Vertebral osteomyelitis secondary to a S. schleiferi infection from a cardiac defibrillator

Coagulase-negative staphylococci (CoNS) accounts for 31% of nosocomial bloodstream infections.^1–3 Normally, the course is subtle and non-specific without fulminant signs of infection, however, frank sepsis and fatal outcome may occur, especially in immunocompromised patients and/or if one of the more virulent species is involved.¹Staphylococcus schleiferi were described by Freney⁴ and have been reported in nosocomial infections.^1,2,5

An 82-year-old male presented with a 4-week history of asthenia, stiffness in the pelvic girdle and back pain, which begun insidiously and progressively worsened until compromise his walking ability. Due to symptoms of mild cardiac failure, he was readmitted 3-weeks later. He complained of persistent back pain and the physical examination revealed local tenderness to gentle spinal percussion and reduced back mobility with protective spasm of nearby muscles. His medical history included hypertension, diabetic mellitus, idiopathic dilated cardiomyopathy with implantable cardioverter defibrillator (ICD) placed 3 years ago and a psoas abscess by S. schleiferi treated with cloxacillin 2 g/4 h during 6 weeks 2 years before. Laboratory studies demonstrated leukocytosis (12,200/uL) with neutrophilia (10,492/μL) and elevations of erythrocyte sedimentation rate (ESR: 81 mm/h) and C-reactive protein (CRP: 77.4 mg/L). Bone radiography showed destructive changes of L3/L4 vertebral bodies with collapse of the intervening disc space and computed tomography (CT) reported abnormal thickening of the cortical bone of L3/L4 vertebral bodies, with sclerotic changes, end plate irregularities and disc flattening. Blood cultures and the material obtained via needle biopsy by CT guidance from the vertebral lesions yielded S. schleiferi susceptible to commonly used antibiotics. He was given cloxacillin 2 g/4 h and rifampicin 600 mg daily. A transthoracic echocardiogram did not demonstrate any vegetation. A positron emission tomography revealed pathological captation in the ICD cable; 3-weeks after the start of antimicrobial therapy, he was scheduled for ICD explantation, whose cable was cultured and it yielded S. schleiferi. He received another 4 weeks of intravenous antibiotic, switched to oral therapy with levofloxacin 750 mg/day and rifampicin 600 mg/day, and attained a complete clinical recovery with decreased levels of CRP (2.3 mg/L) and ESR (31 mm/h) at follow-up. He completed a 16-week antimicrobial therapy on account of severe vertebral disease as CT evidenced.

There are many reports of S. schleiferi as an infective pathogen, including bacteremia,² surgical site infections,² sternal osteomyelitis,⁶ prosthetic infections,⁵ brain empiema⁵ and pacemaker infections,⁷ nevertheless, this case is the first confirmed case of vertebral osteomyelitis. The frequency of these infections is extremely low compared with those caused by other species such as S. aureus or S. epidermidis,⁵ but it appears to play a particular and underestimated role in infectious colonization of implanted biomaterials due to erroneous identification of S. schleiferi as S. aureus⁶ because both species produce β-haemolysin and a heat-stable DNase.² Also, S. schleiferi subsp. coagulans produces coagulase, making more difficult the differentiation. This subspecies was first isolated from dogs suffering from external ear otitis, since then it has been reported in a surgical wound infection of the finger, in a disseminated human infection in an immune compromised host⁸ and in a left ventricular assist device infection in a patient awaiting heart transplantation.⁹ When analyzing other six cases of pacemaker infection,^7,10 the interval between pacemaker implantation and infection varied between 6 weeks and 16 months, with a median of 10–12 months. In the present report, the infection remained latent during 12 months, then it expressed with a psoas abscess and 24 months later with a vertebral osteomyelitis when we discovered the ICD infection, revealing an insidious course and leading to a delayed diagnostic.

In summary, it is important to perform a careful identification of S. schleiferi and it should be regarded as an important opportunistic pathogen, particularly in pacemaker-related infections,⁷ in which it is necessary to remove the device to avoid recurrences. In addition, it is essential to perform an appropriate preoperative preparation of the skin in view of the possible role of the axillary flora.^7,10