Monica Bustos, MSHS, SM(ASCP)CM

A 74-year-old man with a history of atrial fibrillation, chronic renal impairment, diabetes mellitus II, essential hypertension, gout, and hyperlipidemia presented to the emergency room with hypotension, some shortness of breath, and dizziness. The patient had a sudden onset of shortness of breath with acute decompensation and hypotension the morning of presenting. Vital signs showed a temperature of 98.2oF, blood pressure of 157/89, and pulse ox of 94% on room air with an observation of being weak with trouble ambulating. The patient was also found to be in atrial fibrillation with rapid ventricular response, with a heartrate above 170 beats per minute at presentation. The patient was started on a diltiazem drip for the atrial fibrillation followed by amiodarone and digoxin was started for hypotension. Intravenous (IV) fluids were pushed due to leukocytosis and lactic acidosis. 

Once the heartrate had improved, the patient was started on IV Piperacillin/Tazobactam for pneumonia and admitted as an inpatient for observation. The pneumonia responded successfully to the antibiotics by the second day. The patient was then weaned from oxygen with no further incidence of acute respiratory failure. The anaerobic bottle of the one set of blood cultures (TREK Diagnostic Systems, Cleveland, OH) drawn in the emergency room became positive with gram-negative spirillum at 27.5 hours of incubation. Broth was subcultured onto Trypticase soy agar with 5% sheep blood, MacConkey, chocolate, and Campylobacter blood agar plates (BBL prepared plated media; Becton, Dickinson Inc., Franklin Lakes, NJ). Repeat blood cultures were collected after the initial collection was reported as positive for bacterial growth, but antibiotics had already been consistently administered for over 24 hours. Patient was discharged after 4 days of IV therapy with no hypoxia at room air. The antibiotics were changed at time of discharge to levofloxacin for 11 days to complete a two-week antibiotic therapy. Follow up care was to be given by the primary provider the following week. Laboratory results at the time of patient discharge were a white blood cell (WBC) count of 7.5 x 103/μl, hemoglobin of 11.2 g/dl, hematocrit of 32.8 g/dl, and a platelet count of 115,000 x103/μL.

The blood agar plates were incubated anaerobically yielded small, translucent, spreading, nonhemolytic colonies that were oxidase and catalase negative at 72 hours. The organism could not be identified biochemically (bioMérieux Inc., Durham, NC). Consequently, the organism was send out to a Mayo Clinic reference laboratory (Rochester, Minnesota) for further testing. The Mayo Clinic identified the organism as Anaerobiospirillum succiniciproducens by matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) using the FDA-approved Vitek MS version MS-CE CLI 2.0.0 on intact cells without extraction (bioMérieux Inc., Durham, NC). Although the species did not have identification by MALDI-tof validated, the confidence value was 99.9%. The identification was confirmed by 16S rRNA gene sequencing performed at the Mayo Clinic. The patient was switched from levofloxacin to Augmentin and due to the continual decline in health after hospital discharge and proper organism identification, was admitted into a rehabilitation facility for continued antibiotic therapy. After two weeks of appropriate therapy, the patient noted full recovery and was sent home.


Anaerobiospirillum succiniciproducens is an anaerobic, gram-negative spirillium that has been isolated from the stool of household pets, such as dogs and cats, as well as humans.3 Previous studies have linked A. succiniciproducens bacteremia to infections with an origin in the host’s gastrointestinal tract.5 In recent decades, A. succiniciproducens has been identified as a rare causative agent of diarrheal illness and bacteremia in humans.7 All reported cases of septicemia and diarrheal illness had a host with a clinical history of underlying immunocompromising conditions, such as diabetes mellitus, heart conditions, cancer, or AIDS.2 

The disease progression of A. succiniciproducens in an immunocompromised host as well as the successful treatment is not well understood in the medical community. Most hypotheses state that A. succiniciproducens is significantly underreported due to similarities with Campylobacter spp., despite both organisms having different growth requirements. Having 56 documented cases from the United States, Europe, Asia, and Africa suggests this organism has a global distribution. All reported cases have occurred in immunocompromised patients with conditions such as diabetes mellitus, cancer, atherosclerosis, and liver disease.4 The global distribution, the zoonotic nature and its propensity to cause infection in immunocompromised hosts as well as the fact that it is difficult to biochemically identify contribute to the likelihood that this organism goes undetected in the clinical laboratory. Most resources also indicate that the 31% mortality rate2 is a high number especially considering the vast clinical improvements in the microbiology and diagnostic fields. The standard treatment profile for A. succiniciproducens remains inconclusive, with documented cases of mortality even though the treatment used showed in vitro susceptibility.4 Some patients have even been documented as recovering without any specific medical intervention.1 

Most studies indicate the gastrointestinal tract as being the most likely portal of entry for cases that progress to bacteremia. However, in this presentation the patient had no history of gastrointestinal discomfort or diarrhea. Large animal farming produces a wide spectrum of respiratory disease due to the complex diversity of inhalants. A. succiniciproducens is frequently utilized commercially during feed-control development for succinic acid production6; this making the organism an occupational risk factor that is likely under-identified. This study suggests that the advanced immunocompromised state of the patient along with the aerosolized feed, produced bacterial pneumonia which turned to bacteremia. During the epidemiology follow-up performed by the Scottsbluff County Public Health Department (Scottsbluff, Nebraska), cattle feed utilizing A. succiniciproducens as the primary fermenter was found. However, due to the complexity of testing required, genome sequencing was unable to be performed.


  1. Tee W, Korman TM, Waters MJ, et al. Three cases of Anaerobiospirillum succiniciproducens bacteremia confirmed by 16S rRNA gene sequencing. J Clin Microbiol 1998;36:1209–1213. 
  2. Kelesidis, Theodoros. Bloodstream Infection with Anaerobiospirillum Succiniciproducens: A Potentially Lethal Infection. Southern Medical Journal104.3 (2011): 205-14. Web.
  3. Malnick H, Williams K, Phil-Ebosie J, et al. Description of a medium for isolating Anaerobiospirillum spp., a possible cause of zoonotic disease, from diarrheal feces and blood of humans and use of the medium in a survey of human, canine, and feline feces. J Clin Microbiol 1990;28:1380–1384. 
  4. McNeil MM, Martone WJ, Dowell VR Jr. Bacteremia with Anaerobiospirillum succiniciproducens. Rev Infect Dis1987;9:737–742. 
  5. Malnick, H. (1997). Anaerobiospirillum thomasii sp. nov., an anaerobic spiral bacterium isolated from the feces of cats and dogs and from diarrheal feces of humans, and emendation of the genus Anaerobiospirillum. Int J Syst Bacteriol 47, 381–384.
  6. Bretz, K., & Kabasci, S. (2011, December 12). Feed-control development for succinic acid production with Anaerobiospirillum succiniciproducens. Biotechnology and Bioengineering, 109(5), 1187-1192. doi:10.1002/bit.24387
  7. Papasian C J, Kragel P J, Enna-Kifer S, Kemmis R, Webb K. Anaerobiospirillum succiniciproducenssepsis. Clin Microbiol Newsl. 1995;17:14–15.