Presence of the neonatal Staphylococcus capitis outbreak clone (NRCS-A) in prosthetic joint infections

Abstract

Staphylococcus capitis is a coagulase-negative staphylococcus that has been described primarily as causing bloodstream infections in neonatal intensive care units (NICUs), but has also recently been described in prosthetic joint infections (PJIs). The multidrug-resistant S. capitis subsp. urealyticus clone NRCS-A, comprising three sublineages, is prevalent in NICUs across the world, but its impact on other patient groups such as those suffering from PJIs or among adults planned for arthroplasty is unknown. Genome sequencing and subsequent analysis were performed on a Swedish collection of PJI isolates (n = 21), nasal commensals from patients planned to undergo arthroplasty (n = 20), NICU blood isolates (n = 9), operating theatre air isolates (n = 4), and reference strains (n = 2), in conjunction with an international strain collection (n = 248). The NRCS-A Outbreak sublineage containing the composite type V SCCmec-SCCcad/ars/cop element was present in PJIs across three Swedish hospitals. However, it was not found among nasal carrier strains, where the less virulent S. capitis subsp. capitis was most prevalent. The presence of the NRCS-A Outbreak clone in adult patients with PJIs demonstrates that dissemination occurs beyond NICUs. As this clone has several properties which facilitate invasive infections in patients with medical implants or immunosuppression, such as biofilm forming ability and multidrug resistance including heterogeneous glycopeptide-intermediate susceptibility, further research is needed to understand the reservoirs and distribution of this hospital-associated pathogen.

Figure 1

Midpoint-rooted maximum-likelihood phylogeny of 305 S. capitis isolates based on 37,970 SNPs after purging of recombination. The Swedish isolates are represented by black dots. The colours in the main circle describe the setting where isolates were retrieved: yellow = air, green = community, blue = neonatal, red = PJI, purple = adult (unspecified location), brown = child (unspecified location). The subspecies differentiation of S. capitis is presented, as are the sublineages of S. capitis subsp. urealyticus. POBI proto-outbreak 1. POBII proto-outbreak 2. Scale bar indicates substitutions per site.

Figure 2

Midpoint-rooted maximum-likelihood phylogeny of 56 S. capitis isolates and presence of resistance genes based on a 75% core genome. Different centres are identified as c1–c4 and reference isolates named r1 (NRCS-A prototype strain CR01), r2 (CCUG 55892), and r3 (CCUG 35173). All isolates except r1 were isolated in Sweden. The settings where all Swedish strains were isolated are presented in colour: yellow = air, green = community, blue = neonatal, red = PJI, and white = no data. From c1 was included nasal isolates (n = 20), PJI isolates (n = 4) and NICU isolates (n = 3), from c2 operating theatre air (n = 4), from c3 PJI isolates (n = 12) and NICU isolates (n = 3) and from c4 PJI isolates (n = 5) and NICU isolates (n = 3). The phylogeny highlighted the subsp. capitis, Basal, and NRCS-A clade sublineages. Black blocks represent presence of genes mediating antibiotic resistance and SCCmec type.