Staphylococcus schleiferi: An Uncommon Pathogen in an Immunocompetent Adolescent with Chronic Osteomyelitis

Staphylococcus schleiferi represents an uncommon pathogen in human infections. As a veterinary pathogen, S. schleiferi causes canine ear and skin infections. Chronic osteomyelitis is a progressive process characterized by bone destruction and the formation of sequestrum. It may be a sequela of untreated or undertreated acute osteomyelitis or septic arthritis. Descriptions detailing the pathogenicity and virulence of S. schleiferi osteomyelitis were limited to a few case reports. Among the three reported cases of S. schleiferi osteomyelitis, immunosuppression, malignancy, and recent surgical procedures were comorbidities. Compared to those who are immunosuppressed, immunocompetent individuals are generally not susceptible to uncommon microorganisms. Early detection of osteomyelitis, aggressive appropriate prolonged antimicrobial treatment and a multidisciplinary approach contribute to optimal recovery. We report the first case of S. schleiferi chronic osteomyelitis in an immunocompetent adolescent.


Introduction
Unlike Staphylococcus aureus, Staphylococcus schleiferi represents an uncommon causative pathogen of osteomyelitis.Osteomyelitis is typically classifed as either acute or chronic depending on the duration of symptoms.Chronic osteomyelitis is a progressive process involving the formation of an abscess, vascularized necrotic bone and the development of a sinus tract [1].Although S. schleiferi difers from S. aureus in many microbiological ways, its identifcation should not be considered a contaminant [2].Of the two known distinct subspecies described, coagulase-negative S. schleiferi subsp.schleiferi accounts for most of the infections in humans as opposed to coagulase-positive S. schleiferi subsp.coagulans [3].Routine microbiology diagnostic protocols may misidentify S. schleiferi as S. aureus due to their similarity.A few case reports in humans illustrate the pathogenicity and virulence of S. schleiferi [4].Exposure to infected dogs as a source of infection was in the majority of those reports [4].Treatment strategies for S. schleiferi osteomyelitis should include aggressive drainage of abscesses, debridement of necrotic bone, and the use of appropriate antibiotic therapy based on bone cultures similar to the guidelines for S. aureus osteomyelitis [1].With a multidisciplinary approach and prolonged antibiotic therapy, optimal recovery can be expected.Nevertheless, it is prudent to monitor S. schleiferi as an emerging zoonotic pathogen, to observe for antimicrobial resistance and to track the potential of nosocomial acquisition and transmission.We describe herein such a case of S. schleiferi chronic osteomyelitis in an otherwise healthy adolescent.

Case
A previously healthy 16-year-old male was admitted for management of a left lower tibia recurrent draining sinus.He sustained injury to the medial aspect of his left lower extremity after jumping of a four-foot wall in an urban construction site located in his native country of Jamaica one year prior to admission.Within a few days of his injury, he was admitted to a local hospital for swelling of the left ankle, an open wound, and fever.He underwent a surgical procedure and received three weeks of antibiotic treatment for reported left tibia fracture and infection.One week after hospital discharge, he immigrated to the United States.Four months after his arrival, he consulted his primary care physician because of a purulent draining sinus.He was prescribed trimethoprim-sulfamethoxazole (TPX-SMX) 160-800 mg twice a day for ten days to treat S. aureus.Another course of the same antibiotic was prescribed when drainage recurred pending surgical consultation.His household included two younger siblings and four domesticated dogs.At admission, there was a small draining sinus anteriorly in the distal third of his left lower extremity without erythema or swelling.He was afebrile.Laboratory fndings included a leukocyte count of 4.

Hospital Course
Surgical intervention included excision of the sinus tract, debridement of necrotic bone, and placement of antibiotic impregnated beads.Bone cultures were positive for S. schleiferi subsp.coagulans resistant to penicillin.He was treated with vancomycin (60 mg/kg/day intravenously divided every 8 hours) for two weeks before transitioning to oral clindamycin (300 mg every 6 hours) based on the susceptibility pattern for a total of six weeks.CRP of <1.0 mg/L and ESR of 4 mm/hr were both normal three months postoperatively.He continued to be asymptomatic at one-year follow up.

