Introduction

Anaerobic bacteria are infrequent pulmonary pathogens, but they may cause serious complications, such as aspiration pneumonia, lung abscess, and empyema [1]. The major organisms identified in these infections are Bacteroides melaninogenicus, Fusobacterium nucleatum and anaerobic Streptococci [2].

Anaeroglobus geminates, first isolated and identified by Jean-Philippe Carlier in 2000, is a non-fermenting gram-negative coccus belonging to the family Veillonellaceae [3]. Anaeroglobus geminates is phylogenetically close to Megasphaera and Veillonella [3]. Infections caused by Megasphaera spp. and Veillonella spp. have been previously described; however, infection caused by Anaeroglobus geminates has not been reported [4, 5]. Herein, we report the first case of clinical Anaeroglobus geminates infection that presented as pneumonia with empyema.

Case report

A 39-year-old male who had stayed in the intensive care unit for 30 days was found with oral bleeding and swelling of the gingiva. He was initially admitted for acute stroke. Despite aggressive treatment, the patient remained comatose and underwent tracheostomy 3 weeks after admission in anticipation of long-term ventilator dependence.

During periodontal examination, generalized hyperplastic gingiva, bleeding on probing, and multiple dental caries were noted. Acute periodontitis was diagnosed. The oral surgeons removed microbial plaque and calculus. Regular brushing was suggested by the oral surgeon. Two days later, the patient developed respiratory distress and fever to 39.4 °C. Vital signs included a blood pressure of 120/100 mmHg, pulse of 89 beats per min; and a respiratory rate of 26 breaths per min. Crackles and rhonchi were noted over the right lower lung field. A chest X-ray (CXR) showed consolidation in the right lower lobe. Laboratory data revealed leukocytosis (white blood cell count 24.7 × 103/m3); renal and liver profiles remained in the normal range. Ventilator-associated pneumonia caused by aspiration was diagnosed. Piperacillin/tazobactam was initially administered intravenously (4.5 g every 6 h), and sputum specimens were collected for culture. Two days later, the fever persisted, and CXR revealed a large right-sided pleural effusion. Chest computed tomography (CT) also revealed a large right-sided pleural effusion and pleural thickening compatible with empyema (Fig. 1). A chest tube was inserted, and pleural fluid analysis revealed a pH of 5.34, glucose of 31 mg/dL, lactate dehydrogenase of 9,199 IU/L, and total protein of 3.9 g/dL. The sputum cultures failed to identify a pathogen. Gram stain of the purulent pleural fluid revealed gram-negative cocci. Two days after incubation, a pure culture of anaerobic bacteria was noted on CDC Anaerobe Laked Sheep Blood Agar (Becton-Dickinson and Company, USA). Colonies on the medium were round, grayish-white, non-pigmented, and non-hemolytic (Fig. 2). The isolate was further transferred to the Becton-Dickinson BBL Crystal Anaerobe ID system (BD Diagnostic Systems), a miniaturized identification method with modified conventional, fluorogenic and chromogenic substrates intended for the identification of anaerobic bacteria [6]. The isolate was initially identified as Veillonella spp but following 16S ribosomal RNA (16S rRNA) gene sequence analysis, the organism was confirmed as Anaeroglobus geminates [1]. Antimicrobial susceptibilities were determined by using agar dilution method. Agents tested included penicillin, clindamycin, chloramphenicol, piperacillin/tazobactam, ampicillin/sulbactam, and metronidazole. Susceptibilities to antimicrobials tested were interpreted according to Clinical and Laboratory Standards Institute (CLSI) criteria for anaerobes (2013). All the testing antimicrobial agents showed in vitro activity against Anaeroglobus geminates. We then continued piperacillin/tazobactam.

