Bacteremia Secondary to Uncommon Gram-Negative Bacilli Transmitted From the Canine in a Patient With Multiple Myeloma

Abstract

Sphingobacterium multivorum is a gram-negative rod found in the environment and rarely associated with human infections. Sphingobacterium is the causative agent of infections in an immunocompromised host in most cases. We report a rare case of cellulitis in an immunocompromised host by Sphingobacterium multivorum.

Introduction

Sphingobacterium as a genus consists of many different subspecies, which are Sphingobacterium multivorum, Sphingobacterium mizutae, Sphingobacterium spiritorum, and Sphingobacterium thalphphilum. S multivorum is usually found in nature, specifically in soil, plants, water, and food.¹ However, Sphingobacterium also makes up the gut microbiota in domestic canines as they produce sphingophospholipids, regulating homeostasis in their digestive system.² Sphingobacterium is detected in both hospitals and natural environments, and approximately up to 50 species have been identified in this genus.³ A search of the literature reveals only a handful of cases of Sphingobacterium causing infection in an immunocompetent host; most of the cases are seen in individuals who are immunocompromised. Improved microbiological techniques are being frequently used to identify the uncommon organisms causing infections.⁴ The cases usually reported with cellulitis progress to bacteremia and, eventually, sepsis. Our patient presented similarly and was treated promptly, which prevented severe complications.

Case Report

A 70-year-old female presented from her primary care’s office with pain in her legs along with redness and edema. She stated that she had mild bilateral leg swelling for the past 2 weeks. She started having left leg pain and erythema, which was worse on the day of her presentation. The patient admitted that the rash started after her dog played with her legs, playfully scratching, biting, and licking her leg intermittently. She denied any fever, chest pain, abdominal pain, or confusion. Her past medical history was significant for multiple myeloma, which was in remission at the time of presentation on maintenance therapy with lenalidomide and dexamethasone. Other past medical history was significant for chronic back pain secondary to spinal stenosis, and osteolytic lesions from multiple myeloma, chronic obstructive pulmonary disease, hypertension, hypothyroidism, and hyperlipidemia. Medications on admission include oxycodone extended-release 40 mg twice daily, oxycodone immediate-release 10 mg every 4 hours as needed, lisinopril 10 mg daily, amlodipine 10 mg daily, levothyroxine 75 µg daily, dexamethasone 12 mg once weekly, lenalidomide 10 mg daily for 3 weeks on and 1 week off, aspirin 81 mg daily, and atorvastatin 10 mg at night time.

Laboratory analysis on admission is summarized in Table 1. A bedside ultrasound was negative for deep venous thrombosis. The patient was admitted with an initial diagnosis of cellulitis and pneumonia and seen by infectious disease. Procalcitonin on admission was 3.2 ng/mL (0-0.5 ng/mL). Chest X-ray showed focal opacities and infiltrates in the right lung. She was started empirically on cefepime, levofloxacin, and vancomycin for 5 days. Two sets of blood cultures were positive for Sphingobacterium multivorum identified by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry with sensitivities, as mentioned in Table 2. Given susceptibility to quinolones, vancomycin was stopped, and levofloxacin was continued. Chest computed tomography scan without contrast showed a benign right upper lobe nodule measuring 4 mm.

Table 1.

Admission Laboratory Data.

	Laboratory value	Normal values
Hemoglobin	14.3 g/dL	12-16 g/dL
White cell count	10.8 K/µL	4.5-10.8 K/µL
Platelet count	164 K/µL	130-400 K/µL
Blood urea nitrogen	19 mg/dL	7-8 mg/dL
Serum creatinine	1.07 mg/dL	0.6-1.3 mg/dL
Serum sodium	135 mmol/L	136-145 mmol/L
Serum potassium	4 mmol/L	3.5-5.3 mmol/L
Procalcitonin	3.2 ng/mL	<0.5 ng/mL—low risk for sepsis
		0.5-2.0 ng/mL—indeterminate risk for sepsis; suggest repeat in 6-24 hours
		>2.0 ng/mL—high risk for sepsis
Albumin	3 g/dL	3.4-5 g/dL
Globulin	3.8 g/dL	2.4-3.5 g/dL

Table 2.

Antimicrobial Sensitivities.

