Infective endocarditis is caused by a wide variety of pathogens. Most commonly Staphylococcus spp and Streptococcus spp are identified, but new species are constantly being discovered.1Gemella species are small Gram-positive cocci that are a rare cause of endocarditis that have been increasingly reported since 1982.2 Over time, Gemella species have been implicated in approximately 35 reported cases of endocarditis up to the year 2004.3 However, the frequency of infections with Gemella may be underestimated because of difficulties in the identification and classification of the organism.4,5
We report a case of Gemella endocarditis that was treated surgically and review the cases presented in the literature.
A 50-year-old white male presented to the emergency department in respiratory distress. Three days before admission, he developed progressive shortness of breath, fever, and progressive cough with blood tinged sputum. He also experienced night sweats for 2 weeks before his admission. His medical history was significant for a positive tuberculin skin test 4 years before admission, where he had chest radiographs taken on a routine basis. His most recent chest radiograph was 7 months before admission and was negative for signs of acute tuberculosis. He was taking no routine medications before admission. He smoked a half a pack of cigarettes per day and denied illicit or intravenous drug use.
His vital signs on admission were the following: temperature, 98.6°F; blood pressure, 123/109 mm Hg; heart rate, 133 beats per minute; respiratory rate, 27 breaths per minute. Physical examination revealed course breath sounds in the lungs bilaterally, with diffuse rhonchi. Auscultation of the heart was negative for murmurs. His dentition was poor, but no peripheral skin lesions were noted. The remainder of his physical examination was unremarkable.
A comprehensive metabolic profile, complete blood cell count, brain natriuretic peptide, erythrocyte sedimentation rate, troponin, urinalysis, urine drug screen, blood cultures, sputum culture, and chest radiograph were ordered on admission. Of these results, abnormal values were reported for white blood cell count (22.1 × 103/μL; range, 4.0-10.5 × 103/μL; with 11% bands), hemoglobin (10.5 g/dL; range, 11.7-14.9 g/dL), hematocrit (32.2%; range, 34%-46%), brain natriuretic peptide (333 pg/mL; range, 0-100 pg/mL), troponin I (0.43 ng/mL; range, 0-0.05 ng/mL), and erythrocyte sedimentation rate (20 mm/h; range, 10-20 mm/h). The urine drug screen was positive for cocaine, and the chest radiograph revealed bilateral dense infiltrates in the left mid lung and the middle and lower lung fields. He was admitted to the intensive care unit and started on broad-spectrum antibiotics, including piperacillin/tazobactam 4.5 g every 6 hours and levofloxacin 750 mg every 24 hours.
On day 2 of admission, the patient developed progressive respiratory distress and required intubation. He also developed left-sided hemiplegia, left-sided facial droop, and a new-onset 4/6 systolic heart murmur. Sputum cultures were positive on day 3 for Moraxella catarrhalis that was β-lactamase positive. Blood cultures were positive in 4 sets on day 3 for Gram-positive cocci and were eventually identified several days later as Gemella species by Vitek (bioMérieux, Durham, NC). The samples were sent to a reference laboratory for confirmation by API 20 strep (bioMérieux).
A computed tomography scan of the head was obtained to evaluate his hemiplegia and revealed that the patient has a large right-sided temporal/parietal ischemic infarct without hemorrhage. A transesophageal echocardiogram was performed and showed severe mitral valve regurgitation, perforation of the anterior mitral valve leaflet, and vegetations on the mitral valve (Fig. 1). The patient was diagnosed with endocarditis, and vancomycin 1 g every 12 hours and gentamicin 60 mg every 8 hours were added to his antibiotic regimen. Cardiothoracic surgery was also consulted to evaluate possible valve replacement.
Eight days after admission, the patient's condition continued to decline, and he developed cardiogenic shock due to severe mitral regurgitation. The risks and benefits of surgery, including the risk of cerebral hemorrhage in light of his acute ischemic stroke, were discussed with the patient and his family, and they wished to proceed with a valve replacement. He underwent a mitral valve replacement with a porcine valve to minimize the need for anticoagulation. The mitral valve was sent for pathology and was positive for tiny Gram-positive cocci (Fig. 2). The organism characteristics were consistent with those of the Gemella species in his blood cultures.
