Staphylococcus epidermidis are important opportunistic biofilm forming pathogens, particularly causing infection in patients with indwelling medical devices. Preterm infants represent a high-risk group for device-related S. epidermidis infections since they require the delivery of nutrients and drugs over long periods.
The present study compared genetic and phenotypic characteristics of S. epidermidis strains isolated from blood stream infections of preterm infants (n=10) versus skin isolates obtained from healthy newborns (n=16). Two reference strains were also included the study. Insertion element IS256, as a marker for invasiveness, was analysed by PCR. Antimicrobial susceptibility was testing against cefoxitin, gentamicin and vancomycin. Pulsed-Field Gel Electrophoresis was performed to study clonal relationship among strains.
90% of the blood isolates were resistant to cefoxitin and gentamicin and all these carried IS256. All skin isolates were susceptible to both cefoxitin and gentamicin and all lacked IS256. All of the 28 strains included in the study were susceptible to vancomycin.
We conclude that the S. epidermidis strains isolated from blood stream infection in preterm infants are clonally not related to the normal colonizing S. epidermidis skin flora at birth, have different phenotypic features related to antimicrobial susceptibility, and have most probably originated from the hospital environment.