Staphylococcus epidermidis colonization is highly clonal across US cardiac centers

Abstract

Background: Little is known about the clonality of Staphylococcus epidermidis in the United States, although it is the predominant pathogen in infections involving prosthetic materials, including ventricular assist devices (VADs).

Methods: Seventy-five VAD recipients at 4 geographically diverse US cardiac centers were prospectively followed up to 1 year of VAD support. The anterior nares, sternum, and (future) driveline exit site were cultured for S. epidermidis before VAD insertion and at 7 times after surgery. Infection isolates were also collected. Isolates were typed by pulsed-field gel electrophoresis. A subset underwent susceptibility testing and staphylococcal chromosomal cassette mec and multilocus sequence typing.

Results: A total of 1559 cultures yielded 565 S. epidermidis isolates; 254 of 548 typed isolates (46%) belonged to 1 of 7 clonal types as defined by pulsed-field gel electrophoresis. These clones were identified in up to 27 people distributed across all 4 cardiac centers. They caused 3 of 6 VAD-related infections. Disseminated clones were more antibiotic resistant than were less prevalent isolates (eg, 79% vs 54% methicillin resistant; P = .0021).

Conclusions: This study revealed that healthcare-associated S. epidermidis infection is remarkably clonal. We describe S. epidermidis clones that are highly resistant to antibiotics distributed across US cardiac centers. These clones may have determinants that enhance transmissibility, persistence, or invasiveness. Clinical Trials Registration. NCT01471795.

Figure 1.

Analysis of multilocus sequence typing data with goeBURST (http://goeburst.phyloviz.net). This figure includes all available data in the database (www.mlst.net) as of 25 October 2011. Predicted founders of each clonal complex are shown in light green. Subgroup founders are depicted in dark green. Single-locus variants are shown in blue. Dark circles indicate sequence types that were identified in this study.

Figure 2.

Similarity of pulsed-field gel electrophoresis (PFGE) macrorestriction profiles of representative US Staphylococcus epidermidis isolates and isolates collected internationally. Strain names, geographical origin, relevance (infection [I] or colonization [C]), SCCmec type, and sequence types (STs) are shown. A dendrogram was performed to compare the PFGE profiles using Bionumerics software. e-BURST was used to assess clonal complexes (www.mlst.net). *mec complex/ccr type; ^All isolates belonged to clonal complex 5 (CC5). Abbreviation: NT: nontypable.