Exploring the antimicrobial efficacy of silver acetate against Acinetobacter baumannii and development of an in vitro biofilm model

Acinetobacter baumannii is a nosocomial pathogen with a remarkable capacity for antimicrobial resistance. This bacterial species possesses the ability to form biofilms and survive on abiotic surfaces within hospitals, which makes it a common cause of ventilator associated pneumonia, bacteraemia, catheter associated urinary tract infections , and wound and burn infections. As A. baumannii can cause catheter associated urinary tract infections via biofilm formation on catheters and silver acetate coated catheters are used commercially for prevention of infection, this thesis aimed to explore first the efficacy of silver acetate as an antimicrobial, and then to develop a modified Drip Flow Biofilm Reactor® tubing model to mimic biofilm formation within a catheter. A. baumannii NCTC 13302 was first determined to be the best biofilm forming strain out of the five isolates in the study, and it contained the OXA-24-like gene that provides carbapenem resistance. This strain was then utilised to test the minimum inhibitory concentration of silver acetate, its biofilm prevention capabilities, and its growth inhibitory effects. This provided raw data which did not exist for silver acetate against A. baumannii as there were no other studies stating the antimicrobial activity of silver acetate against this species. A further test of in vivo toxicity of silver acetate was carried out using Galleria mellonella larvae which validated the low toxicity of the silver salt. A further test where the larvae were infected with A. baumannii and then treated with silver acetate showed a significant increase in the survival of the larvae, showing the effectiveness of silver acetate as a treatment. The modified Drip Flow Biofilm Reactor® tubing model was developed first with A. baumannii NCTC 13302 in Mueller-Hinton Broth and subsequently with a modified Artificial Urine Media to move the model towards an imitation of a catheter associated urinary tract infection. During development, it was found that the most efficient way to assess biofilms grown within silicone tubing for five days was to run two samples in parallel and assess viability with cell counts and live/dead staining and to image with Scanning Electron Microscopy. The model developed herein will allow the study of A. baumannii biofilm formation on catheter tubing in conditions that begin to mimic the clinical environment. Future developments will focus on testing the antimicrobial activity of silver acetate coated catheter tubing against A. baumannii, and adaptation of the model to imitate bladder mechanics with a catheter fitted, which would provide a novel model to better study prevention of catheter associated urinary tract infections