Foodborne Sources of Bacteria Associated With Human Obesity

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McElhany, Katherine Grace
bacterial load of foods; pyrosequencing; gut microbiota
thesis / dissertation description
Recently published research has suggested that the microbial ecology of the digestive system may play a role in obesity. Obese people have been shown to have a higher proportion of bacteria from the Firmicutes division and a lower proportion of bacteria from the Bacteroidetes division in their gut. The goal of this study was to characterize the microbial communities in specific foods using a combination of microbiology and metagenomic techniques. The ultimate goal of this project was to identify specific foods that may be introducing the Firmicutes and Bacteroidetes bacterial groups into the human gut. Nine commonly consumed foods, both natural and processed, were selected for this study and were purchased from a retail outlet in College Station, TX. These included wheat bread, whole milk, spinach, low-fat yogurt, medium cheddar cheese, 80/20 ground beef, salmon, banana, and skinless chicken breast samples. The food samples were plated on Tryptic Soy Agar (TSA) media to determine the aerobic and anaerobic bacterial loads and to isolate bacteria. The total microbial community was extracted from these food samples and the 16S rRNA gene sequences of the microbiome were PCR amplified. The PCR amplicons were sequenced using pyrosequencing and the metagenomic data was analyzed using bioinformatic approaches. The culture-based data suggests that there is a substantial bacterial load on some of the food items, ranging from as low as 5.9x102 CFU/gm to 2.8x106 CFU/gm. Results of the pyrosequencing data indicate that the cheese, ground beef, salmon, milk, and chicken breast contain significant amounts of Bacteroidetes and/or Firmicutes. The results of this study suggest that 1) foods harbor a variety of microbial populations including those that have been associated with human obesity and 2) the consumption of specific food types could be influencing the types of microorganisms inhabiting the human gut.