. This will contribute to an increased risk of oestrogen facilitated cancer including breast cancer (Belkaid and Hand 2014). Dysbiosis has also been involved in increases in inflammation and inflammatory cytokines which is an indication of cancer (Shapira et al. 2013).
A comparison was made between the breast microbiota of tissues from ER + ve breast cancer subjects and healthy controls using 16S pyrosequencing technique. Out of the 1614 operational taxonomic units (OTS) identified, there was no significant variation in richness between the number of (OTUs) in both groups but there was a significant difference between the evenness of the microbiota community. Out of 1614, OTS detected, 11 were abundant in healthy breast tissues and three in breast tumour tissue. Bacteria belonging to the genus Sphingomonas and the specie Sphingomonas yanoikuyae was more abundant in the healthy breast tissues while in the breast tumour tissues, bacteria in the genus Methylobacterium was more abundant (Xuan et al. 2014).
Nipple aspirate fluid from breast cancer patients and healthy control subjects revealed differences between the OTUs between the two groups. Bacteria belonging to, the genus Alistipes was found only in breast cancer patients while the genus Sphingomonadaceae was more abundant in the healthy control than the breast cancer needle aspirate samples. Sequencing identified the specie to be Sphingobium yanoikuyae (Chen et al. 2019).
Free circulating DNA (cfDNA) was examined and compared in plasma samples of three breast cancer patients and healthy counterparts. The bacteria species frequently found were Acinetobacter and Mycobacterium, but in the breast cancer patients, the spp were diverse and more probable to present at high levels than the healthy counterparts. One of the breast cancer patients with multiple Sphingomonas species infections remains alive, while another patient with Pseudomonas mendocina and Pannonibacter phragmitetu passed away. The third breast cancer patient who has Acinetobacter johnsonii XBB1 like the healthy controls was seen to live a normal life (Huang et al. 2018).
Sphingomonas
Members of the Sphingomonadaceae family are known for their capacity to degrade aromatic hydrocarbons and polycyclic aromatic hydrocarbons (PAH). They are highly significant environmental pollutants because of their carcinogenic properties in the body (Inoue et al. 2008). PAHs are present and prevalent in the atmosphere mainly because of inadequate combustion of fossil fuels. Individuals are exposed to these hydrocarbons from various sources, especially environmental such as air pollution (Crouse et al. 2010). PAHs can be ingested orally through the consumption of grilled or smoked foods such as meat and fish, cigarette and tobacco smoking. Also, through the consumption of inadequately washed vegetables contaminated with soil (Maanen et al. 1994; Heisterkamp and van Veen 1997; Boström et al. 2002; Gaudet et al. 2013). Paths can get into the body through the skin using dermal products containing black rubber (Inoue et al. 2008).
PAHs have been established as human carcinogens in the lungs and previous research has shown that mammary tumours can be induced by PAH, but knowledge in this field is limited regarding its association with females (White et al. 2016).
Sphingomonadaceae can be found at several natural environment habitats including both aqueous and terrestrial habitats such as marine, desert sand, water and dumpsite. Its extensive distribution in the environment arises from its scope to use varied organic compounds, growth and survive under low-nutrient conditions. Characterised by their yellow/orange pigment, they are gram-negative aerobic, non-sporing bacilli (Feng et al. 2014).
They are chemoheterotrophic and contain glycosphingolipids in their cell envelopes instead of lipopolysaccharide. The genus is subdivided into four genera: Sphingomonas, Sphingopyxis, Sphingobium and Novosphingobium (Balkwill et al. 2003).
Members of the genus sphingomonad can degrade a wide variety of PAHs and related compounds. These sphingomonads such as Novosphingobium aromaticivorans strain F199, Sphingobium sp. strain P2 and Sphingobium yanoikuyae strain B1 were found to possess an exceptional set of genes for aromatic hydrocarbon degradation. Sphingomonads can degrade both low molecular and high molecular weight PAHS and the capability to degrade these compounds is thought to be related to their physiological characteristic. The unique glycosphingolipid cell wall is thought to play a role in the degradation of PAHs (Pinyakong et al. 2003).