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Human Infections Due to Streptococcus acidominimus

Dalal, Aman MD*; Urban, Carl PhD*†

Infectious Diseases in Clinical Practice: September 2008 - Volume 16 - Issue 5 - p 283-284
doi: 10.1097/IPC.0b013e31816fd608
Review Articles

Streptococcus acidominimus, a gram-positive coccus of the viridans streptococci group, was first isolated in 1922 from bovine sources and is usually associated with metritis in cattle. On rare occasions, it has been associated with infections in humans. We report 2 cases of human infections due to S. acidominimus.

*Division of Infectious Diseases, New York Hospital Queens, Flushing, NY; and †Department of Microbiology, Weill Cornell Medical College, New York, NY.

Address correspondence and reprint requests to Aman Dalal, MD, 56-45 Main Street, Flushing, NY 11355. E-mail:

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The patient was an 80-year-old white female brought to the emergency room with complaints of lethargy and fever of 1-day duration. The patient had medical history of diabetes mellitus, hypertension, and coronary artery disease and surgical history of aortic vale replacement about 10 years ago.

On initial examination, patient had a temperature of 39.8 °C and blood pressure of 110/72 mm Hg. Cardiac auscultation revealed a 2/6 systolic murmur in the aortic area. There were no peripheral stigmata of endocarditis including Janeway lesions, Roth spots, or splinter hemorrhages and no history of recent dental or gastrointestinal procedures.

Initial blood analysis showed white blood cell count of 21,700/μL, with 86% neutrophils, C-reactive protein of 15.9 mg/dL, and serum creatinine of 0.8 mg/dL. A chest radiograph did not reveal any infiltrates. Two sets of blood cultures were drawn, and the patient was started on intravenous vancomycin 1 g every 24 hours and piperacillin/tazobactam 4.5 g every 8 hours. Blood cultures were positive for gram-positive cocci in chains in all 4 bottles, which were later identified as Streptococcus acidominimus (API 20 Strep system). Susceptibility by Kirby-Bauer disk-diffusion method revealed S. acidominimus susceptible to penicillin, clindamycin, erythromycin, ceftriaxone, doxycycline, chloramphenicol, levofloxacin, and vancomycin.1

Transthoracic echocardiography revealed normal functioning valves, without evidence of vegetation, thrombi, or pericardial effusion. Transesophageal echocardiography on hospital day 2 detected a small, mobile echodensity attached to the aortic valve, consistent with a vegetation. Subsequent blood cultures remained negative. Urine and sputum cultures remained negative for bacterial growth.

The patient was initially started on vancomycin 1 g every 24hours and piperacillin/tazobactam 4.5 g every 8 hours and subsequently changed to ceftriaxone 1 g every 12 hours and oral rifampin 300 mg every 12 hours. Ceftriaxone was continued for a total of 6 weeks and rifampin for the first 3 weeks. A subsequent transesophageal echocardiography at the completion of antibiotic therapy did not reveal any vegetation, and the patient had a complete recovery.

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The patient was a 76-year-old man, who presented to the emergency room with a 2-day history of productive cough and fever. The patient had a medical history of metastatic non-small cell lung cancer status post last chemotherapy 5 weeks earlier, hypertension, and coronary artery disease.

On initial examination, the patient had a temperature of 38.9°C and blood pressure of 90/62 mm Hg. Cardiac auscultation did not reveal any murmur, and chest auscultation revealed crackles in the right lower lung zone.

The initial blood analysis showed a white blood cell count of 32,700/μL, with 76% neutrophils and 20% bands, C-reactive proteinof 25.1 mg/dL, and serum creatinine of 0.7 mg/dL. A chest radiograph showed a large infiltrate in the right lower lobe. Two sets of blood cultures were drawn, and administration of intravenous vancomycin 1 g every 12 hours and cefepime 2 g every 8 hours was started. Blood cultures were positive for gram-positive cocci in chains in all 4 bottles within 24 hours, which were later identified by the API 20 Strep system as S. acidominimus. The isolate was susceptible to penicillin, clindamycin, erythromycin, ceftriaxone, doxycycline, chloramphenicol, levofloxacin, and vancomycin by the Kirby-Bauer disk-diffusion method.1 Sputum culture also grew S. acidominimus with similar susceptibilities and subsequent blood cultures remained negative.

