Enterococcus hirae bacteremia associated with perinephric collection and renal abscesses in a diabetic woman

ABSTRACT Enterococcus hirae infection accounts for about 1% of all enterococcal infections. This number is likely to be underestimated because of inadequate identification. Human infection due to E. hirae is rarely reported. We present the case of a young woman with diabetes mellitus who developed symptoms of pyelonephritis and diabetic ketoacidosis. Renal computed tomography scan revealed the presence of subcapsular perinephric collection and renal abscesses. Her blood culture yielded E. hirae. Our patient was successfully treated with antimicrobials based on the susceptibility result. To our knowledge, this is the first reported case of perinephric collection and renal abscesses associated with E. hirae bacteremia.


INTRODUCTION
Enterococci are Gram-positive facultative anaerobic cocci that is rarely implicated in human disease. Enterococcus faecalis and Enterococcus faecium are the most prevalent species cultured from humans [1]. E. hirae, a species belonging to the Enterococcus is a zoonotic pathogen and rarely isolated from human infections [2]. Despite the rarity of E. hirae infection in humans, it is known to cause serious and life-threatening illness [3]. Clinicians need to be more aware of the clinical significance of this unusual pathogen.

CASE PRESENTATION
A 21-year-old woman with poorly controlled type 1 diabetes mellitus (HbA1c = 15%) presented with a three-day history of fever, dysuria, and f lank pain. She denied hematuria, urinary frequency, or urge incontinence. Physical examination revealed that the patient was alert, febrile, and hemodynamically stable. The oxygen saturation was 98% as measured by pulse oximeter while breathing ambient air. There was costovertebral angle tenderness on the left side. The remainder of the physical examination was unremarkable.
The patient was diagnosed with diabetic ketoacidosis (DKA) and concurrent f luid resuscitation and insulin therapy were instituted. DKA resolved within 24 h. However, the presence of fever, which is not a symptom of ketoacidosis, as well as loin pain and tenderness, prompted us to rule out renal or perinephric infection. Hence, a renal 4-phase computed tomography (CT) scan was performed, which revealed a left subcapsular perinephric collection measuring 1.9 × 4.7 × 9.1 cm, as well as multiple small renal abscesses at the upper and midpole of the left kidney, which coalesced with the subcapsular collection ( Fig. 1). Both kidneys were normal in size, and neither had a calculus, hydronephrosis, or hydroureter.
Percutaneous ultrasound-guided aspiration of the left perinephric collection was performed in which 10 cc of purulent material was aspirated. The patient was treated empirically with intravenous ceftriaxone 2 g once daily. After 5 days of incubation, the blood culture was positive for E. hirae, using the matrix-assisted laser desorption ionization time-of-f light mass spectrometry (MALDI-TOF MS) method. The blood culture isolate was susceptible to ampicillin, penicillin, and gentamicin, but cultures of the urine and purulent material were negative. Upon receipt of the blood culture result, the antibiotic was deescalated to intravenous ampicillin-sulbactam 3 g every 6 h after received 5 days of ceftriaxone. She showed marked clinical improvement in which the fever and f lank pain subsided as well as normalization of infective markers. The patient continued to receive intravenous ampicillin-sulbactam for a total duration of 6 weeks. A follow-up ultrasound scan after completion of antibiotic therapy revealed that the subcapsular perinephric collection and renal abscesses had completely resolved.

DISCUSSION
Enterococci are gram-positive, catalase-negative, non-sporeforming, facultative anaerobic bacteria. They are important opportunistic pathogens that are becoming more widely recognized as a major cause of community-acquired and nosocomial infections. To date, more than 50 enterococci species have been identified, with E. faecalis and E. faecium being the most commonly cultured from humans [4]. Infections caused by E. hirae are common in animals but human infections are relatively rare. Pyelonephritis, biliary tract infections and infective endocarditis due to E. hirae have previously been reported in humans [5][6][7][8].
E. hirae infection occurs more commonly among patients with diabetes mellitus, liver cirrhosis, and chronic kidney disease [5]. Our patient had poorly controlled diabetes mellitus which could have predisposed to urinary tract infection caused by E. hirae. There are several case reports on E. hirae causing urinary tract infection. Oh et al. reported a case of E. hirae urinary tract infection in an elderly man with benign prostate hyperplasia. The patient was found to have acute pyelonephritis and acute kidney injury [6]. Chan et al. reported the first case of E. hirae-related acute pyelonephritis with bacteremia in a Taiwanese woman [7]. To our knowledge, this is the first case of E. hirae bacteremia causing subcapsular perinephric collection and renal abscesses.
According to published reports, human infection with E. hirae is extremely rare, which could be due to the difficulty in isolating E. hirae from clinical specimens using standard diagnostic methods [9]. MALDI-TOF MS is a useful tool for identifying Enterococcus species from wild birds and distinguishing between similar Enterococcus species [10]. Before the advent of MALDI-TOF MS, E. hirae may be underdiagnosed due to limitations of the diagnostic methods.
In conclusion, we report the first case of perinephric abscess and renal abscesses associated with E. hirae bacteremia using MALDI-TOF MS. The number of reported cases of E. hirae is expected to rise as MALDI-TOF MS becomes more widely used, so clinicians should consider E. hirae as a causative pathogen for urinary tract infections in susceptible patients.

ABBREVIATIONS
DKA, Diabetic ketoacidosis CT, Computed tomography; MALDI-TOF MS, Matrix-assisted laser desorption/ionization-time of f light mass spectrometry