Lawsonella clevelandensis: an emerging cause of vascular graft infection

Abstract

Lawsonella clevelandensis, an emerging pathogen, was first described in 2016, and has been implicated in abdominal, breast and spinal abscesses in a limited number of cases. Being a fastidious organism, it is primarily identified with molecular methods. With the incorporation of broad-range PCR testing in clinical diagnostics, L. clevelandensis has been increasingly reported in the literature. We describe a case of a 65-year-old man who presented with bilateral psoas abscesses secondary to aorto-bi-iliac vascular graft infection with L. clevelandensis identified using 16S rRNA/PCR sequencing. The patient underwent surgical resection and replacement of infected graft, followed by 6 weeks of intravenous antibiotic therapy and then chronic suppression with doxycycline and cefadroxil. He was infection-free at last follow-up.

Background

Vascular graft infections (VGIs) are associated with significant morbidity and mortality, with an estimated infection incidence of up to 6%.¹ Management of these infections is often times challenging and warrants graft excision and pathogen-directed antimicrobial therapy.

Gram-positive cocci account for at least two-thirds of VGIs, with coagulase-negative staphylococci being the most common causative agent. Intraoperative contamination, haematogenous seeding of the vascular graft during an episode of bacteraemia and spread of infection from contiguous sites such as abdominal/pelvic abscesses are major pathogenic mechanisms for the development of VGI.^{1 2} Diagnosis of VGI is based on clinical, radiological and laboratory findings. Identification of microbiological cause of VGI is critical for optimal management. However, in up to 50% of VGI cases, a causative agent is not established by conventional cultures.^{1 2} With the incorporation of 16S ribosomal (r) RNA gene PCR/sequencing methods in clinical diagnostics,^3–5 a potential pathogen’s nucleic acid may be identified from clinical samples of resected vascular grafts. A previous study demonstrated that a combined approach with culture and 16S rRNA/PCR sequencing performed on resected grafts had higher sensitivity than culture alone to establish a potential pathogen.⁶ 16S rRNA/PCR sequencing may detect non-viable organisms due to antimicrobial therapy prior to extraction and may also help identify non-culturable organisms and redefine the epidemiology of VGI. Lawsonella clevelandensis was first described in 2016 and belongs to a new genus in the Corynebacterineae suborder.⁷ It is a fastidious organism and is primarily identified with molecular methods. Localised abscess formation has been the primary clinical presentation in all cases reported in the literature.^7–11 However, no prior cases of VGI due to L. clevelandensis have been reported.

Case presentation

A 65-year-old retired farmer, with a medical history of infrarenal abdominal aortic aneurysm for which he underwent endovascular aneurysm repair with aorto-bi-iliac graft 2 years prior, presented to our institution with a 1-month history of progressive bilateral inguinal pain.

Associated symptoms included poor appetite, unintentional 30-pound weight loss, night sweats and chills. He denied any fevers. Remaining review of systems, including gastrointestinal, genitourinary, cardiovascular and respiratory, were all negative. Medical history was significant for essential hypertension, hyperlipidemia, coronary artery disease status post-coronary artery bypass grafting and multiple percutaneous coronary interventions, umbilical hernia repair with mesh and L3–S1 laminectomy. On physical examination, he was stable, non-toxic appearing, with a temperature of 37.2°C (oral), blood pressure of 116/72 mm Hg and pulse rate of 99 beats per minute. Cardiovascular and lung examinations were unremarkable, with no murmurs, rubs or gallops identified. No cervical, axillary or inguinal lymphadenopathy was appreciated on examination. There was tenderness along the inguinal ligament, bilaterally. Inspection of the spine revealed a previous surgical site, with no sinus tract, erythema or tenderness identified. Genital examination revealed normal testicular size and no masses. Skin examination did not show any lesions. The remainder of the physical examination was normal. With regard to exposure history, the patient did report of unpasteurised milk ingestion, but denied any raw meat, contaminated food or water ingestion. He had no clinically relevant travel history, tick exposure or tuberculosis contact.

