Nearly half of the 90 beverages from soda fountain machines in one area in Virginia tested positive for coliform bacteria -- which could indicate possible fecal contamination, according to a study published in the January issue of International Journal of Food Microbiology.

CNN: Soda fountains contained fecal bacteria, study found

There is evidence from other studies that good gut bacteria support positive mood too in part because of their effect on the vagus nerve and suggestions that antibiotics dampen this effect.

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They tested their treated materials with Staphylococcus aureus and Escherichia coli, the gram-positive and gram-negative bacteria that are always giving humans a bad day.

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Scientists divide bacteria into so-called "gram positive" varieties like Strep, which lack rigid cell walls and can be stained with dye, and "gram negative" ones that have cell walls and aren't dyeable.

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