Nedim Cekmen, *Oben Baysan, Emine Disbudak, Ceren Gunt
Intensive Care Unit, *Cardiology Department, Guven Hospital, Ankara, Turkey

Abstract

Background: Streptococcus alactolyticus is a rarely isolated bacterium, which classified under DNA cluster IV of the S. Bovis/S. equinus complex. Infections, especially infective endocarditis, caused by Strep. alactolyticus are very rare in humans.

Case Report: We describe a case of Strepotoccocus alactolyticus bacteriemia complicated by infective endocarditis. A 64-year-old male with a previous history of coronary artery bypass grafting applied to our cardiology outpatient clinic with complaints of dyspnea, fever, confusion and an apical holosystolic murmur. He was admitted to the intensive care unit. Transthoracic and transesophageal echocardiography showed the presence vegetation on the aortic valve. S. alactolyticus was detected on serial blood cultures. The patient was first treated with intensive antimicrobial therapy, and then underwent mitral and aortic valve replacements with uneventful follow-up.

Conclusion: Streptococcus alactolyticus infective endocarditis has only been reported previously in one patient. More information is certainly needed for diagnosis and treatment of patients infected with Streptococcus alactolyticus.

Key words: Streptococcus alactolyticus, endocarditis

Streptococcus alactolyticus is a particular subspecies grouped under streptococcal bovis/Streptococcal equinus complex (SBSEC) (1, 2). This complex contains non-beta hemolytic streptococcus and Lancefield group D streptococci. They are commensal colonizers of human and animal gastrointestinal tract and act as opportunistic pathogens (3).

S. alactolyticus has been isolated from intestinal flora of pigs, chicken, cows, pigeons and dogs (4, 5). Human infections caused by S. alactolyticus are extremely rare. Herein, we describe a rare case of bacterial infective endocarditis (IE) caused by S. alactolyticus.

Case report

A 64-year-old male was transferred to our emergency service by his family with difficulty of breathing, tachycardia, fever and confusion. He had previous history of coronary artery bypass graft surgery one month before. On admission, his vital signs were as follows high respiratory rate (32 breaths/min), temperature 38.6 C°, blood pressure 150/90 mmHg, heart rate 132 beats/min, and SpO₂ 67 %. He was urgently transferred to the intensive care unit (ICU). He had diminished respiratory sounds with crepitating rales bilaterally. We detected a grade 3/6 an apical holosystolic murmur on his left precordium. Glasgow coma score was 9, Acute Physiology and Chronic Health Evaluation score (APACHE II) was 18 and his Multiple Organ Dysfunction Score (MODS) was 6. Arterial blood gas analysis showed metabolic acidosis and hypoxemia: (bicarbonate 17.2 mmol/L, pH 7.14, PaCO₂ 35 mm Hg, and PaO₂ 47 mm Hg while on nasal oxygen at 6 L/min).

Blood cultures were taken. He was intubated and mechanically ventilated. Laboratory analyses showed high leukocyte count (23.400/L) with neutrophil dominance (83%), erythrocyte sedimentation rate 62 mm/h, C-reactive protein 135 mg/L (reference range: 0-5 mg/L) , procalcitonin 2.4 ng/L, and creatinine 1.4 mg/dL Immediate bedside transthoracic echocardiography revealed a suspicious mass on the aortic valve with severe aortic regurgitation. There was also a moderate degree mitral regurgitation. Same day urgent transesophageal echocardiogram (TEE) confirmed presence of a large mobile vegetation (23x15 mm) on aortic valve associated with severe aortic regurgitation (Fig. 1 and 2) and moderate degree mitral regurgitation (Fig. 3).  Empiric antimicrobial therapy with vancomycin, gentamicin, and penicillin G was initiated. His general condition showed a noticeable improvement within 48 hours. The group D streptococci were identified from blood cultures as S. alactolyticus by Vitek 2 (bioMerieux Vitek, Inc, Hazelwood, St. Louis, MO, USA). It was susceptible to penicillin. The second set of blood cultures were also positive for S. alactolyticus. Vancomycin was discontinued and intravenous penicillin G (3. 000.000 U every 4 hr) and gentamicin (63 mg every 8 hr) were continued. With that therapy, he showed persistent clinical improvement. His subsequent blood cultures were negative. The patient was extubated on the 10^th day of his intubation. The neurologist’s consultation including brain magnetic resonance  imaging (MRI) was unremarkable for the presence of cerebral embolism. We recommended to the patient early surgical intervention. He agreed with the proposal and underwent valvular heart surgery with bioprosthetic aortic and mitral valve replacements. Based on the S. alactolyticus sensitivities, antimicrobial therapy was deescalated to ceftriaxone, which was planned to continue for another six-weeks. The patient recovered completely and was discharged on the 44^th day of hospitalization. He was well on follow-up 8 weeks after discharge. He was also informed about an outpatient gastroenterology consultation for possible colonoscopy procedure.

Figure 1. A large aortic valve vegetation on TEE image (Mid esophageal 134 degree)

TEE- transesophageal echocardiography

Figure 2. Severe aortic regurgitation caused by infective endocarditis.

Figure 3. Moderate mitral regurgitation