Antimicrobial	Interpretation	Value
Ampicillin	Resistant	≥32 µg/mL MIC
Ampicillin/sulbactam	Resistant	≥32 µg/mL MIC
Ceftriaxone	Resistant	16 µg/mL MIC
Ceftazidime	Resistant	≥64 µg/mL MIC
Cefazolin	Resistant	32 µg/mL MIC
Ciprofloxacin	Susceptible	0.5 µg/mL MIC
Gentamicin	Resistant	≥16 µg/mL MIC
Imipenem	Resistant	≥16 µg/mL MIC
Levofloxacin	Susceptible	≤0.12 µg/mL MIC
Trimethoprim-sulfamethoxazole	Susceptible	≤0.12 µg/mL MIC
Tobramycin	Resistant	≥16 µg/mL MIC
Piperacillin/tazobactam	Resistant	≥128 µg/mL MIC

Abbreviation: MIC, minimum inhibitory concentration.

The patient’s cellulitis improved with the antimicrobial regimen, and she was discharged with 7 days of levofloxacin. Repeat blood cultures were negative. During the patient’s admission, oncology was consulted for managing her multiple myeloma, both lenalidomide and dexamethasone were stopped temporarily and resumed after she completed the course of antimicrobials. The remainder of her hospital stay was otherwise uneventful.

Discussion

Sphingobacterium multivorum is an omnipresent non-lactose-fermentative gram-negative bacillus with cell membrane rich in sphingophospholipids, rarely causes infection in humans, and can be life-threatening with resistance to many commonly administered antimicrobials.⁵ Initially, it was classified as Flavibacterium but renamed as Sphingobacterium because of sphingophospholipids-rich cell membrane.¹ It was first described in 1981 as Flavibacterium.⁶ Yabuuchi et al described the genus Sphingobacterium in 1983.⁷ It survives in moist environments and can contaminate laboratory culture and blood culture systems; hence, potential contamination should be considered when multiple cases are reported from the same facility.⁵

Like other cases reported in the medical literature from genus Sphingobacterium, S multivorum is known to cause cellulitis and other pathologies in the immunocompromised host. In the case report, our patient presented with telltale signs of cellulitis, which was different from other cases described in the literature as the source of infection. To date, 2 cases of S multivorum, one causing cellulitis and other causing necrotizing fasciitis, have been described in the literature, with both patients being immunocompromised and on long-term steroids.³

Sphingobacterium multivorum, as discussed earlier, is usually found in the environment, predominantly in the soil and water. However, in our patient, she could have acquired the infection from her pet canine. As this organism lives in the canine’s gut, they can get easily transferred by saliva to a host, and in the immunocompromised host, they can potentially lead to fatal conditions. Several cases have been reported where the immunocompromised host had eventual bacteremia secondary to their primary mode of infection.²

Other infections associated with S multivorum include necrotizing fasciitis, peritonitis, respiratory infection, cystitis, meningitis, bacteremia mostly in immunocompromised patients such as patients with malignancy undergoing chemotherapy, patients with diabetes mellitus, chronic liver disease, patients undergoing hemodialysis, cystic fibrosis patients, patients with HIV (human immunodeficiency virus), and patients with the chronic obstructive pulmonary disease.^1,5

For bacterial identification, the 16S ribosomal RNA sequence is widely used primarily with unreliable results on conventional testing. The taxonomy of genus Sphingobacterium is still being determined since several organisms were identified from the soil, sludge, plants, and food in the past decade.⁸

Sphingobacterium is known to show a varying degree of pattern to antimicrobial resistance. In our case, the microbe was susceptible to trimethoprim-sulfamethoxazole and quinolones but resistant to cephalosporins. This was not surprising given that Sphingobacterium can produce an extended β-lactamase, making it resistant to cephalosporins.⁹ The patient, in our case, made an excellent recovery from the use of trimethoprim-sulfamethoxazole and levofloxacin. However, 2 recent cases discussed by Nemoto et al responded to cefazolin with complete resolution of the symptoms even though the minimum inhibitory concentration of cefazolin against the isolated organisms was >4 µg/mL.³

Conclusion

Infections with Sphingobacterium have been gaining more attention recently, but a literature review shows a limited amount of cases where this microbe is blamed for a series of infections. While a few cases of Sphingobacterium, causing infection in the immunocompetent host, have been documented, most cases show infections in an immunocompromised host. It is also worthwhile to note that sometimes the most innocuous sources of infections can be overlooked. Our case reiterates that in an immunocompromised host, even the most harmless microbe can become an opportunistic pathogen; hence, it is essential that along with a detailed history, appropriate workup can go a long way in the care of our patients.