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Antimicrobial Agents and Chemotherapy, October 2005, p. 4042-4045, Vol. 49, No. 10
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.10.4042-4045.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Comparative Efficacies of Quinupristin-Dalfopristin, Linezolid, Vancomycin, and Ciprofloxacin in Treatment, Using the Antibiotic-Lock Technique, of Experimental Catheter-Related Infection Due to Staphylococcus aureus

Institute of Infectious Diseases and Public Health, Università Politecnica delle Marche, Ancona, Italy,¹ Department of General Surgery, INRCA-IRRCS, Università Politecnica delle Marche, Ancona, Italy,² Experimental Animal Models for Aging Units, Research Department, INRCA-IRRCS, Ancona, Italy³

Received 17 May 2005/ Returned for modification 25 June 2005/ Accepted 24 July 2005

We performed in vitro studies to elucidate the bactericidal activity of the antibiotics in an adherent-cell biofilm model. Efficacy studies were performed in a staphylococcal central venous catheter (CVC) infection rat model. Silastic catheters were implanted into the superior cava. Via the CVC the rats were challenged with 1.0 x 10⁶ CFU of a live Staphylococcus aureus strain. Twenty-four hours later, the antibiotic-lock technique was started. All animals were randomized to receive daily isotonic sodium chloride solution, quinupristin-dalfopristin (Q/D), linezolid, vancomycin, or ciprofloxacin at the minimal bactericidal concentration (MBC) and at 1,024 µg/ml in a volume of 0.1 ml that filled the CVC. The main outcome measures were MICs and MBCs for both planktonic and adherent cells, quantitative culture of the catheters and surrounding venous tissues, and quantitative peripheral blood cultures. The killing activities of all antibiotics against the adherent bacteria were at least fourfold lower than those against freely growing cells, with the exception of Q/D, which showed comparable activities against both adherent and planktonic organisms. Overall, Q/D at 1,024 µg/ml produced the greatest reduction in the number of cells recovered from the catheters, while at the same concentration, Q/D and vancomycin demonstrated higher activities than ciprofloxacin or linezolid in reducing the number of organisms recovered from the blood cultures. This study points out that treatment outcome of device-related infections cannot be predicted by the results of a standard susceptibility test such as the MIC. Our findings suggest that the clinically used antibiotics cannot eradicate the CVC infection through the antibiotic-lock technique, even at a concentration of 1,024 µg/ml.

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