Investigation of existing and novel therapeutics to treat intravascular catheter-related infections caused by staphylococci using a combination of in vitro and animal models

Staphylococci are a leading cause of catheter-related infections (CRI). To reduce rates of these infections, catheter-locking solutions (CLSs) are frequently used. However, an effective CLS against these biofilm mediated infections has yet to be determined. The purpose of this study was to evaluate the efficacy, of currently available antiseptics, antibiotics as well as two novel antimicrobials, ML:8 and Citrox, as CLSs against staphylococcal biofilm.

Two distinct assays were used for analysing each agent; one widely used assay using enriched growth media and one newly developed assay using minimal media and a preconditioning coating of human plasma. Static and flow models of staphylococcal biofilm formation were used to examine the effect of the test agents. Ethanol (30%) and TaurolockTM proved to be the most effective antiseptic agents, against established biofilms. In contrast, antibiotics were shown to have little effect on established biofilm in the enriched media assay. However, daptomycin, rifampicin and tigecycline all showed increased efficacy against biofilm viability when the minimal media assay was used. These findings were confirmed by confocal microscopy and live/dead staining.

The novel agents ML:8 (1%), containing caprylic acid, and Citrox (1%), comprising of flavonoids, proved to be also effective against established biofilms. Cytotoxicity testing using THP-1 and HaCat cells indicated that both agents had minimal toxicity. No resistance to either agent, developed in S. aureus after 90 days exposure to both of these novel agents. Finally, ML:8 was shown to be effective against early stage S. aureus biofilm, while Citrox was shown to eradicate mature biofilm in a rat CRI model. Analysis of the bacterial transcriptional response to both novel agents revealed a decrease in expression of genes associated with adherence and genes encoding bacterial exoenzymes, while expression of toxin genes was both up- and down-regulated. Taken together, these data reveal the optimum currently available antiseptic and antibiotic agents to treat staphylococcal biofilm within a CLS and the efficacy of the novel antimicrobials ML:8 and Citrox within this model of infection.