Pneumonia due to Stomatococcus mucilaginosus in an AIDS patient: case report and literature review

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Stomatococcus mucilaginosus is a normal inhabitant of the mouth, throat and upper respiratory tract. It is a Gram-positive coccus closely related to the genus Rothia [1]. Since the first case in 1978, its involvement has been reported in an increasing spectrum of infections, exclusively among immunocompromised patients. We report a case of pneumonia in an AIDS patient and review the 69 published cases of infection due to this pathogen.

A 43-year-old man was admitted for subacute dyspnea. He was a heavy smoker. A positive serology for HIV had been discovered in 1989. He had genital tuberculosis in 1990, pneumocystis pneumonia in 1995 (with cutaneous allergy to co-trimoxazole), and cerebral toxoplasmosis in June 1996. His medications were penta-midine aerosol, pyrimethamine, clindamycin, indinavir, stavudine, and lamivudine.

In December 1996, the patient began to complain of mild dyspnea, which became worse in the first days of 1997, accompanied by a productive cough. The patient was admitted in January. On examination, he was polypneic (respiration rate: 40/min) with orthopnea, audible bronchospasm with bilateral symmetric sibilants, ronchi, and some crackles in the two bases. His temperature was 37.2°C, his pulse was 100/min, and his blood pressure was 130/70 mmHg. The chest X-ray showed a sequellar reticular pattern in the middle lobe. The arterial blood partial pressure of oxygen was 70 mmHg, the carbon dioxide level was 30.5 mmHg. pH 7.4, and the bicarbonate level was 21 mmol/L. The white cell count was 6300/mm3, the neutrophil count was 4200/mm3, the CD4+ lymphocyte count was 50/mm3 (6%), the platelet count was 210 000/mm3, and the hemoglobin level was 13.3 g/dL. The C-reactive protein level was 212 mg/L. The other laboratory values were normal. On admission, pneumocystis pneumonia due to prophylaxis failure was suspected. Intravenous trimethoprim-sulfamethoxazole and methyl-prednisolone were started with aerosolized salbutamol. As the patient's condition did not improve, a fibro-bronchoscopic examination was performed on the fourth day. It showed purulent secretions from the entire bronchial tract. The bronchoalveolar lavage showed 8.1x106 cells/mL with 85% neutrophils, no acid-fast bacilli, no pneumocystis, and negative im-munofluorescence for Legionella. Gram-stained smears showed numerous Gram-positive cocci in clumps. After bronchoscopic examination, trimethoprim-sulfamethoxazole was empirically replaced by amoxy-cillin plus clavulanic acid (3g/day). The patient's condition improved quickly in 4 days. S. mucilaginosus grew in pure culture (105 CFU/mL) in the endotracheal aspirates and in the bronchoalveolar lavage. It was characterized by strong adherence to the agar and was catalase negative. A high production of slime was observed. The antibiogram (disk diffusion method) showed resistance to macrolides and quinolones, and sensitivity to aminoglycosides, rifampicin, fosfomycin, and glycopeptides. The penicillin MIC was 8 mg/L and that of trimethoprim-sulfamethoxazole was > 8 mg/L. All the specimens of blood cultures were negative for mycobacteria. Cryptococcal antigenemia results were negative and so were the results of the search for cytomegalovirus. The serologic tests for chlamydiae, Mycoplasma, Legionella, rickettsiae, influenza virus, parainfluenza virus, syncytial respiratory virus and adenovirus were negative.

The clinical spectrum of S. mucilaginosus infections is expanding. Sixty-nine cases (Table 1) have been recorded with 21 in children. Fifty-eight per cent are bacteremias. Almost all cases occur in conjunction with a severe underlying disease as shown in Table 1, mainly leukemia, bone marrow transplantation, and solid cancers. Three main predisposing conditions are found: neutropenia due to drug toxicity (defined as less than 1000/mm3 neutrophils), central venous catheter, and mucosal ulcerations.

Table 1. Infections due to Stomatococcus mucilaginosus: clinical presentation, main underlying diseases and predisposing conditions [4–14]
   Underlying diseasePredisposing conditions
 Number of casesFatal outcomeLeukemiaBMTSolid tumorsOthersNeutropeniaCVCMucitisOthers
  1. BMT, bone marrow transplantation; CVC, central venous catheter; IVDU, intravenous drug user.

  2. a Two chronic ambulatory peritoneal dialysis peritonitis, empyema, cellulitis around a Broviac catheter, nosocomial endophthalmitis, osteomyelitis, cholangitis. The last two cases occurred without immunodepression [9,10].

Bacteremias4031759AIDS 2242311IVDU 2
      Diabetes 2 Catheterrelated 7Dental surgery 2
Meningitis84331 762 
Endocarditis71  Heart valvular abnormalities 4  IVDU 4
      Valvular prosthesis 4    
Pneumonias70211AIDS 2442 
Miscellaneousa701Dialysis 211 
Total698221011363415 

These predisposing factors are a consequence of the properties of Stomatococcus. Since this organism belongs to the oral flora, oral ulcerations are a portal of entry, especially if neutropenia develops. This is in agreement with previous studies which recorded an increasing incidence of Gram-positive cocci in bacteremias among hematologic patients treated with aplastic chemotherapies [2]. The strong adhesive qualities of Stomatococcus [3] may predispose its engraftment on defective heart valves or prostheses. One hypothesis for the origin of Stomatococcus in endocarditis is the tendency of drug users to lick the needle, so as not to lose any drug, or to stick themselves in the mouth.

Four S. mucilaginosus infections have been reported in AIDS patients: two bacteremias [4,5] and two pneumonias [5,6]. We report a third case of pneumonia. In the three cases of pneumonia in AIDS patients, Stomatococcus was isolated from the lungs (bronchoalveolar lavage). In immunocompromised patients, with impaired bronchial immunity, Stomatococcus, found in bronchial secretions [3], can easily invade the parenchyma. Moreover, AIDS patients often have oral ulcerations. In all AIDS patients, CD4+ lymphocyte counts were lower than 100/mm3. Although rare, Stomatococcus has become an opportunistic pathogen in HIV-positive and other immunocompromised patients.

β-Lactams were used in 43 of the reported cases and vancomycin in 35 cases. Strains with diminished susceptibility to penicillin (from 0.25 to 1 mg/L) have sometimes been isolated [7]. Moreover, the strains isolated in AIDS patients who had previously received co-trimoxazole as prophylaxis for pneumocystis have diminished susceptibility to this antibiotic, although Stomatococcus is usually sensitive [4,6]. Initial antibiotic therapy with glycopeptides is the most rational choice, but therapy should be switched to β-lactams if results of in vitro testing reveal a sensitive organism.

Acknowledgment

We are indebted to Mrs Freund for assistance in the preparation of the manuscript.

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