Discussion:
K. oxytoca  endocarditis is an uncommon entity that can infrequently cause endocarditis and is associated with poor outcome. In comparison to more virulent organisms like Staphylococci , gram-negative bacteria have a lower tendency to infect native heart valves due to their reduced ability to adhere to the endocardium.4 However, Klebsiella species endocarditis are responsible for high rates of complications and mortality. 2 We report a case of K. oxytoca  endocarditis in an elderly man who presented with heart failure and severe aortic stenosis secondary to infective endocarditis.
K. oxytoca bacteremia is commonly seen in the setting of hepatobiliary tract, urinary tract, skin and soft tissue, and peritoneal infection. 2,5 The documented pathways through which K. oxytoca enters the bloodstream in cases of bacteremia are ranked in descending order as follows: the hepatobiliary tract (50%-55%), intravascular or urinary catheters (7%-16%), the urinary tract (5%-6%), skin and soft tissues (3%-5%), and the peritoneal cavity (2%-6%). Moreover, in 23% to 34% of infections, the specific entry points remain unidentified.6,7Although our patient didn’t have any history of immunosuppression, he had other risk factors for developing gram-negative infective endocarditis including his advanced age and history of recent prolonged hospitalization for septic shock secondary to K. oxytocabacteremia of urinary source.
It is well known that echocardiography is the mainstay of cardiac imaging for diagnosis of infective endocarditis.8Transesophageal echocardiography (TEE) is a more sensitive test compared to transthoracic echocardiogram (TTE) which is generally the first diagnostic test for patients with suspected infective endocarditis. In addition, TEE is superior to TTE for detection of cardiac complications including abscess, leaflet perforation, and aortic pseudoaneurysm or intracardiac fistula. 9,10 As in our patient, early complications were better visualized on TEE, and the surgical intervention followed soon after. Given the high morbidity and mortality rates associated with these infections, timely surgical consultation is of paramount importance. 11
Similarly, microbiological diagnosis of infective endocarditis is primarily based on blood culture, excised cardiac valve tissue, or infected emboli. This conventional approach has been shown to be successful in 92 to 95% of cases in which a microorganism is present.11 In regard to our patient, a chronic vegetation at the base of the right coronary cusp with fibrosis of the left ventricular outflow tract was found on histopathological analysis confirming the diagnosis of infective endocarditis as per modified Duke’s criteria. Although, the conventional microbiological analysis of cardiac valve tissue was unremarkable, K. oxytoca  specific DNA was detected on a broad-range polymerase chain reaction technique of affected valve/tissue.
The patient in our case report had no history of intravenous drug use, nor he had any exposure to animal farms, or any active exposure to pet animals. Culture negative endocarditis due to fastidious organisms was initially considered among the differential diagnoses, however serological titer tests and automated testing of blood cultures, in addition to the use of specialized culture media (enriched broth) were unremarkable. This also highlights the fact that molecular based techniques could potentially be helpful for the identification and analysis of this life-threatening infection.
The most effective drugs against these microorganisms include third generation cephalosporins and aminoglycosides, which are generally administered together. While the ideal period for treatment is not clearly established, a recommended duration of around 6 weeks is advisable. Additional antibiotics like imipenem, aztreonam, and fluoroquinolones have also shown effectiveness against gram-negative bacteria. 12 Our patient showed clinical improvement with a four-week course of intravenous ceftriaxone.