|February 1, 2009||CONTACT AUTHOR||ShareThis|
Victoria Bengualid1, Jayanthi Krishnaprakash2, Rexie Tan3, John Kittrick3, Judith Berger1
Coagulase negative staphylococcus (CoNS) includes many species, most of which are not pathogens. However, one species staphylococcus lugdunensis is known to cause virulent disease. We present a case of bacteremia with s. lugdunensis and describe a screening algorithm for identifying these pathogens in a real time setting.
A 55 year old cirrhotic patient was admitted with hypotension and a gastrointestinal bleed. He was afebrile, but his white blood cell count was elevated (15,000 cells/mm3). He was started on ceftriaxone and flagyl for presumed spontaneous bacterial peritonitis. Blood cultures were positive for CoNS which was felt to be a contaminants since the patient did not have any implanted prosthetic devices. On hospital day 4, the patient was still on pressor support to maintain his blood pressure. Repeat blood cultures were still positive for CoNS. Vancomycin was added. On hospital day 7 blood cultures became negative. The patient died three days later. Speciation of the CoNS showed S. lugdunensis sensitive to oxacillin.
CoNS comprise a heterogeneous group of 30 distinct species; they are normal inhabitants of the skin and mucus membranes1. The most commonly identified is staphylococcus epidermidis. CoNS are usually indolent and cause disease mostly in patients with prosthetic devices. Therefore blood cultures positive for CoNS, in patients without hardware, are usually considered a contaminant.
One type of CoNS that has been shown to be a virulent pathogen is staphylococcus lugdunensis. Numerous cases have linked it to skin and soft tissue infections and to endocarditis. S. lugdunensis endocarditis usually infects native valves, especially the mitral valve2-3. Prosthetic valves and pacemaker lead endocarditis have also been reported4. It is associated with a high rate of heart failure, ring abscesses and embolism, much like s. aureus. Half of the cases required cardiac surgery4.
Are all cases of bacteremias with s. lugdunensis of clinical significance? A study by
Zinkernagel5 identified all patients with positive blood cultures for s. lugdunensis over a 9 year period. Of the 28 bacteremic patients, 13 had community acquired endocarditis (54% had emboli, and 85% underwent surgery), 13 patients had a source that included a catheter or a foreign body (mostly nosocomial acquired in patients with multiple co-morbities), and two patients had unidentified sources of infection. In this study, 81% of community acquired s. lugdunensis bacteremia was associated with endocarditis. 10 of the 12 cases of nosocomial acquired bacteremias were in patients with catheters and did not result in any complications related to the bacteremia. In the case presented above the patient had a community acquired infection. Speciation of the CoNS would have alerted the physician to a potentially virulent pathogen. Appropriate antibiotics could have been started earlier, as well as a work-up to identify the source of the bacteremia.
In response to this case, we instituted a screening test for S. lugdunensis. All positive CoNS blood cultures are tested for pyrrolidonyl arylamidase (pyr test). The pyr test is negative for s. epidermidis and a majority of CoNS. It is positive in a few other CoNS of which s. lugdunensis is currently the only CoNS linked to significant disease. If the pyr test is positive suggesting s. lugdunensis, then microbiology will do a d-mannose and an ornithine decarboxylase test. Both are positive in s. lugdunensis. These tests require an extra 10 to 15 minutes of a technician’s time. The cost is an additional $17.93 if all three screening tests are used for one sample.
Speciation of coagulase negative staphylococcus in the setting of possible disease should become more routine. Strategies to identify potential virulent CoNS, are needed not only to alert the physician to a potential pathogen but also to help elucidate the spectrum of disease for specific species of CoNS.