Administration to the patient of vancomycin 1 g every 12 hours and cefepime 2 g every 8 hours was initially started to cover methicillin-resistant Staphylococcus aureus and resistant gram-negatives because the patient was previously hospitalized 4 weeks earlier with chest pain. The antibiotic regimen was changed to ceftriaxone 1 g every 12 hours once susceptibilities were availableand continued for a total of 4 weeks. The patient had a complete recovery.

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Streptococcus acidominimus, a gram-positive coccus, was first isolated in 1922 from bovine sources and is usually associated with metritis in cattle.2 Streptococcus acidominimus is frequently described in the veterinary literature including its isolation, postmortem, in slaughtered poultry.3-5 The organism has rarely been described as a pathogen in humans.6-9 Previous reports document the normal habitat of S. acidominimus as in the bovine vagina, on the skin of calves and in raw milk.2 It may be found in wounds or abscess and in the genital tract of up to 6% in women.4,10 Vaginal swabs from our patient (case 1) grew Enterococcus faecalis. We were unable identify a source of the infection in both of our patients.

As reviewed by Cone et al,9 the genus Streptococcus is classified into 4 groups which include (a) the β-hemolytic streptococci; (b) non-β-hemolytic streptococci, which includes the pneumococci, Streptococcus bovis group, and the viridans streptococci; (c) the nutritionally variant, Abiotrophia and Granulicatella species; and (d) S. acidominimus and other unusual streptococci species.

The clinical as well as epidemiological significance ofthis organism is obscure because of its rare association withinfections in humans and previous lack of speciation inthe clinical microbiology laboratory. A computerized MEDLINE search for review of English-language literature using the terms "Streptococcus acidominimus" and "infection" revealed 4 cases of S. acidominimus infections in humans which are summarized in Table 1. These include 1 case each of endocarditis,7 brain abscess,9 and Gradenigo syndrome which is characterized by ipsilateral paralysis of the abducens nerve, severe pain in the area supplied by the ophthalmic branch of the trigeminal nerve, and an intercurrent inflammatory disease of the inner ear, mastoid sinus, or both. Other principal symptoms are photophobia, excessive lacrimation, fever, and reduced corneal sensitivity.8 A single case documented pneumonia, pericarditis, and meningitis concurrently.6



Streptococcus acidominimus is generally quite sensitiveto β-lactam antibiotics, as were the isolates presented in this report. Because of the paucity of documented case reports, there is no consensus of optimal treatment. Akaike et al6 treated a case of pneumonia, pericarditis, and meningitis with intrathecal gentamicin for 4 days and ampicillin, latamoxef, and minocycline for 4 weeks.6 Brachlow et al7 treated a case of endocarditis due to S. acidominimus initially with cefotaxime, doxycycline, vancomycin, and azithromycin. Cefotaxime was given for 9 days, after which gentamicin was given. Vancomycin and gentamicin were then administered for 6 weeks after discharge.

In summary, S. acidominimus is classified as a member of the viridans group streptococci and is capable of causing serious human infections.6-9 Fortunately, the S. acidominimus isolated in this and in the other reported cases still remains susceptible to ceftriaxone or cefotaxime therapy, and patients treated with these antimicrobial agents alone or in combination with gentamicin or rifampin have had positive microbiological and clinical outcomes. The description of further cases may lead to more formal therapeutic strategies.

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9. Cone LA, Etebar S, Waterbor RB. Brain abscess due to Streptococcus acidominimus: first case report. Surg Neurol. 2007;67(3):296-297.
10. Rabe LK, Winterscheid KK, Hillier SL. Association of viridans group streptococci from pregnant women with bacterial vaginosis and upper genital tract infection. J Clin Microbiol. 1988;26(6):1156-1160.
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