Native Valve Infective Endocarditis Caused by Dual Infection of Staphylococcus aureus and Pseudomonas monteilii: A Case Report

Infective endocarditis (IE) is most commonly associated with Gram-positive bacteria such as <i>Staphylococcus aureus</i>. Gram-negative causes are less common, and are typically associated with pacemakers, prosthetic valves or intravenous drug use. <i>Pseudomonas monteilii</i> is an environmental organism that is rarely reported in human infection, with its presence in sputum often regarded as colonisation or contamination. This case describes a 30-year-old man with no underlying structural heart disease who was found to have a 6-8mm mitral valve vegetation on echocardiography. His blood cultures grew <i>Staphylococcus aureus,</i> whilst his sputum cultures grew <i>Pseudomonas monteilii</i>. This represents the first documented case of native valve infective endocarditis caused by both <i>Staphylococcus aureus</i> and <i>Pseudomonas monteilii</i>. This case highlights the diagnostic challenges associated with atypical organism growth and highlights the need to integrate imaging and microbiological findings within the clinical context when uncommon organisms are detected. Ultimately, this rare case broadens the recognised microbiological spectrum of infective endocarditis and supports a high index of suspicion, early imaging, repeat investigation, and multidisciplinary care to achieve good outcomes.