Evaluation of Ceftaroline Alone and in Combination against Biofilm-Producing Methicillin-Resistant Staphylococcus aureus with Reduced Susceptibility to Daptomycin and Vancomycin in an In Vitro Pharmacokinetic/Pharmacodynamic Model

Abstract

Annually, medical device infections are associated with >250,000 catheter-associated bloodstream infections (CLABSI), with up to 25% mortality. Staphylococcus aureus, a primary pathogen in these infections, is capable of biofilm production, allowing organism persistence in harsh environments, offering antimicrobial protection. With increases in S. aureus isolates with reduced susceptibility to current agents, ceftaroline (CPT) offers a therapeutic alternative. Therefore, we evaluated whether CPT would have a role against biofilm-producing methicillin-resistant S. aureus (MRSA), including those with decreased susceptibilities to alternative agents. In this study, we investigated CPT activity alone or combined with daptomycin (DAP) or rifampin (RIF) against 3 clinical biofilm-producing MRSA strains in an in vitro biofilm pharmacokinetic/pharmacodynamic (PK/PD) model. Simulated antimicrobial regimens were as follows: 600 mg of CPT every 8 h (q8h) (free maximum concentration of drug [fCmax], 17.04 mg/liter; elimination half-life [t1/2], 2.66 h), 12 mg/kg of body weight/day of DAP (fCmax, 14.7 mg/liter; t1/2, 8 h), and 450 mg of RIF q12h (fCmax, 3.5 mg/liter; t1/2, 3.4 h), CPT plus DAP, and CPT plus RIF. Samples were obtained and plated to determine colony counts. Differences in log10 CFU/cm(2) were evaluated by analysis of variance with Tukey's post hoc test. The strains were CPT and vancomycin susceptible and DAP nonsusceptible (DNS). CPT displayed activity throughout the experiment. DAP demonstrated initial activity with regrowth at 24 h in all strains. RIF was comparable to the drug-free control, and little benefit was observed when combined with CPT. CPT plus DAP displayed potent activity, with an average log10 CFU/cm(2) reduction of 3.33 ± 1.01 from baseline. CPT demonstrated activity against biofilm-producing DNS MRSA. CPT plus DAP displayed therapeutic enhancement over monotherapy, providing a potential option for difficult-to-treat medical device infections.

FIG 1

In vitro PK/PD biofilm model results. (A) Strain R6067 (vancomycin-susceptible S. aureus [VSSA]). (B) Strain R6911 (hVISA). (C) Strain R6913 (VISA).

FIG 2

Confocal laser scanning microscopy analysis of coupons after 72 h in the in vitro PK/PD biofilm model for strain R6913. (A) Drug-free control, showing vast biomass with live cells. (B) Ceftaroline monotherapy, showing decreased biomass with live cells. (C) Ceftaroline plus daptomycin, showing minimal biomass with dead cells.

FIG 3

Activity of ceftaroline (CPT) plus daptomycin (DAP) in combination with static concentrations on biofilms growth on polyurethane coupons in a well plate assay with isolate R6913. (A) Viable remaining bacteria recovered in biofilm after 24 h growth on coupon. (B) SEM images of biofilm/bacteria eradication on the coupon. Shown are growth (no antibiotic) (left), CPT and DAP at the MIC (0.5 and 4 μg/ml, respectively) (middle), and CPT plus DAP at fC_max (17 μg/ml and 15 μg/ml, respectively) (right).