Evaluation of linezolid, vancomycin, gentamicin and ciprofloxacin in a rabbit model of antibiotic-lock technique for Staphylococcus aureus catheter-related infection.

BACKGROUND: The effectiveness of linezolid, vancomycin, ciprofloxacin and gentamicin for treating experimental Staphylococcus aureus catheter-related infection by the antibiotic-lock technique was assessed.

METHODS: Two methicillin-susceptible (MSSA) ATCC strains and two methicillin-resistant (MRSA) clinical strains were used. New Zealand white rabbits were surgically implanted with a silicone intravenous catheter. Infection was induced by filling and locking the catheter with 0.3 mL of broth culture containing S. aureus, with turbidity equivalent to that of a 0.5 McFarland standard. Eighteen hours later the antibiotic-lock technique was started and continued for 24 h. Treatment groups were: control without treatment; 2000 mg/L linezolid; 2000 mg/L vancomycin; 2000 mg/L ciprofloxacin; and 40,000 mg/L gentamicin.

RESULTS: Linezolid and vancomycin showed equivalent activity, achieving significant reductions in log(10) cfu recovered from catheter tips in one MSSA strain (>1.12) and one MRSA strain (>0.77) as compared with controls (P < 0.05). Ciprofloxacin achieved significant log(10) cfu reductions in MSSA strains relative to controls (>2.51, P < 0.01). In one MSSA strain, ciprofloxacin showed a larger reduction in log(10) cfu than linezolid or vancomycin (P < 0.01). Gentamicin was the only antibiotic achieving negative catheter tip cultures (up to 87.5% in MSSA and up to 40% in MRSA, P < 0.01), and showed the greatest log(10) cfu reduction compared with controls (>4.25 in MSSA and >2.93 in MRSA, P < 0.05) and significant differences relative to the remaining treatment groups (P < 0.05 in both MSSA and MRSA).

CONCLUSIONS: Gentamicin showed the highest activity against both MSSA and MRSA biofilms.