Investigations

Laboratory investigations revealed significantly elevated inflammatory markers, including C reactive protein of 132.8 mg/L (≤8 mg/L), erythrocyte sedimentation rate of 100 mm/h (0–22 mm/h). Complete blood cell count revealed leucocytosis of 17.5×10⁹/L (3.4–9.6×10⁹/L), thrombocytosis 758×10⁹/L (135–317×10⁹/L) and microcytic anaemia with a haemoglobin of 10.8 g/dL (13.2–16.6 g/dL). An ultrasound of the scrotum was obtained with no evidence of orchitis or epididymitis. A CT abdomen/pelvis showed a possible left-sided peri-aortic psoas fluid collection about the previous graft (figure 1, arrow). Out of concern for graft infection, a PET-CT was obtained, which revealed fluorodeoxyglucose avidity within the abdominal aortic aneurysm wall, possible infection within the common iliac portion of the aorto-bi-iliac vascular graft and bilateral psoas abscesses (figure 2). Percutaneous aspiration of the right psoas collection was obtained, and fluid cytology was negative for malignant cells. Bacterial aerobic and anaerobic cultures, mycobacterial cultures, fungal cultures and corresponding stains, as well as broad range PCR, were all negative. The patient then underwent resection of infected Endurant endograft and replacement with cryopreserved aorto-iliac arterial graft, along with drainage and debridement of abscesses. The surgeons noted a large amount of thick yellow-green pus in the aneurysm sac and a friable infected thrombus was also evacuated. Operative samples were sent for histopathological and microbiological evaluation. Abdominal fluid cultures were all negative. Histopathology revealed mild to moderate acute inflammatory infiltrate and a cluster of tiny Gram-variable bacilli that were weakly acid-fast bacilli (figure 3). 16S rRNA/PCR sequencing on aortic aneurysm sac fluid and aortic tissue (4/4 samples) ultimately detected L. clevelandensis. 16S rRNA PCR and sequencing was performed at Mayo Clinic Bacteriology Laboratory on a LightCycler 480II instrument (Roche Diagnostics, Risch-Rotkreuz, Switzerland) to amplify 401 base pairs of the bacterial 16S rRNA gene with SYBR Green detection. The following primers were used: forward, 5′-CGGCCCAGACTCCTACGGGAGGCAGCA-3′; reverse, 5′-GCGTGGACTACCAGGGTATCTAATCC-3′.

Figure 1.

CT abdomen/pelvis at presentation. Left-sided peri-aortic graft fluid collection.

Figure 2.

PET/CT findings at presentation. Bilateral FDG-avid psoas abscesses. Inflammation/infection within the abdominal aortic aneurysm wall and within the common iliac portion of the aorto-bi-iliac vascular graft.

Figure 3.

Histopathological examination of aortic tissue surrounding the infected aortic vascular graft. Fite stain, ×100 magnification demonstrating weakly acid-fast bacilli.

Differential diagnosis

Bilateral inguinal pain and constitutional symptoms in an adult male can be the presentation of a wide range of clinical syndromes, including testicular, abdominopelvic or spinal malignancies, or infections with referred inguinal pain.

Treatment

The patient was initially started on empiric broad-spectrum antibiotic therapy with intravenous vancomycin, cefepime and doxycycline following infected graft resection. Of note, no antibiotic therapy was administered prior to surgical intervention. As the organism did not grow on cultures for antimicrobial susceptibility testing, empiric antimicrobial therapy was chosen based on the literature review. Cefepime was discontinued and patient was treated with a 6-week course of intravenous vancomycin and oral doxycycline, followed by chronic suppression with doxycycline and cefadroxil.

Outcome and follow-up

The patient’s symptoms resolved, and he had an uncomplicated postoperative recovery. At recent 1-year follow-up, the patient had no clinical signs of active infection. Repeat CT and PET-CT imaging shows near complete resolution of infection with minimal fluorodeoxyglucose (FDG) uptake (figures 4 and 5). Considering the patient underwent in situ replacement of an infected graft, he was kept on suppressive oral antibiotic therapy.

