Epidural Abscess Caused by Streptobacillus moniliformis

Abstract

bWe present an interesting case of a patient who developed an epidural abscess caused by Streptobacillus moniliformis. This is the first report in the medical literature of a spinal epidural abscess associated with this organism. Diagnosis of S. moniliformis infection requires a high degree of suspicion, and a delay may be inevitable when a relevant clinical history is lacking. CASE REPORT We present an interesting case from New Zealand of a patient who developed an epidural abscess caused by Streptobacillus moniliformis on a background of previous spinal surgery.The patient, a 58-year-old male, presented with a 2-week history of right-sided flank pain, fevers, and lower limb weakness to the extent that he was unable to walk. He had a decreased sensation of bladder filling.He had undergone spinal laminectomy for an L4/L5 radiculopathy 6 months prior to presentation. Other past medical history included hypertension, hypercholesterolemia, and gout. A month before his admission, the patient recalled sustaining a minor abrasion on the back of his hand, which was licked on several occasions by his dog. No history of contact with rats was elicited from the admission history. On examination, he was febrile. There was marked weakness of muscles innervated by L5 and S1 on both sides. Anal tone was absent.Urgent magnetic resonance image (MRI) scanning demonstrated the presence of a large epidural abscess anterior to the L4, L5, and S1 vertebrae, compressing the thecal sac. There was also evidence of osteomyelitic involvement of these vertebrae along with septic arthritis of the facet joints between L2 and S1 ( Fig. 1).The patient was placed on empirical intravenous (i.v.) flucloxacillin, and urgent surgical drainage of the epidural abscess was performed. The abscess fluid was culture negative for bacteria after 10 days of incubation on sheep blood agar, chocolate agar (CO 2 incubation at 37°C), and fastidious anaerobic agar (anaerobic incubation at 37°C). An aliquot of the fluid was added to an aerobic blood culture bottle (BD Bactec FX) and was negative after 10 days of incubation. The aerobic bottle from a blood culture set (BD Bactec FX, paired aerobic and anaerobic bottles) taken on admission was positive after 2 days, with slender, Gram-negative bacilli seen on the Gram stain. The blood culture was subcultured onto sheep blood agar, chocolate agar (CO 2 incubation at 37°C), and fastidious anaerobic agar (anaerobic incubation at 37°C). Pinpoint, cream-colored colonies grew on the blood agar and fastidious anaerobic agar after a further 3 days of incubation, and the possibility of a Capnocytophaga species was suggested, which was also consistent with the close contact with dogs in the patient history. At that stage, there were no characteristic features in the Gram stain suggestive of S. moniliformis, such as pleomorphism or a bulbous center. The organism was oxidase negative and catalase negative. Further biochemical identification was not possible, largely because of its fastidious growth requirements.The patient was...

A spinal epidural abscess due to Streptobacillus moniliformis infection following a rat bite: case report

“…Other antibiotics such as cephalosporins, tetracyclines, and aminoglycosides have also been reported to be effective in rat bite fever. 2,8,19 The S. moniliformis isolate from our patient was fully susceptible to all tested antibiotics except for erythromycin and co-trimoxazole.…”

“…While this zoonotic pathogen is generally regarded as a rare cause of infection, the true incidence of S. moniliformis infections is not known because of the difficulties in culturing the bacterium, the nonspecific symptoms of the disease, and uncertainties regarding rat exposure and the route of infection. 2,3,15 In cases of proven rat bite, the risk of infection is estimated to be approximately 10%. 8 Over the past decades, cases of rat bite fever have been mostly associated with exposure to wild rat populations.…”

“…Furthermore, pet store workers and laboratory technicians are at risk for S. moniliformis infections if the animals are not specifically pathogen free. 2,8 The patient in the featured case reported that he had cared for his girlfriend's pet rat and was bitten 6 weeks before the onset of his symptoms. It is remarkable that the spinal epidural abscess (and the respective neurological complications) developed in the absence of the classic symptoms and signs of rat bite fever.…”

“…Most of the standard aerobic blood culture systems contain concentrations of sodium polyanethol sulfonate as an anticoagulant that inhibits the growth of S. moniliformis and can result in a falsely negative blood culture. 2,8 In the case of positive cultures, the examiner must be aware of the variable microscopic appearance and colony morphology. The gram-negative rods are often arranged in long tangled chains and filaments with bulbar swellings.…”

“…19 S. moniliformis infections of the human spine can occur in the form of an epidural abscess, spondylodiscitis, or a psoas abscess and have only rarely been reported. 2,7 We present what we believe is the first case of an epidural abscess caused by S. moniliformis located in the thoracic spine.…”