An unexpected opportunity can turn an old friend into a foe: septic arthritis caused by Neisseria macacea

Abstract Any patient presenting with acute, non-traumatic joint pain, swelling, and fever needs prompt evaluation and diagnosis for septic-type arthritis to enable effective treatment. Septic arthritis is primarily caused by bacteria and is frequently the most destructive form of acute arthritis, which requires rapid treatment. Although larger joints such as the hip and knee are more frequently affected, smaller joints such as the shoulder and ankle can also be affected. Septic arthritis is mostly caused by Neisseria gonorrhoeae and Staphylococcus aureus infections and usually affects only one joint. In this article, we present a case of septic arthritis in which Neisseria macacae was identified as the causative agent for the first time to our knowledge, in order to emphasize an underlying factor and microbiological differential diagnosis. The isolate was initially identified using Matrix-assisted laser desorption ionization–time-of-flight mass spectrometry (MALDI-TOF) and confirmed with Next Generation Sequencing. The primary objective of this report is to highlight that although Neisseria gonorrhoeae and Neisseria meningitidis are considered as pathogens, the other members of Neisseria species present in human and animal nasopharynx can cause opportunistic infections under favorable conditions. It is important to acknowledge the potential of these organisms to cause infections.