Myroides odoratum Cellulitis and Bacteremia

A Case Report

Abstract

Several Flavobacterium species, comprising a heterogeneous group of Gram-negative bacilli, have been reclassified as Myroides species. Myroides odoratum, one of the species, has been reported to cause opportunistic infections. However, its pathogenicity is ill-defined, and data are still emerging. Although infections caused by this bacillus are rare, it is notoriously resistant to multiple antibiotics. We report a case of cellulitis by Myroides odoratum that progressed to septic shock because organism was not suspected initially. After identification of the organism, it responded to administration of susceptible antibiotics. We also reviewed medical literature on this organism.

Myroides odoratum, previously known as Flavobacterium odoratum, is a Gram-negative bacterium. It has been isolated from human urine, feces, wound discharge, sputum, and blood, but its pathogenicity is not well defined, and clinical infections caused by this organism are rare. We report a case of bacteremia and cellulitis due to M. odoratum.

CASE

A 62-year-old man with diabetes mellitus complicated by peripheral vascular disease presented with shortness of breath, general malaise, anorexia, and low-grade fever for 3 to 4 days before admission. On admission, he appeared ill and in mild respiratory distress. He was hypotensive with blood pressure of 88/60 mm of Hg; other vitals were stable. His physical examination revealed mild right lower extremity edema and a superficial, warm, and tender ulcer at the distal anterolateral aspect of the right leg with purulent drainage and surrounding erythema (Fig. 1). Noted as well was a deep ulcer of about 1 cm in diameter with indurated margins on the plantar surface at the first metatarsal bone, draining foul-smelling discharge. The laboratory data were significant only for white cell count of 11 × 10⁹/L with 80% neutrophils and 19% bands. Right foot x-ray revealed no evidence of osteomyelitis. The patient was started empirically on ceftazidime and gentamicin awaiting further cultures. Right foot ulcer was debrided.

FIGURE 1: Ulcer at the anterolateral aspect of the right leg with purulent drainage.

Over the next 24 hours, the patient became lethargic, tachycardiac, tachypneic, and continue to be hypotensive. He was spiking high fever up to 103°F. His cellulitis spread to involve entire anterior aspect of his right shin. Laboratory studies showed worsening renal function, prolonged coagulation profile; and drop in platelet count. Right foot wound culture grew Morganella morgani sensitive to most antibiotics including ceftazidime and gentamicin. All blood cultures grew Gram-negative rods. The same antibiotic regimen was continued, but the patient remains quite ill. Final identification of Gram-negative rods came to be M. odoratum. Antibiotic regimen was then changed to trimethoprim-sulfamethaxazole and ciprofloxacin pending the sensitivity results. Within 24 hours, signs of improvement were noted. The patient became afebrile and hemodynamically stable, with gradual resolution of his cellulitis. M. odoratum was multidrug-resistant and susceptible only to trimethoprim-sulfamethaxazole and quinolones based on minimal inhibitory concentration as shown below.

Ampicillin (16 μg/mL), ampicillin/sulbactam (16 μg/mL), piperacillin (64 μg/mL), piperacillin/tazobactam (64 μg/mL), amikacin (>64 μg/mL), cefazolin (>32 μg/mL), cefotetan (64 μg/mL), cefotaxime (32 μg/mL), ceftazidime (>32 μg/mL), cefepime (16 μg/mL), gentamicin (8 μg/mL), tobramycin (8 μg/mL), amikacin (20 μg/mL), ciprofloxacin (1 μg/mL), levofloxacin (<0.5 μg/mL), trimethoprim/sulfamehoxazole (20 μg/mL), and imipenem (>16 μg/mL).

DISCUSSION

M. odoratum belongs to family Myroides. It was previously known as F. odoratum and placed under genus Flavobacterium. It produces a yellow pigment and fruity odor when grown on MacConkey agar, hence got its name F. odoratum. However, since 1923 when genus Flavobacterium was created, this genus has undergone substantial changes, especially for strains belonging to odoratum species. Recently, Ribotyping and DNA hybridization techniques led to creation of new genus Myroides.¹ Two species have been identified, that is, M. odoratum and Myroides odoratimimus.²

Myroides species are aerobic, nonmotile, oxidase-positive, yellow-pigmented, and nonfermentative or slowly fermentative Gram-negative bacilli that grow at room temperature and 37°C. The strains of M. odoratum are susceptible to desferrioxime in contrast to strains of M. odoratimimus.

Myroides species are commonly inhabitants of soil and water and are not normal components of human microflora. They behave like low-grade opportunistic pathogens. They can cause cellulitis,^3,4 necrotizing fascitis,⁵ urinary tract infection,⁶ surgical wound infection,⁷ ventriculitis,⁸ and endocarditis.⁹ Nosocomial outbreaks have also been reported.⁶

Resistance to multiple antibiotics is characteristic of these species. Myroides species produce a chromosomally mediated noninducible metallo-β-lactamase that is capable of hydrolyzing penicillins, cephalosporins, cephamycins, aztreonom, imipenem, and meropenam.^10,11 In vitro susceptibility varies for fluoroquinolones, but clinical cure has been reported with ciprofloxacin.¹² They are also susceptible to trimethoprim-sulfamethoxazole.¹²

Resistance of M. odoratum to ceftazidime and gentamicin was responsible for lack of improvement of our patient's condition. He only improved when ciprofloxacin and trimethoprim-sulfamethaxazole were started. Such dramatic improvement has been seen in other reported cases of skin and soft tissue infections complicated by Myroides bacteremia.^3-5

Skin appears to be the most likely portal of entry. Ability of this organism to invade the blood stream, as reported by others, illustrates its invasive potential.^3-5,9 Therefore, M. odoratum should be part of the differential diagnosis of skin and soft tissue infections especially when complicated by Gram-negative bacteremia and/or when patient is not responding to traditional β-lactam antibiotics.