Fig. 1
figure 1

Thoracic computed tomography of the patient. Large amount of lobulated pleural effusion and thickening pleura in right chest region which indicates empyema (arrow)

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Fig. 2
figure 2

Colonies of Anaeroglobus geminates. The colonies of Anaeroglobus geminates isolated from the patient’s pleural fluid are smooth, grayish-white and round in shape ranging from 1 to 3 mm in diameter on CDC Anaerobe Laked Sheep Blood Agar (Becton-Dickinson and Company, USA)

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One week after the onset of pneumonia, the patient underwent surgical decortication for poor chest tube drainage. Operative findings revealed sticky pleural fluid, extending from the diaphragmatic pleura throughout the entire right lower lobe. Histology of the pleural tissues showed a picture of abscess with fibrotic change. His fever subsided soon after the surgical intervention. The patient became stable and successfully weaned off the ventilator 1 week later. After removal of the chest tube and completion of a 3-week course of antimicrobial therapy with piperacillin/tazobactam, he was transferred to a nursing home. Oral antibiotic treatment with clindamycin 2.4 g per day was prescribed for an additional week after transferring to the nursing home. Follow-up in the outpatient department showed no signs of recurrence.

Discussion

Anaeroglobus geminates was first isolated from suture anastomosis fluid in a 70-year-old woman after esophagojejunal anastomosis [3]. In addition to the gastrointestinal tract, Anaeroglobus geminates was also isolated from a human subgingival plaque [3, 7]. Jean-Philippe Carlier reported the isolates were unreactive in most conventional biochemical tests. Catalase activity and indole production were not detected. Nitrate reduction was negative, and lactate was not fermented [3].

According to the sequence analysis, Veillonella and Megasphaera spp. were the closest phylogenetic relatives of Anaeroglobus geminates in the family Veillonellaceae [3]. Megasphaera spp. has been shown to be a normal inhabitant in the human gastrointestinal tract and vagina and rarely cause infectious complications [5, 8]. Veillonella spp. is normal flora of the oral cavity, upper respiratory tract, small intestine, and vagina, which can cause meningitis, osteomyelitis, endocarditis, and pneumonia [4, 9–11]. The clinical impact and pathogenesis of Anaeroglobus geminates has not been previously described. This paper presents the first case report describing a serious clinical infection caused by Anaeroglobus geminates.

The isolate in our case was initially identified as Veillonella spp. according to the Becton-Dickinson BBL Crystal Anaerobe ID system. For detailed species identification, restriction fragment length polymorphism analysis by polymerase chain reaction (PCR)-amplified 16S rRNA gene was performed. The amplicon was sequenced and compared with the sequences in the GenBank database of the National Center for Biotechnology Information. The species was identified as Anaeroglobus geminates (99 % identity, 695/697, GenBank accession no. AM420054). This pathogen was initially misidentified as Veillonella spp. in the database of Becton-Dickinson BBL Crystal Anaerobe ID system because Anaeroglobus geminates was not in their database.

Cases of misidentification have been previously reported [12, 13].With the development of PCR and DNA sequencing, 16S rRNA gene sequencing has played an important role in the accurate identification of bacterial isolates and the discovery of novel bacteria, especially for bacteria that were phenotypically unusual, rare, slow-growing, and difficult to cultivate [14]. For pneumonia caused by anaerobic pathogens, it is difficult to establish the appropriate microbiologic diagnosis because the causative pathogen(s) is/are mostly contaminated by normal oral or pharyngeal flora, and many laboratories do not perform adequate anaerobic microbiological identification methods [15]. There is a possibility of bacterial misidentification by automatic identification systems, especially for rare bacteria, and 16S rRNA gene sequencing analysis in this condition is helpful.

The antibiogram of Anaeroglobus geminates in our case was susceptible to all antibiotics with an anaerobic spectrum, including penicillin, clindamycin, chloramphenicol, piperacillin/tazobactam, ampicillin/sulbactam, and metronidazole. Although all the antibiotics mentioned above were effective in vitro, our patient’s infection responded poorly to initial antibiotics (piperacillin/tazobactam) and tube drainage, at least until surgical intervention. The reason may be due to poor drainage of empyema, according to findings obtained during the decortications. Therefore, surgical intervention should be considered in patients with empyema that responds poorly to antibiotics and chest tube drainage [16, 17].

Conclusion

This case reported a severe infection caused by Anaeroglobus geminates, a genus in the family Veillonellaceae. Molecular identification by 16S rRNA gene sequencing analysis was helpful to accurately identify this rare pathogen. After diagnosis, the patient was successfully cured by the combination of effective antibiotics, surgical intervention, and adequate drainage.