Figure 4.

CT at 1-year follow-up. Patent aorto-iliac graft with no findings concerning for infection.

Figure 5.

PET-CT at 1-year follow-up. Interval improvement of the left periaortic metabolic activity consistent with improving infection, with minimal residual FDG activity along the anterior right psoas muscle.

Discussion

L. clevelandensis, an emerging Gram-positive, acid-fast, anaerobic, catalase positive bacterium, has been identified as a causative agent for abscess formation in breast, abdomen and spine.^{9 11–14} Abscess is the common clinical presentation of this organism in all the described cases, with no predisposition of particular anatomical site or underlying disease (table 1). It must be noted that abscesses are frequently polymicrobial and are often mixed with aerobic organisms; however, this was not the case for our patient.

Table 1.

Summary of Lawsonella clevelandensis cases published in the literature

Reference	Age (years), sex	Site of infection	Diagnosis	Anaerobic culture growth	Comorbidities	Antimicrobial therapy	Outcome
Zamora et al 202010	70 Male	Liver abscess	16S rRNA sequence, Kinyoun acid-fast stain positive	Negative	Rheumatoid arthritis, cirrhosis, diverticulosis	Imipenem, moxifloxacin, clarithromycin switched to amoxicillin–clavulanate	Resolution of abscess
Strum et al 201916	70 Female	Inguinal (pre-peritoneal) abscess	Whole genome sequencing, 16S rRNA sequence	Positive; incubation until visible growth	–	Ceftriaxone, metronidazole switched to clindamycin, doxycycline	Resolution of abscess
Goldenberer et al 201912	–	Breast	16S rRNA sequence (partial direct)	Growth after 4–5 days of incubation	–	–	–
Chudy-Onwugaje et al 20198	38 Male	Abdomen RLQ abscess	16S rRNA sequence, acid-fast stain positive	Negative	Refractory ulcerative colitis	Broad spectrum switched to amoxicillin–clavulanate	Resolution of abscess
Favila et al 20189	29 Female	Breast abscess	16S rRNA sequence, Ziehl-Neelsen acid-fast stain positive	Growth after 10 days of incubation	–	Amoxicillin–clavulanate	Resolution of abscess
Kumaria et al 201811	2 Female	Subdural	16S rRNA sequence	Negative	Beckwith-Weidemann syndrome	Cefuroxime and metronidazole switched to amoxicillin–clavulanate	Relapse of abscess after 5 weeks
Navas et al 201613	64 Male	Abdomen LUQ abscess	16S rRNA sequence, Kinyoun acid-fast stain positive	Growth after 6 days of incubation	Pancreatic neuroendocrine tumour	Tigecycline switched to ertapenem and sulfamethoxazole–trimethoprim	Purulent fluid discharge from surgical site
Harrington et al 2013 Case 114	65 Male	Thoracic abscess	16S rRNA sequence	Growth after 13 days of incubation	Metastatic prostate cancer	Ampicillin–sulbactam switched to meropenem, and later to sulfamethoxazole–trimethoprim and finally amoxicillin–clavulanate	Clear yellow non-odorous fluid drainage from surgical site
Case 214	44 Female	Breast abscess	16S rRNA sequence, Kinyoun acid-fast stain positive	Growth after 5 days of incubation	Diabetes mellitus, liver steatosis	Vancomycin switched to cloxacillin, later to amoxicillin–clavulanate	Resolution of abscess
Case 314	23 Female	Breast abscess	16 rRNA sequence, Kinyoun acid-fast stain positive	Growth after 4 days of incubation	Diabetes mellitus, recurrent furunculosis	Ciprofloxacin and metronidazole	Resolution of abscess
Case 414	81 Male	Liver abscess	16 rRNA, Kinyoun acid-fast stain positive	Negative	Coronary artery disease, polymyalgia rheumatica	Broad spectrum switched to clindamycin and sulfamethoxazole–trimethoprim	Resolution of abscess
Present case	65 Male	Abdominal aorto-iliac vascular graft	16S rRNA sequence	Negative	Hypertension, hyperlipidemia, coronary artery disease	Vancomycin, cefepime, doxycycline switched to doxycycline, cefadroxil

