Periodontitis Culprit Aggregatibacter actinomycetemcomitans (image) Georgia Institute of Technology Share Print E-Mail Caption Bacteria behind acute periodontitis. Aggregatibacter actinomycetemcomitans most often lives peacefully in the mouth until circumstances lead it to become infectious. It forms flower-like colonies, here under a microscope sporting a colorful stain added by a researcher. Aa is gram-negative. Credit Derren Ready (2012) CIL:38942, CIL. Dataset. https://doi.org/doi:10.7295/W9CIL38942 Creative Commons license Usage Restrictions See credit, CC Share Print E-Mail 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.