Background: Staphylococcus capitis has traditionally been considered a commensal due to its low pathogenicity in healthy adults; however, it has been shown to cause 20% of all cases of neonatal sepsis in neonatal intensive care units (NICUs). In addition, S. capitis strains with reduced susceptibility to last line anti-staphylococcal agents such as vancomycin and linezolid are emerging in NICUs. The aim of this study was to characterize S. capitis isolated from blood in a Swedish NICU and to investigate if the multidrug-resistant clone NRCS-A has disseminated in Sweden.
Materials/methods: All S. capitis isolates from neonatal blood cultures collected at Örebro University Hospital during 1987 to the 1st of March 2017 (n=42), were included. Several more episodes of neonatal sepsis with growth of coagulase-negative staphylococci were registered during this time period but probably considered as contaminants and therefore not preserved. Antibiotic susceptibility testing was performed using standardized disc diffusion method on cefoxitin, fusidic acid, clindamycin, erythromycin, gentamicin, rifampicin, trimethroprim/sulfamethoxazole and norfloxacin. Isolates resistant to ≥3 antibiotics were defined as multidrug-resistant. The isolates were whole genome sequenced using the Nextera XT kit (Illumina) on a MiSeq (Illumina). Single nucleotide polymorphisms found with the online tool REALPHY 1.12 in the alignments of shared homologous sites with the reference (the S. capitis NRCS-A strain CR01) were used to create phylogenetic trees.
Results: Seventeen isolates out of the 42 isolates (40%) were multidrug-resistant (resistant to fusidic acid, cefoxitin and gentamicin) and 33 out of the 42 isolates (79%) clustered with the multi-resistant NRCS-A clone (Figure 1). The earliest isolate within the NRCS-A cluster was from 2001.
Conclusions: Although prevalent since 2001, the increase of S. capitis in neonates with bacteremia since 2010 in Örebro county is mainly due to the dissemination of the multidrug-resistant NRCS-A clone and therefore warrants increased surveillance of the epidemiology and etiology of neonatal sepsis to prevent the spread of this clone.