# Postoperative Hardware-Related Infection fromKytococcus schroeteri: Its Association with Prosthetic Material and Hematological Malignancies—A Report of a Case and Review of Existing Literature

Authors: Aditya S. Shah; Prakhar Vijayvargiya; Sarah Jung; John W. Wilson
Journal: Case Reports in Infectious Diseases
 (2019)

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## Abstract

Introduction. Kytococcus schroeteri is an infrequently isolated Gram-positive coccus often encountered as a commensal bacterium. Only eighteen cases of human infection associated with this organism have been previously reported. Most of these cases involved patients with implanted prosthetic materials or patients with immunosuppressive conditions. It has been described in prosthetic valve endocarditis and in select patients with hematologic diseases but only one prior report as being involved in osteoarticular infections. Case Presentation. We describe a case of postsurgical osteoarticular hardware-related infection by K. schroeteri and discuss a possible association with implanted prosthetic material. Conclusion. Other clinical presentations of K. schroeteri, including reported infection syndromes, antimicrobial susceptibility profiles, and treatment outcomes, are also reviewed.


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## Body

## 1. Introduction

Kytococcus schroeteri is a Gram-positive coccus that was first identified by 16S rDNA analysis in 2002 [1]. It is a yellow-pigmented, aerobically growing, nonencapsulated, nonmotile bacterium. The natural habitat of K. schroeteri is not well defined, but other members of the genus Kytococcus (K. sedentarius) have been isolated from human skin. Human infection caused by this commensal bacterium is uncommon. The first case of K. schroeteri infection was described in 2002, in a patient with prosthetic valve endocarditis [1]. Over the subsequent sixteen years, 18 cases have been reported. Of those, only one prior case has been reported of K. schroeteri causing an osteoarticular infection [2]. We discuss a case of K. schroeteri associated with a postsurgical hardware-related infection and review its known role in other select infection syndromes.


## 2. Case Report

Our patient was an 80-year-old female with a history of chronic adrenal insufficiency on oral prednisone. She suffered a left-sided intertrochanteric hip fracture and underwent a surgical implantation of a cephalomedullary nail to stabilize the femoral neck. Over the next two weeks, she developed continuous drainage from the surgical incision. On presentation to the hospital, she had ecchymoses on her left flank and serosanguinous drainage from her left hip incision. She was afebrile on admission but had an elevated white blood cell count of 29 × 109/L. An ultrasound of the hip and groin region showed a hematoma and a large left groin pseudoaneurysm from the profunda femoral artery, which was confirmed by a CT angiogram. The patient underwent coil embolization of the pseudoaneurysm and surgical wound debridement.


### 2.1. Investigations and Diagnosis

There were multiple positive culture results forK. schroeteri on hip tissue/peri-joint tissue sent intraoperatively; and the treating infectious disease team with orthopedic infectious disease speciality focus felt this was real and constituted a prosthetic joint infection, warranting full treatment and suppression. This strain was resistant to penicillin but susceptible to clindamycin and vancomycin by Mueller–Hinton agar dilution.


### 2.2. Treatment

The patient was discharged to a care facility and received four weeks of daptomycin. This medication was chosen for out-of-hospital convenience of administration, owing to the once-a-day dosing. She recovered complete mobility of the joint and had no further complications in her course.


## 2.1. Investigations and Diagnosis

There were multiple positive culture results forK. schroeteri on hip tissue/peri-joint tissue sent intraoperatively; and the treating infectious disease team with orthopedic infectious disease speciality focus felt this was real and constituted a prosthetic joint infection, warranting full treatment and suppression. This strain was resistant to penicillin but susceptible to clindamycin and vancomycin by Mueller–Hinton agar dilution.


## 2.2. Treatment

The patient was discharged to a care facility and received four weeks of daptomycin. This medication was chosen for out-of-hospital convenience of administration, owing to the once-a-day dosing. She recovered complete mobility of the joint and had no further complications in her course.