Discussion
S. schleiferi represents an uncommon pathogen in human infections [4].In veterinary medicine, the microorganism causes skin and ear infections in dogs [5].Two subspecies of S. schleiferi have been described: subsp.schleiferi by Freney et al. in 1988 [6] and subsp.coagulans by Igimi et al. in 1990 [7].Of the two subspecies, S. schleiferi subsp.schleiferi is more commonly associated with human infections, specifically of wounds, surgical sites, osteomyelitis, and bacteremia [4,8].In clinical settings, subspecies identifcation is  2 Case Reports in Infectious Diseases Case Reports in Infectious Diseases typically not performed since treatment depends on antibiograms and the location of the infection.Due to similarities to S. aureus, reports suggested possible underrecognized, underestimated, and underreported incidence of S. schleiferi [9].Methicillin-resistant S. schleiferi and nosocomial acquisition have been reported [10].Except for a few sporadic case reports, little is known of pathogenicity and virulence [11].To date, three case reports of S. schleiferi osteomyelitis have been found in the literature, Table 1.Immunosuppression, malignancy, and recent surgical procedures were comorbidities in those cases [4].We are reporting the frst case of S. schleiferi chronic osteomyelitis in an otherwise healthy adolescent.Acute osteomyelitis typically presents with symptoms within two weeks of bone injury, whereas chronic osteomyelitis represents a progressive condition, occurring over weeks, leading to the development of necrotic bone or sequestra.Symptoms specifc to chronic osteomyelitis include draining or persistent sinus tracts, poor wound healing, and absent constitutional symptoms.Besides using duration of symptoms, and histopathological fndings to classify osteomyelitis, the Cierny-Mader classifcation is often applied to adults with chronic osteomyelitis.Tis classifcation incorporates the anatomical type and physiological class [12].Our case would be classifed as IIIA when using Cierny-Mader classifcation, III to indicate a localized lesion with medullary and cortical involvement and A for host with a good immune system.
In chronic osteomyelitis, the abscess that forms as a result of infammation and infection leads to the development of vascularized necrotic bone known as sequestrum and potentially, a sinus tract [12].Te prognosis and outcome of chronic osteomyelitis depend on early recognition of symptoms, rapid diagnosis, drainage of abscesses, debridement of necrotic bone, prolonged antimicrobial treatment, and a multidisciplinary approach.A history of trauma, open fracture, surgical trauma, chronic open wound, and an immunocompromised host are predisposing factors of chronic osteomyelitis [12].Supporting laboratory tests to diagnose osteomyelitis such as leukocytosis, elevated ESR, and elevated CRP lack specifcity and are not diagnostic.However, serial CRP levels may be helpful in monitoring clinical response and treatment [13].Imaging studies including the plain radiograph and MRI confrm the clinical diagnosis.Te plain radiograph can identify fracture, periosteal elevation, and hardware in addition to sequestrum and involucrum in advanced cases.MRI, the imaging study of choice, has the highest sensitivity and specifcity in detecting osteomyelitis [14].Fluorodeoxyglucose positron emission tomography (FDG-PET) is the most accurate in diagnosing chronic osteomyelitis and limited by its cost and availability [14].Management of chronic osteomyelitis includes surgical drainage, debridement, and sequestrectomy followed by prolonged aggressive antibiotic therapy.Te bone culture and histopathologic examination will positively confrm the diagnosis of chronic osteomyelitis [12].Special culture techniques may be necessary to identify some organisms.Te sensitivity pattern can guide antibiotic therapy.A multidisciplinary approach has improved prognosis and outcome of chronic osteomyelitis [12].
Our patient developed swelling, an open wound, and fever within days after the fall suggestive of acute osteomyelitis.By history, he underwent a surgical procedure and three weeks of antibiotic treatment.Te recurrent draining sinus over a course of several months and having necrotic bone were consistent with chronic osteomyelitis.Te pathogen entered most likely through the original open wound and not nosocomially acquired in the absence of any hardware.
Te goal of treatment of chronic osteomyelitis aims to eliminate the pathogen and to debride necrotic bone [12].Although the initial empiric antibiotic therapy often begins after obtaining appropriate cultures, the ultimate choice of antibiotic therapy relies on the bone culture and sensitivity pattern [1].Our patient received two courses of TMP-SMX prior to surgical debridement and contributed to the controversy of the optimal route and duration of antibiotic therapy.In a small sample of twenty patients, Messina et al. observed a possible role of oral antibiotic therapy for acute osteomyelitis [15].Data on the route and duration of oral antibiotic therapy for chronic osteomyelitis especially in the pediatric population are lacking [16].In the absence of a consensus on the route of administration and duration of therapy, intravenous antibiotic therapy for two to six weeks before transitioning to oral antibiotics for a total of four to eight weeks has been recommended [1,4].Duration of therapy of six weeks is recommended to allow for osteogenesis [4].Despite aggressive prolonged antimicrobial therapy and surgical debridement, relapse can occur as long as fve years later [12].

Conclusions
We describe the frst case of S. schleiferi chronic osteomyelitis in an immunocompetent adolescent.Our patient met the criteria for chronic osteomyelitis from the incomplete treatment of acute osteomyelitis.Te uncommon pathogen S. schleiferi was after canine exposure and may be emerging in human infections.Tus far, data on the pathogenesis and virulence of S. schleiferi in various human conditions including osteomyelitis are sparse.Treatment strategies for S. schleiferi chronic osteomyelitis included prolonged antimicrobial treatment and a multidisciplinary approach, similar to the guidelines for S. aureus osteomyelitis.Healthcare providers need to be familiar with the increase of uncommon microorganisms such as S. schleiferi and their antibiogram when involving prolonged antimicrobial treatment and the potential risk of antibiotic resistance.Despite the immediate recovery we are reporting, prolonged follow-up will enhance our understanding and knowledge of this microorganism due to the high relapse rate of chronic osteomyelitis.

Limitations
We report a single case highlighting the identifcation of an uncommon pathogen in a known medical condition.Tis descriptive study was a retrospective review of electronic medical record notes written by physicians in training and specialists, laboratory fndings, and imaging studies.Our 4 Case Reports in Infectious Diseases conclusions were inferred.More data regarding S. schleiferi as a pathogen in humans are needed.

Figure 1 :
Figure 1: Plain radiographs of the left tibia showed osseous destruction throughout on (a) anteroposterior view and (b) lateral view with the sinus tract (white arrow), sequestrum, and surrounding involucrum (yellow arrow).

Figure 2 :
Figure 2: Magnetic resonance imaging (MRI) with gadolinium enhancement of the left leg on (a) transverse view and (b) coronal view demonstrating intramedullary edema (yellow arrow) and the sinus tract (white arrow).