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That Troublesome Enterococcus
Abstract & Commentary
By John F. Joseph, MD, FACP, FIDSA, FSHEA, Associate Chief of Staff for Education, Ralph H. Johnson Veterans Administration Medical Center; Professor of Medicine, Medical University of South Carolina, Charleston, SC, is Associate Editor for Infectious Disease Alert.
Dr. John is a consultant for Cubist, Genzyme, and bioMerieux, and is on the speaker's bureau for Cubist, GSK, Merck, Bayer, and Wyeth.
Sources: Grupper M, et al. Enterococcal-associated lower respiratory tract infections: a case report and literature review. Infection. 200937:60-64; Bergman R, et al. Pleural Enterococcus faecalis empyema: an unusual case. Infection. 200937:56-59.
Enterococcus used to be considered the caboose of pathogens; maybe it mattered, but it still was at the far rear. Times have changed, and the enterococcus has taken more prominence as a pathogen, particularly in nosocomial infection. Yet, in regard to pneumonia and pleural disease, it ranks far at the bottom still. In fact, some would regard its causation in pneumonia as rare.
Grupper et al from Haifa, Israel, report a case of enterococcal bacteremia apparently caused by a lower respiratory tract infection in an 81-year-old man. The patient had undergone multiple urologic procedures and resided in a nursing home. He had a ureteral stent and needed a percutaneous nephrostomy. Many antibiotic courses preceded the current admission for pneumonia. His blood culture grew E. faecalis susceptible to penicillin and vancomycin but highly resistant to gentamicin. The sputum also grew E. faecalis with the same antibiogram. He was treated with intravenous ampicillin and did well.
Because of the rarity of the microbiologic findings in this case, Grupper et al reviewed the literature on the topic of enterococcal pneumonia. They found nine cases, with three caused by E. faecium. Two of the patients died; only three cases were nosocomial. Complications included lung abscess in two and septic shock in two. Penicillin resistance was common. Three of the patients had no underlying disease.
Grupper et al agree that the condition is rarely described, but they do not succumb to the idea that the rare reporting of enterococcal pneumonia accurately describes the epidemiology. They argue that the findings in their patients are very similar to pneumonia caused by more common respiratory pathogens. They also note that the enterococcus colonizes the upper airway as frequently as its bacterial counterparts. Finally, the tedium in identifying all those bacteria that seem to be normal flora surely underestimates how frequently enterococci may be in pathologic sputum.
In another unusual enterococcal case, E. faecalis was proven as a cause of empyema in a 63-year-old lady admitted with stroke and septic shock to a Dutch hospital in Ede, The Netherlands. The pleural fluid had only 291 cells but had a protein of 22.5 g/L. A chest tube was needed to drain the pus. Two other loculated areas developed during therapy, found during the initial chest tube drainage. Treatment with amoxicillin and clavulanic acid eventually, over five weeks of therapy, allowed resolution of the empyema and reversal of the septic shock.
These cases and reviews raise the specter of an ever-evolving spectrum of disease due to enterococcus. This genus is certainly no longer an innocent bystander, though these cases highlight that in some organ systems, like the lung, their pathogenicity is not well recognized. I like to think of enterococcus as a weakened hemolytic streptococcus. In fact, we once referred to the group by their Lancefield designation as a Group D streptococcus. But we have come a long way since the early classification by Rebecca Lancefield: Enterococcus now holds a premier seat as the maestro of antibiotic resistance, both inherent and acquired, and newer studies are recognizing more virulence mechanisms, some of which have an association with its antibiotic resistance (Clin Microbiol Rev. 2000:13:513-522).
These current reports also highlight the need to be vigilant about isolating enterococcus from otherwise sterile fluid, or when seeing enterococcal bacteremia without a common focus like the endocardium or the urinary tract. The key is to regard isolation of an enterococcus, particularly the species E. faecalis, as a pathogen until shown clinically that it is not. Having made that admission, the clinician's job is far from over, since the problem of eradicating the organism may not be simple and the use of synergistically bactericidal combinations may be necessary for cure.
Clearly, in this 200th year since Darwin's birth, indeed an age of recognizing evolution, particularly in bacteria as a driving force in medicine, we can look to the lowly enterococcus as the great demonstrator of the impact of antibiotic exposure in the selection of the fittest.