## 3. Discussion

The increasing number of case reports, including our own, suggests thatK. schroeteri can be a formidable pathogen in the appropriate host. The significance of Kytococcus as a human pathogen may not have been fully recognized in years past or previously misidentified as Micrococcus sp. Recent case reports have been able to identify this organism by molecular sequencing or using matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry (MALDI-TOF MS) technology, as in our case. The organism grew on a blood agar plate (a trypticase soy agar plate with 5% sheep’s blood) at 35° Celsius in a CO2-enriched environment. Colony growth showed muddy yellow-pigmented bacteria. In this report, we identify a case where Kytococcus was isolated from bacterial cultures and was implicated in a postsurgical hardware-related infection.To our knowledge, this is the second known report of an osteoarticular infection caused byK. schroeteri. The first known case of orthopedic infection caused by this organism was described in a case of spondylodiscitis after surgery [2]. Our patient was moderately immunocompromised as she was taking prednisone 10 mg daily for several years for her chronic adrenal insufficiency. Our review of the literature (Table 1) identified 13 other cases (Table 1) with Kytococcus infection that were associated with implanted foreign material: eight with prosthetic valve endocarditis, two with VP shunt infections, one with prosthetic discitis, one with silicon tendon graft infection, and one with medullary nail infection (our patient). These reports underscore the importance of evaluating for foreign body infections in patients who have a positive blood culture with K. schroeteri.Table 1
Reported cases ofKytococcus infection.
Age (years)/Sex
Immunocompromising condition
Primary source of infection
Therapy
Outcome
Report
34/F
None
Prosthetic valve endocarditis
Vancomycin, rifampin, and gentamicin
Recovered
Becker et al. [1]
71/F
Asthma on chronic prednisone therapy
Pneumonia/bacteremia
Ceftriaxone and ofloxacin
Deceased
Mohammedi et al. [3]
73/M
None
Prosthetic valve endocarditis
Teicoplanin, rifampin, and gentamicin
Recovered
Le Brun et al. [4]
49/F
None
Prosthetic valve endocarditis
Vancomycin and gentamicin, followed by pristinamycin and vancomycin
Recovered
Mnif et al. [5]
38/F
None
Prosthetic valve endocarditis
Vancomycin and gentamicin, followed by levofloxacin and rifampin
Recovered
Aepinus et al. [6]
70/M
None
Prosthetic valve endocarditis
Amoxicillin and gentamicin
Recovered
Renvoise et al. [7]
1/M
None
VP shunt
Vancomycin and rifampin
Recovered
Jourdain et al. [8]
72/M
None
Prosthetic valve endocarditis
Vancomycin, rifampin, and gentamicin
Recovered
Poyet et al. [9]
64/M
None
Prosthetic valve endocarditis
Vancomycin, rifampin, and gentamicin
Recovered
Yousri et al. [10]
50/F
Type 2 diabetes
Prosthetic discitis
Ofloxacin and rifampin
Recovered
Jacquier et al. [2]
40/M
Acute myeloid leukemia
Pneumonia/bacteremia
Vancomycin, rifampin, and gentamicin
Deceased
Hodiamont et al. [11]
52/M
Acute myeloid leukemia
Pneumonia/bacteremia
Vancomycin and ceftazidime
Deceased
Hodiamont et al. [11]
43/F
Acute myeloid leukemia
Pneumonia and bacteremia
Vancomycin/piperacillin/tazobactam, vancomycin/meropenem, and linezolid, discharged on TMP/SMX
Recovered
Blennow et al. [12]
68/M
Acute myeloid leukemia
Pneumonia and bacteremia
Vancomycin
Deceased
Nagler et al. [13]
45/M
None
Silicone tendon graft
Oral doxycycline
Recovered
Chan et al. [14]
53/M
None
Prosthetic valve endocarditis
Daptomycin
Recovered
Liu et al. [15]
3/F
Ganglioma
VP shunt
Cefuroxime and gentamicin
Recovered
Schaumburg et al. [16]
51/F
Hairy cell leukemia
Pneumonia and bacteremia
Vancomycin and piperacillin/tazobactam
Deceased
Amaraneni et al. [17]
80/F
None
Medullary nail
Daptomycin
Recovered
Shah et al. 2017Our literature review also identified 6 reported cases ofKytococcus pneumonia. Five of these were in conjunction with hematological malignancy (4 AML and 1 hairy cell leukemia) [11–13, 17]. The sixth patient had no hematologic condition but was moderately immunocompromised by taking prednisone 20 mg daily for 2 years for management of refractory asthma [3]. Indeed, at our institution, we have also encountered a separate and additional patient with acute myelogenous leukemia who developed fever, hypoxic respiratory failure, and consolidated infiltrates on chest imaging. K. schroeteri was identified in multiple cultures from respiratory samples (unpublished).K. schroeteri is frequently misidentified as Micrococcus sp. because of similar morphological features. However, a distinction between the two is important since Micrococcus sp. is inherently susceptible to penicillin and oxacillin, whereas Kytococcus sp. is not. Antimicrobial susceptibility testing (AST) of K. schroeteri from both our patients demonstrated in vitro resistance to penicillin and susceptibility to vancomycin and clindamycin. We also reviewed the antimicrobial susceptibility testing (AST) profile from all prior cases associated with this organism (Table 1), and the characteristic resistance to penicillin and susceptibility to vancomycin were uniform.An important point to highlight is the fact that there are no formal established MIC breakpoints by the Clinical Laboratory Standards Institute (CLSI); therefore, the laboratory interpretation of MIC breakpoints reflecting drug susceptibility vs. resistance are implied and must be interpreted with caution. In 2015, CLSI did publish MIC breakpoints forMicrococcus sp. Several genera, including Kytococcus sp., have been included under the Micrococcus group for AST interpretation. While CLSI defines clinical “susceptible” vs. “resistant” Micrococcus MIC breakpoints for penicillin, there is no formal “resistant” MIC breakpoint defined for vancomycin. Rather, only an MIC breakpoint below which vancomycin susceptibility is reported. Therefore, vancomycin resistance is implied when reported at or above the MIC breakpoint. Whether there are clinically relevant MIC breakpoint differences between Micrococcus and Kytococcus has not been adequately determined at this time. An AST database of Kytococcus and Micrococcus isolates by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) has been developed at our center to augment the currently available CLSI reporting standards.In summary, we describe the second known case of an osteoarticular infection fromK. schroeteri and reviewed the published reports of K. schroeteri disease. While often considered part of the natural skin bacterial flora, human infections with K. schroeteri do occur and have presented in patients with infected implanted prosthetic material and as respiratory infections in patients with significant immunosuppressive conditions, including select hematologic malignancies. Kytococcus appears to be susceptible to vancomycin and resistant to penicillin when grouped with Micrococcus by CLSI, although species-specific MIC breakpoints have not yet been formally established. The advancements made in laboratory diagnostic techniques along with rising applications of prosthetic materials may collectively enable an increased awareness of Kytococcus sp. as a potentially formidable human pathogen. Early identification and appropriate treatment will be critical toward successful outcomes.



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