case report

: Background: Staphylococcus saccharolyticus is a rarely encountered coagulase-negative slowly grower and strictly anaerobic staphylococcus from the skin. It is usually considered as a contaminant, but some rare reports describe deep-seated infections. Virulence factors remain poorly known although genomic analysis highlight pathogenic potential. Case presentation: we report a case of Staphylococcus saccharolyticus spondylodiscitis that followed kyphoplasty, a procedure associated with a low rate of sometimes severe infectious complication (0.46%) and we reviewed the literature. This case specifically stresses the risk of S. saccharolyticus health-care associated infection in patients of poor condition. Conclusion: infection to S. saccharolyticus is difficult to diagnose due to microbiological characteristics of this bacterium, requires timely treatment and improved infection control procedure should be encouraged for patients with poor condition.


Background:
Staphylococcus saccharolyticus(formerly Peptococcus saccharolyticus) is a rarely encountered coagulase-negative staphylococcus and the only anaerobic species of the genus Staphylococcus [1]. While it is usually considered as a non-pathogenic microorganism of the human skin flora with no particular known tropism to generate specific infections, occasional reports suggest a pathogenic potential through miscellaneous rare deep-seated infections [2][3][4][5]. Little is known on its virulence factors, pathogenesis and determinants of infection. Recently, genome sequencing analysis has shown that S. saccharolyticus carries hyaluronidase activity (similar to that of Staphylococcus aureus), toxins of the phenol-soluble modulin family and several quorum sensing systems that may provide a tissue-invasive potential [6].
Infectious complications after vertebroplasty/kyphoplasty are rare but potentially serious complications that can be life-threatening or affecting the patient's functional prognosis, (0.46%) and usually result from direct inoculation from skin flora such as Staphylococcus aureus, S. epidermidis, Cutibacterium acnes, etc. [7,8]. Here, we report the third case of spondylodiscitisdue to S. saccharolyticus, and the first one thatfollowed a surgical procedurelike kyphoplasty that specifically stresses the risk of S. saccharolyticus health-care associated infection [2,3].

Case presentation:
A57-year-old man with a history of alcoholism and heavy smoking was admitted for disabling back pain. Four months earlier, a fall induced two vertebral fractures (T10, T11) treated by kyphoplasty under CT-scan guidance. Because the back pain persisted two weeks after the procedure, he received a zygapophyseal joint steroid injection under CT-guidance. Three days later C-reactive protein level was 12.5 mg/l, hyperleukocytosis was moderate (13 G/L including 10G/L neutrophils) and the patient had no fever. Magnetic Resonance Imaging was consistent with infectious spondylodiscitis (Figure 1a). A Staphylococcus saccharolyticus isolate was recovered after 90 hours of incubation from one single vial of a first series of three blood culture (BC) sets. The same microorganism was recovered from two additional BC series collected five and ten days later, after respectively 83 and 100 hours of incubation.
These findings fulfilled the criteria for a definite diagnosis of spondylodiscitis while the patient had neither catheter nor spine device. Using disk diffusion assay, the isolate was multi-drug susceptible including to penicillin and cefoxitin. The patient was treated with 2 g of amoxicillin three times a day for a total duration of 4 weeks after consultation with the infectious disease team. Pain and inflammatory syndrome both gradually regressed and MRI performed month 12 showed decrease of hyperintensity ( Figure 1b). No clear source of the bacteria was identified. It was presumably from skin and the bacteria was likely introduced in the surgical site during the kyphoplasty procedure. We could identify neither any defect in the surgical skin preparation and infection control procedures nor any particular event during the kyphoplasty procedure.

Discussion:
S. saccharolyticus is a little known coagulase-negative staphylococcus [1]. While it is usually considered as a skin contaminant, it is able to cause e.g., endocarditis, bone infection or pyomyositis, some of them with poor outcome (Table 1) [2][3][4][5][9][10][11][12][13].In addition to the tissue-invasive factors that have been unraveled, the dependence on anaerobic conditions is considered to inherently favor the ability to invade human tissue while biofilm production may contribute to colonize medical devices [6]. Further research is needed to better understand S. Saccharolyticus virulence and the risk of infection. In this regard, reports should also better consider patient comorbidities as host condition may play a role. So far, only 3 out of the 9 reported cases detailed host risk factors (Table 1).
To date, only three case of spondylodiscitis have been reported (including our case), of which 1 has been related to a surgical procedure and multiple levels diskographies [3], the current case occurred after kyphoplasty, while the third case [2] retrieved no information on surgical procedure. Both symptomatology and biological syndrome may be moderate or absent in the early stage of infection [4]. In our case, fever was absent and the inflammatory biologic syndrome was mild. Possible reasons could be the proximity of a corticosteroid injection, and effective empirical treatment that was timely administered. S.saccharolyticus is, in addition of being anaerobic, a slowly grower which may be misinterpreted as a contamination (long BC time-to-positivity, isolatedanaerobic -positive bottle) [1,9].This may also lead to under diagnosis, when cultures are not incubated at least 5 days, a regular situation with analyses other than BC.
The favorable evolution after appropriate antibiotics treatment is not a regular option.
The rare reported infections (9 to our knowledge) have often been fatal (3 out of the 7 available outcomes, (Table 1).Timely treatment may be critical. Comorbidities favoring opportunistic organisms to cause infection are unevenly reported: prosthetic heart valves (10,13), poor oral hygiene (2), type II diabetes (5), to which we can add important tobacco use, alcoholism and cachexia in this patient Last but not least, infection control procedures designed to prevent infection following vertebroplasty procedure may require some advance to improve infection prevention in patients with poorer condition.

Conclusion
The incidence of spondylodiscitis by S. saccharolyticus is reportedly low, but clinicians must not fail the diagnosis. We advise that any S. saccharolyticus culture in the context of fever and/or orthopedic pain should be cautiously reviewed before being considered as a contaminant. Prompt diagnosis and treatment is essential for an improved outcome of this severe infection and overall efforts should be made in infection control during vertebroplasty.

Ethics approval and consent to participate
Written consent was obtained from the patient. No ethics committee was necessary for this case report.

Consent for publication:
Written consent was obtained from the patient for publication of this case report. A copy of the written is available for review by Editor in Chief of this journal.
Availability of data and materials: Not applicable. Please contact authors for data requests Competing interests: The authors declare that they have no competing interests