Myroides odoratum Osteomyelitis in a Diabetic Patient: Case Report and Review on a Rare Pathogen

Myroides species constitute a rare cause of human infection and are classified as a gram negative, nonmotile obligate aerobic bacilli that is not thought to be a part of the human microbiome. Previously known as Flavobacterium species, these pathogens have been isolated from environmental sources including water and soil and have rarely been found to cause infection in humans, especially immunocompetent hosts. Myroides odoratum and Myroides odoratimimus were the first and now the most common species isolated and are notably found to be multi-drug resistant organisms. This has led to challenging treatment regimens due to the ubiquitous resistance patterns coupled with the relative unfamiliarity of the pathogen. This case describes a diabetic, but otherwise immunocompetent patient with Myroides odoratum osteomyelitis, being the first reported case of Myroides species osteomyelitis to our knowledge. Discussion is focused on the characteristics of the organism and its known pathogenicity, including typical presentation, resistance patterns, and risk factors for inoculation and subsequent infection.

A 64 year old male with a history of diabetes, hypertension and peripheral vascular disease presented with a one year history of a right great toe wound that had been progressively worsening for one month. Over the past several weeks, the toe wound became red, painful, and swollen and began draining clear fluid. His blood pressure was 100/72 and on exam his right great toe revealed an approximate 6.0 x4.0 cm purulent ulcer along the plantar surface with marked erythematous extension surrounding the entire great toe, most prominent over the hallux. He had a leukocytosis of 20.5, erythrocyte sedimentation rate of 60, and lactic acid was 4.6. X-ray of the right foot revealed osteomyelitis of the hallux of the great toe with associated soft tissue swelling. Blood cultureswere negative for growth. He underwent debridement with intraoperative cultures of the lesion which grew Myroides odoratum with antibiotic susceptibilities depicted in table 1. He underwent right great toe amputation and was started on trimethoprim-sulfamethoxazole in accordance with sensitivity data. He experienced further clinical decline and despite negative blood cultures, developed hemodynamic instability with subsequent multi-organ dysfunction and eventual death. 

Table 1: Antimicrobial Susceptibilities to Myroides odoratum.

Initially discovered 1923, Flavobacterium species have been isolated from ubiquitous environmental settings including soil, fresh and marine waters, seafood products, meat processing plants, and the gut of adult flesh flies [1]. The Myroides genus diverged from Flavobacterium in 1996 due to genomic and phenotypic differences resulting in the two species Myroides odoratum and Myroides odoratimimus. These aerobic, yellow pigmented, non-motile, nonfermenting gram-negative rods produce a characteristic fruity odor, invoking the taxonomic interest in deriving the name Myroides from the Greek word Myron, which means sweet oil or perfume [1,2]. As of 2017 only 48 cases of this rare pathogen have been reported, most prominent in the immunocompromised population including diabetics, cirrhotics, and patients on chronic immunosuppressant therapy [2,3]. 

Given no known association with human microbiologic flora, identification of Myroides species in culture should be treated as a true pathogen. Often cited to cause cellulitis and soft tissue infections, Myroides has also been reported to cause UTI, pneumonia, and bloodstream infection in immunocompromised patients [4]. Upon referencing reported cases of Myroides species from the United States National Institutes of Health’s National Library of Medicine database from 2017, the most common reported manifestation of Myoides infection was UTI with 13 known cases cited by Yagci, et al. as an outbreak in a Turkish hospital, and four additional cases reported by Ktari, et al. [5-7]. The second most commonly reported manifestation was cellulitis totaling eight cases with three of those being from Myroides odoratimus, four being from Myroides odoratum, and one being from Myroides species without specification [2,5,8-13]. Lastly, the third most common manifestation was bacteremia with infected central venous catheter reported by Spanik, et al. totaling fourcases [8]. 

Infection in immunocompetent patients is exceedingly rare, as only one case of Myroides odoratimimus soft tissue infection in a child following a pig bite has been published in the literature. In this case, osteolytic bone lesions were noted at the site of trauma from the pig bite with associated cellulitis, but no underlying osteomyelitis was diagnosed [5]. After further review of the literature, it appears that our case of toe osteomyelitis in this diabetic patient is the first report of Myroides osteomyelitis to date, being confirmed on bone culture. 

The complex and highly variable antimicrobial resistance of this organism results in difficult eradication regardless of infection site, but deep-seated infections such as osteomyelitis suggest additional difficulty in achieving successful treatment. Initial attempts with pharmacologic therapy without debridement or amputation may be limited, as susceptible agents may not be ideal for tissue penetration in such infections and long courses of therapy may result in significant toxicities and side effects. Antibiotic susceptibilities outlined in table 1 display a relative haphazard resistance pattern, with appreciable differences from susceptibilities reported from prior cases in the literature. 

One case of Myroides species UTI reported by Hu, et al. described resistance to ampicillin, amoxicillin, clavulanate, amikacin, aztreonam, chloramphenicol, cephalosporin, imipenem, gentamicin, levofloxacin, meropenem, sulfamethoxazole, tetracycline, ciprofloxacin, and tazobactam tested by antibiotic sensitivity disc testing [14]. 

Another report of 11 strains of Myroides species isolated from UTIs in 11 patients revealed complete resistance with all 11 isolates against ampicillin, piperacillin, cefuroxime, aztreonam, imipenem, and meropenem. Ceftazidime and cefepime each revealed complete resistance with 10/11 isolates and intermediate resistance with 1/11 isolates, and trimethoprim–sulfamethoxazole was fully sensitive in 11/11 isolate [14]. These data suggest relative ubiquitous resistance against beta-lactam’s, namely earlier generation cephalosporins, penicillin derivatives, and Carbapenems with relative preservation of susceptibility to trimethoprim sulfamethoxazole [14]. 

The production of a chromosome-encoded metallo-beta-lactamase has been documented in both M. odoratus and M. odoratiminus, resulting in resistance to beta lactams, monobactams, and carbapenems with variable susceptibility to aminoglycosides, fluoroquinolones, and trimethoprim-sulfamethoxazole [3,5,7]. Mammeri, et al. claims resistance to beta lactams was due to TUS-1 and MUS-1 beta-lactamases [15]. Further antibiotic resistance mechanisms are currently being investigated by whole genome sequencing to further our understanding of these resistance patterns.

There remains much uncertainty in the pathogenesis of Myroides species infection, but it’s consistent trends in antimicrobial resistance patterns and its predilection for immunocompromised hosts shows relative congruence among cases reported to date. Focus of infection also shows consistence among reported cases, with UTI, cellulitis, and blood stream infection being most common, and osteomyelitis being exceedingly rare, with this being the only known reported case to date. Amputation and eventual death of this patient did not allow for strict assessment of treatment success with trimethoprim-sulfamethoxazole in this patient with Myroides osteomyelitis, as further data is still needed to discern optimal treatment in such cases. With our current data, trimethoprim-sulfamethoxazole appears to have the most optimal coverage, especially when compared to beta-lactams. Nonetheless, with multi-drug resistant organisms on the rise, continued anti-microbial stewardship practices coupled with better familiarity of bacteria such as Myroides is paramount in approaching these rare infections.