Good Bugs Gone Bad (IMAGE) University of Pennsylvania School of Medicine Caption This is a color-enhanced tissue section from a healthy mouse that displays the presence of commensal bacteria (Alcaligenes species, purple) on the interior of a Peyer's patch (gut-associated lymphoid tissue) and overlaying intestinal epithelial cells (green). Credit Gregory Sonnenberg, Ph.D.; David Artis, Ph.D., Perelman School of Medicine University of Pennsylvania; <i>Science</i> Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.