Fulminant arterial vasculitis as an unusual complication of disseminated staphylococcal disease due to the emerging CC1 methicillin-susceptible Staphylococcus aureus clone: a case report

The patient was a 14-year-old male child without notable past medical history and no recent travel. On admission, he had fever, lethargy and diarrhea, and physical examination revealed fever (39 °C), tachycardia, blood pressure 65/35 mmHg and poor peripheral perfusion. Several boils were observed on the right elbow. He had subnormal white blood cell count 2.8 × 10⁹ / L with low lymphocyte count (13%), a moderate thrombocytopenia and raised CRP (347 mg/L) and procalcitonin plasma levels (279 ng/mL). The diagnosis of septic shock with a possible associated toxic mechanism was retained and intravenous (i.v.) cefotaxime and clindamycin were started with concomitant volume expansion. In the Intensive Care Unit, the patient was intubated as he became confused, needed norepinephrine, inotropic support by epinephrine, and required hemofiltration. Blood cultures showed methicillin susceptible S. aureus (MSSA) and treatment was switched to i.v. cloxacillin, clindamycin, and gentamicin. Complementary explorations revealed multiple septic pulmonary abscesses, an abscess of the left occipital lobe, and the absence of endocarditis. In view of septic emboli, clindamycin was switched to fosfomycin in order to have a better cerebral diffusion. The patient then developed ischemia of the four limbs without any purpuric lesion or signs of disseminated intravascular coagulation, which unfortunately rapidly progressed to dry gangrene of the left toes and of the right leg requiring amputation at day 11 after admission. The clinical status of the patient improved slowly. Catecholamines were stopped at day 6, the patient got extubated at day 11, and he recovered an efficient renal function 5 weeks after his admission. He had no serious neurological injury and a control cerebral MRI was normal three months later.

Our initial hypothesis underlying this atypical phenotype was the association of a vasospasm due to high doses of vasopressors and microcirculation disorders due to sepsis. We therefore analyzed the amputated specimen by light microscopy. Samples of left and right amputations were formalin fixed, paraffin embedded, and cut into 3 μm-thick sections. Sections were stained with Hematoxylin and Eosin, Gram, Periodic Acid Schiff and Grocott staining. The histopathologic analysis revealed perivascular infiltrates of mononuclear cells and neutrophils with arterial involvement (medium-sized vessels) without any capillary lesion (Fig. 1a and b). Furthermore, the arterial endothelium was destroyed and the walls were invaded by Gram-positive cocci with subsequent thrombosis (Fig. 1c and d).

In order to decipher mechanisms underlying these clinical and histopathological findings, pathogen virulence and host factors were analyzed. A whole-genome shotgun library was prepared with Nextera XT Kit (Illumina, San Diego, CA, USA) and sequenced on the MiSeq Illumina sequencing platform (2 × 150 bp paired-end reads). All reads were screened by mapping to known alleles of virulence genes using the Short Read Sequence Typing for Bacterial Pathogens program (SRST2) [8]. Virulence gene allele sequences were retrieved from the virulence factor database (VFDB, http://​www.​mgc.​ac.​cn/​VFs/​). SRST2 was also used to define the sequence type of the strain. Antibiotic-resistance predictions were performed directly from raw reads using “Mykrobe predictor S. aureus” tool [9]. All generated sequences are available at NCBI’s BioProject database under accession number PRJNA315766 (http://​www.​ncbi.​nlm.​nih.​gov/​bioproject/​PRJNA315766). The sequenced S. aureus isolate was a methicillin-susceptible strain harboring a staphylococcal cassette chromosome (SCC). The patient’s strain genome encoded numerous pathogenesis-related genes. The virulence gene equipment of the strain notably included several cytotoxin genes encoding the gamma-hemolysin and the Panton-Valentine (LukSF-PV), LukED and LukGH leukotoxins. It also included genes involved in adhesion and biofilm formation, genes encoding various enterotoxins (A, H, K, and Q) and superantigens, exoproteases and immune response evasion proteins (Table 1). The patient’s strain belonged to the clonal complex CC1-MSSA-SCCfus [PVL+].

Then, thrombophilic factors and immunity of the patient were examined. Initial low circulating protein antithrombin, C and S returned to normal after one month, and other factors associated with hereditary thrombophilia including activated protein C resistance, lupus anticoagulant and prothrombin G20210A mutation, were absent. Lymphocyte subsets of the patient were determined by routine flow cytometry, serum levels of the IgM, IgA, IgG, and IgG subclasses were assessed by standard nephelometry techniques, and complement was measured via enzyme-linked immunosorbent assay (ELISA). Activation of complement pathways was normal as well as B, T and NK lymphocyte cell count and immunoglobulin levels. Then, activation of cells in whole-blood of the patients were determined after granulocyte isolation by Ficoll density gradient centrifugation. Cells were activated with Toll like receptors agonists, stained with anti-CD62L-FITC, and analyzed by flow cytometry. In vitro stimulation of the patient’s peripheral blood mononuclear cells by LPS showed a standard production of cytokines IL-6 and IL-10 by ELISA.

Finally, functional common polymorphisms associated with severe infections and septic shock (PAI-1, rs1799768; MIF, rs755622; ACE rs17326674 IL6, rs1800795; TNF rs1800750, rs1800629, rs361525, and rs909253; TLR2, rs5743708 and rs5743704, TLR4, rs4986790; TLR5, rs5744168; IRAK1, rs1059703; IKB, rs2233406 and rs3138053; FCgammaRIIA, rs1801274 and CFH, rs1065489) [6, 7] were genotyped using TaqMan Single Nucleotide Polymorphism Genotyping Assays as previously described [7]. Genomic DNA was extracted from mononuclear cells using MagnaPure Compact automate (Roche Diagnostics®). The SNP genotyping revealed that the patient was homozygous for four potential deleterious variants of IRAK1, MIF, ACE, and PAI-I (Table 2).