Examples of the good and bad bacterial flora

A rich diversity of microbiota is vital for good health, but some bacteria are better than others.

THE GOOD (top group, listed clockwise from orange): Various strains of Bifidobacteria help regulate other bacteria, control immune responses to invading pathogens and assist in vitamin production; some types of Escherichia coli help produce Vitamin K, essential for blood clotting, and keep bad bacteria in check; Lactobacilli produce vitamins, boost immunity and protect against carcinogens.

THE BAD (lower group, clockwise from green): Enterococcus faecalis is a common cause of post-surgery infection; Campylobacter jejuni and Campylobacter coli are both associated with disease, usually spread through contaminated food; Clostridium difficile is most harmful after a course of antibiotics, when it is able to proliferate.