Comamonas kerstersii is a non-fermenting Gram-negative bacillus. It has been associated with intra-abdominal infections. We describe a clinical case of bacteremia caused by C. kerstersii in a young man with acute appendicitis. The first identification, using the Vitek2 compact system (BioMerieux) from blood cultures, was Comamonas testosteroni. However, using MALDI-TOF was identified as C. kerstersii. The patient was treated first with ampicillin sulbactam and then piperacillin tazobactam with favorable evolution. Within the genus Comamonas, C. testosteroni has been the most frequently reported species as a cause of infections in humans, only 23 cases of C. kerstersii being described. Given the problems of phenotypic identification of these microorganisms, it is possible that some C. testosteroni reports could have corresponded to C. kerstersii. This case highlights the pathogenic role of C. kerstersii and the importance of using MALDI-TOF as a diagnostic tool for non-fermenting Gram-negative bacilli identification.