The patient improved markedly after surgery and was transferred to the general medical floor 6 days later. However, approximately 10 days postoperatively, he developed an intracranial hemorrhage in the distribution of his previous infarct. A cerebral angiogram revealed a 1.3-cm mycotic aneurysm of the right middle cerebral artery. His condition continued to decline, and he expired.
Gemella spp were first described in 1917 as anaerobic, catalase-negative, Gram-positive cocci.6 When examined microscopically, these organisms appear as clusters in tetrads, short chains, or in pairs.3 The organisms are found on mucus membranes in humans, including the oropharynx, gastrointestinal tract, and genitourinary tract.3,5 Risk factors for infection with Gemella spp include dental disease and underlying heart disease, and there are reported cases of infection associated with intravenous drug use and gastrointestinal procedures.2,6,7
Gemella spp are easily decolorized during the Gram-staining process, and as a result, the Gram stain characteristics are highly variable.5,7-10 The organism's cell wall chemical composition of peptidoglycan is consistent with Gram-positive organisms.10 These characteristics have contributed greatly to the classification confusion surrounding these organisms. Because of this, the species of Gemella have been reclassified several times since they were first recognized as a human pathogen. Gemella morbillorum was formally known as Neisseria and Streptococcus.7 In 1988, the genus was officially transferred from Streptococcus to Gemella as a result of genetic analysis and its physiologic properties.11 As a result of these similarities, these organisms are frequently mistaken for different Streptococcus spp.5 The 4 species of Gemella that have implicated in human infections are G. moribillorum, G. haemolysans, G. bergeriae, and G. sanguinis.3
Case reports describing Gemella spp infections were first reported in 1978, and since that time the infection has been rarely identified.10 Since that time and up to 2004, approximately 35 cases of endocarditis have been reported in the literature. Of these cases, 15 were G. morbillorum, 14 were G. haemolysans, 4 were G. bergeriae, and 2 were G. sanguinis.3 One study of 52 cases of Streptococcus spp endocarditis, Gemella spp were identified in 5% of isolates and also made up 6% of the organisms misidentified as viridans group streptococcal species.5,8,12 Another analysis determined that Gemella spp made up 0.7% of all the cases of alpha-hemolytic streptococcal species other than S. pneumoniae that were analyzed.13
Identifying an infection with Gemella spp can be difficult. Standard identification techniques have varying success in identifying these organisms. Rapid phenotypic strains are often unable to accurately identify all strains in this species.8,13 In a study by Woo et al, the Vitek system failed to identify known Gemella isolates accurately.13 The ATB expression system (bioMérieux) did only slightly better and was able to identify 1 of the 2 Gemella species used.13 In our case, only the genus of the organism was able to be identified and not the exact species. A new identification method is the 16S rRNA gene sequence identification. The 16S rRNA gene is highly conserved in species of the same genus and may be the appropriate modality to identify these organisms.13
In our case, the patient needed to be treated aggressively because of the rapidly progressing and destructive nature of the infection. In several reported cases, severe regurgitation of the involved cardiac valve was reported in the majority of patients.3,6,8-11 Therefore, in addition to aggressive antibiotic therapy, surgery may be indicated as an early option in the treatment plan. Surgical intervention with cardiac valve replacement was performed in approximately one third of the cases reported in the literature.6,8,10,12
Antimicrobial treatment of infective endocarditis with Gemella spp is similar to that of other Streptococcus spp infections.14 In vitro antimicrobial susceptibility testing indicates that Gemella spp are sensitive to penicillin G and ampicillin.5 Synergistic activity between penicillin G and the aminoglycosides is also demonstrated.5 A combination of penicillin G and gentamicin is the current treatment of choice for these infections, and vancomycin is indicated in patients with penicillin allergy.5,7
Infective endocarditis with Gemella spp is rare. The bacteria are normally found on mucosal membranes in humans but have the potential to cause a devastating infection. The most common risk factors are poor dental hygiene, structural heart lesions, and intravenous drug use. The organisms are difficult to identify, and therefore, their true prevalence may be underreported. The 16S rRNA identification method appears to be the most accurate diagnostic modality, but it is not widely available yet. This infection, like any other case of endocarditis, should be treated aggressively to avoid serious complications, such as that observed in this case.
The authors thank Dr Philip Riley, DO, cardiology fellow, Tulsa Regional Medical Center, for his assistance with the transesophageal echocardiogram figures.
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