Moraxella lacunata Septic Arthritis in a Patient with Lupus Nephritis

Abstract

Moraxella lacunata is a rare, usually commensal gram-negative rod most commonly associated with eye infections. We report a unique case of noniatrogenic M. lacunata bacteremia and septic knee arthritis in a patient with class III-IV lupus nephritis and speculate on the association between invasive Moraxella infection and renal impairment.

CASE REPORT

On 5 December 2008, a 24-year-old woman with lupus nephritis presented at her routine nephrology appointment with a 1-week history of increasing edema, arthralgia, and intermittent fevers. One week prior, she had been discharged from a referring institution on a prednisone taper for an acute lupus flare. She was taking 60 mg of prednisone per day with 500 mg of mycophenolate mofetil (CellCept; self-initiated) twice per day at the time of her nephrology appointment. Examination revealed severe lower-extremity pitting edema, swollen knees, and a tender, swollen right wrist. Movement of her left knee induced severe pain.

At baseline, the patient's biopsy-proven class III-IV lupus nephritis was associated with mild joint swelling and minimal periorbital edema, typically responsive to corticosteroids and immunosuppressive therapy. Given her recent history of high-dose steroid and immunosuppressant usage, investigation into a source of her worsening renal dysfunction separate from her underlying lupus nephritis was warranted.

Laboratory studies indicated leukocytosis (white blood cell count, 24 × 10³/μl [normal range, 3.6 × 10³ to 11.0 × 10³/μl]) and acute renal failure requiring emergent hemodialysis (potassium level, 6.8 meq/liter [normal range, 3.5 to 5.1 meq/liter]; blood urea nitrogen level, 200 mg/dl [normal range, 7 to 25 mg/dl]; and creatinine level, 4.2 mg/dl [normal range, 0.7 to 1.6 mg/dl]). Fecal cultures were unrevealing, urine cultures revealed 50,000 to 100,00 CFU/ml of Citrobacter koseri, and two of two blood cultures grew Moraxella lacunata (Table 1). She remained febrile with persistent M. lacunata growth in two of two blood cultures on the second day of admission, despite therapy every 6 h with 2.25 g of intravenous piperacillin-tazobactam, chosen for its broad-spectrum coverage of gram-negative rods including pseudomonas. Further studies to evaluate the source of her persistent bacteremia were performed; an echocardiogram showed a small pericardial effusion with no evidence of endocarditis, and bilateral knee arthrocentesis revealed M. lacunata growth from left knee synovial fluid (Table 2) .

TABLE 1.

Characteristics of the bacterium isolated from the patient's bloodstream

Test	Result
Anaerobic culture	Negative
Aerobic culture	Positive
Gram staining	Gram-negative rods
Cultivation on:
Blood agar	Shiny colonies and dry colonies
MacConkey agar	No growth
Chocolate agar	Shiny, mucoid colonies
Oxidase test	Positive
Indole test	Negative
Catalase test	Positive
Vitek 2a	Moraxella group, 99% confidence
API 20NEb	M. lacunata, 85% confidence

^aVitek 2 (bioMerieux Inc., Durham, NC) is an automated system for bacterial identification and antibiotic susceptibility testing.

^bAPI test kits (bioMerieux Inc., Hazelwood, MO) are used for identification of bacteria and yeast.

TABLE 2.

Positive biochemical reactions with identification cards for gram-negative bacteria^a

Test	Agent yielding positive reaction
Vitek 2 card	Glutamyl arylamidase p-nitroanilide (AGLTp)
	Lipase (LIP)
	Tyrosine arylamidase (TyrA)
	Glycine arylamidase (GlyA)
apiweb	Nitrate (NO3)
	Gelatine (GEL)
	Oxidase (OX)

^aThe patient's blood and synovial fluid isolates were identified based upon the following characteristics: aerobic gram-negative rods grew on sheep blood and chocolate agars but not MacConkey agar, were oxidase and catalase positive, and were indole negative (Table 1). When the isolates were tested with the Vitek 2 instrument (bioMerieux Inc., Durham, NC) using identification cards for gram-negative bacteria, an identified of M. lacunata was obtained with 99% confidence. When the isolates were tested using a manual API 20NE strip (bioMerieux Inc., Hazelwood, MO), the same identification was obtained with 85% confidence (Table 1).

Following septic knee debridement, she clinically improved with 10 days of intravenous piperacillin-tazobactam and progressive advancement in her activities of daily living. She remained afebrile until discharge. Surveillance blood and synovial fluid cultures on the third day of admission revealed no further bacterial growth. She continued to improve with eventual resolution of her renal failure.

This case highlights the invasive potential of M. lacunata and emphasizes the importance of searching for occult sources of infection, particularly in an immunocompromised host with renal failure.

M. lacunata is a gram-negative rod of usually low virulence that has most commonly been associated with eye infections and, occasionally, upper respiratory tract infections. We report a case of noniatrogenic M. lacunata bacteremia and septic knee arthritis in a patient with biopsy-proven WHO class III-IV lupus nephritis. Although there have been prior cases of septic arthritis associated with organisms of the Moraxella genus, this is the second case of invasive M. lacunata infection secondary to septic arthritis to be reported worldwide. The first reported case of septic arthritis associated with M. lacunata occurred in a 78-year-old man with human immunodeficiency virus infection (11).

A review of prior reports suggests a possible association between Moraxella infection and renally compromised hosts; at the time of infection, one patient was undergoing hemodialysis (2), another had nephrotic syndrome (3), and another had diabetic nephropathy (8). Similarly, our patient had lupus nephritis requiring hemodialysis when she was diagnosed with M. lacunata septic arthritis. Chronic renal failure and hemodialysis impair the normal response of the immune system through several mechanisms: by impairing granulocyte locomotion, phagocytosis, and intracellular killing; by depressing cell-mediated immunity; and by activating the alternate complement pathway during hemodialysis (1, 7, 9).

In addition to renal compromise, other comorbidities associated with M. lacunata invasive infection include steroid use, preexisting infection with human immunodeficiency virus, and the presence of prosthetic valves (1, 8). However, there have been reports of M. lacunata endocarditis in immunocompetent hosts with native heart valves as well, suggesting that, independent of the immune status of the host, M. lacunata may be a more invasive pathogen than previously recognized (4, 5, 6).

Further, it appears that Moraxella species may have a predilection for bone and joint involvement. Moraxella species including Kingella kingae (previously known as M. kingii) and M. osloensis have been isolated from nonimmunocompromised patients and children with osteoarticular infections (2, 10, 13). Prior studies with respiratory tissues have shown M. catarrhalis invasion to be dependent on a trigger-like uptake mechanism involving macropinocytosis, leading to lamellipodium formation and engulfment of the invading organism into macropinosomes (12). However, it is unclear at this time whether a similar mechanism may be involved in Moraxella's propensity for bone and joint invasion.

While the roles of the immune status of the host and the presence of renal failure in facilitating invasion necessitate further study, the case reported herein and the literature review suggest that M. lacunata, traditionally viewed as an ophthalmic and respiratory tract pathogen, should not be overlooked in its potential for bone, joint, and endocardial invasion.