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.