Lachnoanaerobaculum orale bacteremia in a patient with acute myeloid leukemia and stomatitis: An emerging pathogen

Abstract

Background

Lachnoanaerobaculum orale is a newly described, obligately anaerobic gram-positive bacillus. The first report of invasive disease caused by L. orale was described in a patient with acute lymphocytic leukemia following systematic chemotherapy. Here we describe another case of L. orale bacteremia in a patient with a hematologic malignancy following chemotherapy-induced neutropenia.

Methods

We present a case of a 46-year-old woman with a recent diagnosis of AML who presented to Sunnybrook Health Sciences Center with febrile neutropenia following induction chemotherapy with daunorubicin-cytarabine (3 +7 regimen) with Gemtuzumab and Ozogamycin. Despite being on intravenous pipercillin-tazobactam she remained febrile. Following our clinical assessment and investigations, potential sources of infection included a swollen digit and severe mucositis.

Results

One blood culture from admission grew Lachnoanaerobaculum orale in the anaerobic bottle, identified by Matrix-Assisted Laser Desorption Ionization-Time of Flight (MALDI-TOF). The isolate also underwent whole-genome sequencing using methods that have been described previously. Results demonstrated the organism was susceptible to cefoxitin, clindamycin, meropenem, metronidazole, penicillin, and piperacillin-tazobactam. We concluded that the source of this patient’s bloodstream infection to be chemotherapy-induced stomatitis.

Conclusion

With the increasing use of intensive immunosuppressive regimens and hematopoietic stem cell transplantation for patients with hematologic malignancies, there has been an increase in the incidence and detection of bloodstream infections due to anaerobic organisms. This is only the second case report of L. orale bacteremia, highlighting its emerging role as an opportunistic pathogen in immunocompromised patients.

1. Introduction

Lachnoanaerobaculum orale is an obligately anaerobic, filamentous, gram-positive, spore-forming bacillus [1]. It was first described by Hedberg et. al as part of the commensal flora from the saliva of a healthy man [1]. The first report of invasive disease caused by L. orale was described in February, 2022 in a 69-year-old man with acute lymphocytic leukemia following chemotherapy induced neutropenia and stomatitis [2]. From anaerobic blood cultures, L. orale was isolated.

Here we describe another case of L. orale bacteremia in a patient with a hematologic malignancy following chemotherapy-induced neutropenia.

2. Case presentation

A woman in her 40 s with acute myeloid leukemia (AML) presented to hospital with febrile neutropenia. She had received induction chemotherapy with daunorubicin-cytarabine (3 +7 regimen) with Gemtuzumab and Ozogamycin 12 days before presentation. Her comorbidities included latent tuberculosis and hepatitis B core antibody positivity for which she was on isoniazid and entecavir, respectively.

On initial presentation, she noted fevers at home with skin discoloration of the third digit of her right hand. Initial vital signs were as follows: heart rate 122 beats per minute, blood pressure 144/97 mmHg, 98 % on room air, and temperature of 36.7 degrees Celsius. The third digit of her right hand was swollen at the distal interphalangeal joint with ecchymoses at the distal phalanx extending into the dorsal palm, but without open ulceration. She did not have a central venous catheter. Her hemoglobin was 91, white blood cell count was 0.2, neutrophils of 0, and platelets were less than 3. X-ray of the hand did not show acute fracture but there was mild soft tissue thickening of the third digit. She was admitted to the complex malignant hematology service. She was seen by the plastic surgery service for possible hand cellulitis. She was started on antimicrobial therapy with intravenous piperacillin-tazobactam.

By day 3 of her presentation, she had persistent fevers (39.3 degrees Celsius) despite antibiotics, and so the Infectious Diseases service was consulted. On examination, in addition to her dactylitis, she was noted to have petechiae on her palate, as well as a thick, pink-based papule with a dark gray tinge on the left side of her buccal mucosa. She also had tenderness of the right submental region.

One blood culture from admission grew Lachnoanaerobaculum orale (Fig. 1) in the anaerobic bottle, identified by Matrix-Assisted Laser Desorption Ionization-Time of Flight (MALDI-TOF).

Fig. 1.

