The Human Nickel Microbiome and its relationship to Allergy and Overweight in Women

Introduction Nickel exposure usually presents as Allergic Contact Dermatitis. However, Nickel not only causes dermatitis, but an excess of dietary Nickel is reported to be responsible for overweight, metabolic disorders and imbalance of gut microflora. Objective The aim of study is to expand a preliminary reported evidence of the presence of Nickel-resistant bacteria isolated in human microbiome and further evaluate their association with nickel allergy and overweight in females, the gender mostly affected by Nickel exposure. Materials and Methods We collected stool samples from 11 lean female with a nickel allergy (BMI 25). 11 subjects not allergic to nickel served as control group. Stool cultures were supplemented with increasing concentrations of nickel sulphate (NiSO 4 ⋅6H 2 O) from 0.1mM up to 50 mM, in both aerobic and anaerobic conditions (culturomics -approach Lusi, 2017). Stool cultures not supplemented with nickel were used as controls. Identification of Nickel resistant bacteria was made by MALDI-TOF technology. Results In control subjects, 5 mM NiSO4 was the cut off for microbial growth. Conversely, gut bacteria continued to grow at concentration higher than 5 mM in allergic subjects. In particular, Nickel resistant bacteria able to tolerate 32 mM of NiSO4 was detected in 10% of lean allergic and 29% of overweight allergic females. Gut microbes able to grow in at extremely high NiSO4 concentration (50mM) could only be detected in overweight patients with a severe nickel allergy. At increasing NiSO4 concentration, allergic females, especially those with increased BMI, showed a progressive decrease of Enterobacteriaceae along with an increased presence of Lactobacillaceae , Bacillaceae and Clostridiaceae compared to control subjects. Major changes in microbial composition were noted at 50 mM of NiSO4 in overweight allergic females. Conclusion Overweight females with a nickel allergy harbor gut microbes highly resistant to nickel and the role of these bacterial strains must be further elucidated.