Ecologically, L. clevelandensis is abundantly found in the nostrils and oily skin sites such as the alar crease, glabella and occiput.¹⁵ Since intraoperative contamination of a vascular graft is the most common mode of acquisition of infection, it is plausible that the infection developed as a result of contamination of the graft with the patient’s skin flora. However, it has also been proposed that this organism is part of the gut flora, and therefore contiguous infection is also possible.¹²

Due to its fastidious nature, L. clevelandensis may mimic Nocardia spp. and Mycobacterium tuberculosis complex, which could significantly delay correct diagnosis and treatment. Therefore, direct 16S rRNA gene sequencing is the standard method for identification of this organism. Molecular diagnostic methods aid in the identification of such acid-fast positive, culture-negative organisms and also guide the selection of targeted antibiotic therapy, potentially leading to better treatment outcomes.

A recent study found that the sensitivity of molecular methods on extracted vascular grafts was 58%.⁶ However, the sensitivity for aspirate fluid may be lower. We believe this could be attributed to poor aspirate fluid sampling, that is, low volume of aspirate or incorrect tissue sampled.

In our case, the initial 16S rRNA PCR/sequencing on aspirate fluid yielded negative results. Therefore, we believe that negative aspirate fluid can be misleading and it should not be used to rule out infection when clinical presentation and radiological findings are strongly suggestive of infection.

Given the characteristics of L. clevelandensis, we were not able to culture it successfully for in vitro antimicrobial susceptibility testing. However, low minimum inhibitory concentrations to beta-lactams, macrolides, clindamycin and several other antibiotics have been demonstrated and confirmed with whole genome sequencing, though resistance markers may be present.¹² Several authors have been successful to cultivate L. clevelandensis under anaerobic conditions mostly on Columbia sheep-blood agar, using a gas pack in an anaerobe jar, incubating for 4–13 days.9 12–14 16

There are limited data regarding optimal treatment for this organism. Various combinations of amoxicillin–clavulanate, ertapenem, vancomycin, linezolid, metronidazole and sulfamethoxazole–trimethoprim have been used in previously reported cases. The most common antibiotic used have been amoxicillin–clavulanate and sulfamethoxazole–trimethoprim, with a minimum treatment duration of 6 to 8 weeks.7–9 11–14 17 Following American Heart Association guidelines for treatment duration for VGI,¹ our patient completed a 6-week course of intravenous vancomycin and oral doxycycline therapy followed by chronic suppression with doxycycline and cefadroxil. Suppressive therapy was continued at 1-year follow-up as CT and PET-CT (figures 4 and 5) did not show complete resolution of infection. Because of the minimal residual FDG activity and the fact that vascular graft was placed in an infected bed, chronic suppression therapy was prescribed until complete radiographic resolution of infection or as long as the new vascular graft remains in place.

In conclusion, our patient is the first reported case of VGI with L. clevelandensis. Patients with culture-negative VGI benefit from use of broad-range 16S rRNA PCR testing to establish microbiological diagnosis. Molecular methods may increase the diagnostic yield and help with prompt identification of fastidious, non-cultivable and atypical pathogens responsible for VGI.

Learning points.

• Lawsonella clevelandensis is a fastidious pathogen primarily detected using 16S rRNA PCR testing.

• Clinical infections due to this organism present with localised abscess formation.

• Our case highlights the importance of incorporating molecular diagnostic methods in cases of vascular graft infection, where conventional cultures are negative.

• Susceptibility testing can rarely be attained due to the fastidious nature of L. clevelandensis.

• Low minimum inhibitory concentrations to beta-lactams and several other antibiotic classes have been reported.