L. Orale colonies on Brucella agar with Hemin and Vitamin K (HK) in anaerobic condition.

The isolate underwent whole-genome sequencing using methods that have been described previously [3]. Repeat blood cultures taken after initiation of antimicrobial therapy were negative. CT neck showed no signs of head and neck infection, CT right hand showed an effusion at the third metacarpophalangeal joint in keeping with dactylitis, and CT abdomen and pelvis showed persistent cecal thickening (compared to a scan one month prior), but no acute findings. She did not have an echocardiogram given low suspicion for endovascular infection. On day 6 of her admission, plastic surgery attempted needle aspiration of the distal D3 fingertip, but no purulent drainage was obtained. On day 8 of her hospital admission, the fever resolved and she had neutrophil recovery.

Given the pathogen isolated, and her clinical presentation, the most likely source of the patient’s bacteremia was felt to be chemotherapy-induced stomatitis. Her dactylitis was concluded to be unrelated to her bacteremia. Her baseline uric acid level was normal at 118umol/L (drawn 39 days prior to her admission), however uric acid level was not obtained during this admission. Her antimicrobial therapy was transitioned to oral amoxicillin-clavulanic acid and ciprofloxacin to complete 14 days of therapy in total for febrile neutropenia and bacteremia. Colonoscopy was completed as an outpatient to investigate the cecal thickening, and this was normal to the terminal ileum.

The L. orale isolate was sent to the Public Health Ontario Reference Laboratory (PHOL) for confirmation of identification using MALDI-TOF and antimicrobial susceptibility testing. Results demonstrated the organism was susceptible to cefoxitin, clindamycin, meropenem, metronidazole, penicillin, and piperacillin-tazobactam. We did not obtain quinolone susceptibilities.

3. Discussion

L. orale is member of the Lachnoanaerobaculum genus which also includes L. saburreum, L. umeaense, and L. gingivalis. [1], [2] A Swedish study first reported the isolation of L. umeaense from small bowel biopsy of a patient with celiac disease and L. orale from saliva of a healthy man [1]. Cells of L. orale frequently occur in groups and do not demonstrate hemolysis. Colonies have a diameter of 1.5–3 mm and are circular with rhizoid shape after 3 days. [1].

There is only one other published case report of bloodstream infection due to L. orale, in a man a with new diagnosis of acute lymphocytic leukemia who received chemotherapy with vincristine, daunorubicin, cyclophosphamide, and prednisone and developed stomatitis [2]. Drug susceptibilities using the gradient diffusion strip method demonstrated low minimum inhibitory concentrations (MIC) to most beta-lactams but higher MICs to fluoroquinolones [2]. L. gingivalis, which had been initially described as endemic to dental plaque, has also been recently described as a cause of bacteremia in a neutropenic patient with acute myeloid leukemia [4], [5].

In the last several decades, there has been an increase in the incidence and detection of bloodstream infections due anaerobic organisms [6]. Several factors have likely contributed to this, including more intensive immunosuppressive therapies and expanding use of hematopoietic stem-cell transplantation for hematological malignancies [6]. Additionally, the incidence of stomatitis varies with chemotherapeutic agents used. Agents that affect DNA synthesis, such as methotrexate, cytarabine, and 5-flourouracil, have been reported to have a high incidence of oral mucositis [7]. The adoption of technologically advanced bacterial identification methods, including MALDI-TOF, has also led to increased detection of invasive infections due to either novel organisms or those that were previously difficult to identify or were misclassified [8]. Interestingly, whole genome sequencing (WGS) identified the isolate as L. gingivalis, suggesting members of the Lachnoanaerobaculum genus may not be easily differentiated by MALDI-TOF, and further sequencing of additional species may be helpful.

This is only the second case report of L. orale bacteremia, highlighting its emerging role as an opportunistic pathogen in immunocompromised patients. Synthesis of case reports and further studies will be needed to better define the susceptibility patterns of this organism.

Ethical approval

Not required.

Consent

Written consent was obtained from the patient for publication of this case report.

Authorship Statement

All authors contributed to the preparation of the manuscript.

Author contributions

Conception and design: NS, SH, NA. Analysis and interpretation of the data: NS, SH, FM, PA, RK, NA. Drafting of the article: NS, SH, RK, NA. Critical revision of the article: NS, SH, RK, NA. Final approval of the article: NS, SH, RK, NA.

Declaration of Competing Interest

The authors have no conflicts of interest to declare.