The potential influences of Deepwater Horizon light Louisiana crude oil and oil dispersed by Corexit 9500 on human fecal microbiota were investigated in this study. We analyzed the shifts of bacterial communities and bacterial numbers from in vitro cultures of feces exposed to oil, dispersant, or dispersed oil using pyrosequencing and quantitative real-time PCR molecular approaches. Using the identical microbial communities in in vitro incubations of fecal suspensions treated with different concentrations of crude oil and dispersant provided us with comparative results for theconcentrations tested for each individual.
Dispersed oil affected the intestinal microbiota more than either oil or dispersant alone (). This may be due to the increased solubility of dispersed oil, which could provide more surface area of hydrophobic and toxic compounds for microbial contact than oil alone. Therefore, dispersed oil may be more bioavailable to the microbiota than oil alone. Previous studies reported that chemical dispersants may increase the concentration of PAHs in the water column (20
). The toxicity of dispersed oil showed that chemically dispersed oil increased the toxicity and concentrations of TPHs and PAHs in fish more than mechanically dispersed oil, dispersant alone, water-soluble oil fractions, or seawater alone (22
). In this study, significantly greater influences of dispersed oil on fecal bacteria than oil alone were shown at the genus and species levels (). Exposure to dispersed oil increased the abundance of E. coli
in all three individuals, while the abundance of B. uniformis
and uncultured Faecalibacterium
were reduced. The increased abundance of E. coli
could be an important health concern, because high densities of E. coli
have been associated with increased susceptibility to Salmonella enterica
). B. uniformis
, a prominent species in the intestinal microbiota, is correlated with host urinary metabolites, such as citrate and taurine (10
). The reduction of Bacteroidetes
by dispersed oil in fecal microbiota could affect barrier disruption with potential susceptibility to protection against pathogens. It is difficult to know the effect of uncultured Faecalibacterium
reduction in samples treated with dispersed oil, because of limited information on uncultured Faecalibacterium
. The most abundant Faecalibacterium
species in the human intestine is Faecalibacterium prausnitzii
, which is related to anti-inflammatory factors and reduced in patients with inflammatory bowel disease and Crohn’s disease (23
). Most species were more influenced by the oil-dispersant mixture than by the oil-alone treatment. The changes of bacterial population could change nutrient compositions that could affect other biological groups in the gastrointestinal tract, as in previous reports of microeukaryote shifts in mangrove sediments (25
). Although the concentration of oil-dispersant mixtures that significantly influenced microbiota was over the level of previously detected concentrations in seafood, the study provides a conservative estimate of impact on human intestinal microbiota with regard to potential food safety concerns (see Table S1 in the supplemental material).
In conclusion, our molecular, bioinformatic, and statistical results indicated that when comparing the toxicity of Deepwater Horizon crude oil alone, Corexit 9500 alone, and dispersant-oil mixtures, the human fecal microbiota was impacted more by dispersed oil than by either oil or dispersant alone, which were found not to be highly toxic. Although the results have the typical limitations of in vitro studies extrapolated to in vivo exposure and we used fecal samples representative of the lower gastrointestinal microbiota that show individual variation in microbial composition, this pilot study provides new information on the potential influences of oil and dispersed oil on the human intestinal microbiota. This topic should be further explored when assessing the potential risk of exposure to petrochemical contaminated food products.