Catheter Colonization and Abscess Formation Due to <em>Staphylococcus epidermidis</em> with Normal and Small-Colony-Variant Phenotype Is Mouse Strain Dependent

<div><p>Coagulase-negative staphylococci (CoNS) form a thick, multilayered biofilm on foreign bodies and are a major cause of nosocomial implant-associated infections. Although foreign body infection models are well-established, limited <em>in vivo</em> data are available for CoNS with small-colony-variant (SCV) phenotype described as causative agents in implant-associated infections. Therefore, we investigated the impact of the <em>Staphylococcus epidermidis</em> phenotype on colonization of implanted PVC catheters and abscess formation in three different mouse strains. Following introduction of a catheter subcutaneously in each flank of 8- to 12-week-old inbred C57BL/6JCrl (B6J), outbred Crl:CD1(ICR) (CD-1), and inbred BALB/cAnNCrl (BALB/c) male mice, doses of <em>S. epidermidis</em> O-47 wild type, its <em>hemB</em> mutant with stable SCV phenotype, or its complemented mutant at concentrations of 10⁶ to 10⁹ colony forming units (CFUs) were gently spread onto each catheter. On day 7, mice were sacrificed and the size of the abscesses as well as bacterial colonization was determined. A total of 11,500 CFUs of the complemented mutant adhered to the catheter in BALB/c followed by 9,960 CFUs and 9,900 CFUs from <em>S. epidermidis</em> wild type in BALB/c and CD-1, respectively. SCV colonization was highest in CD-1 with 9,500 CFUs, whereas SCVs were not detected in B6J. The minimum dose that led to colonization or abscess formation in all mouse strains was 10⁷ or 10⁸ CFUs of the normal phenotype, respectively. A minimum dose of 10⁸ or 10⁹ CFU of the <em>hemB</em> mutant with stable SCV phenotype led to colonization only or abscess formation, respectively. The largest abscesses were detected in BALB/c inoculated with wild type bacteria or SCV (64 mm² vs. 28 mm²). Our results indicate that colonization and abscess formation by different phenotypes of <em>S. epidermidis</em> in a foreign body infection model is most effective in inbred BALB/c followed by outbred CD-1 and inbred B6J mice.</p>