Development of a novel antibacterial silver nanocoating to reduce nosocomial infections

Abstract

Nosocomial infections (those that are hospital-acquired) lead to patient morbidity and mortality, and are further complicated by the growing problem of antimicrobial resistance. Wastewater plumbing systems (WPS) are bacterial reservoirs and vehicles for bacterial transmission. Sink traps form a barrier between users and the WPS, but breaches can lead to contamination and have been implicated in outbreaks of infections. This project sought to address the need for a novel antimicrobial nanocoating to reduce bacterial colonisation and biofilm formation in sink traps.

A nanocoating was developed by embedding silver nanoparticles in a matrix of commercially-available and low-cost pipe cement, applied to unplasticised polyvinyl chloride. Material characterisation and nanotopography imaging revealed that roughness was increased by surface grinding, with nanotopography images showing the troughs produced, and high silver stability was evident with very low dissolution under controlled dialysis experiment conditions.

Culture-dependent and -independent techniques were used to characterise the bacteria present in hospital sink traps, revealing certain dominant genera such as Citrobacter, Pseudomonas and Serratia. Sequencing of 16S rDNA from sink traps has previously been an under-reported area. A bacterial isolate of interest, Cupriavidus pauculus MF1, was further investigated and found to be multidrug-resistant with biofilm formation comparable to Pseudomonas aeruginosa. Whole genome sequencing, producing a hybrid assembly of short- and long-reads, allowed annotation of a number of antibiotic and metal resistance and virulence factor genes of interest, supporting the suggestion that awareness should be increased for this and other opportunistic pathogens in hospital sink traps.

Silver nanocoatings demonstrated potent antiplanktonic and antibiofilm activity against the nosocomial pathogens Pseudomonas aeruginosa, Acinetobacter baumannii and Enterococcus faecalis.

Novel, more realistic experimental conditions were developed, first using a hospital sink trap community to colonise a benchtop model sink trap system. Antibiofilm activity was evident over long time periods, up to 11 days, but waned by day 25. Placement of silver nanocoated specimens in real-world sink traps in two university buildings provided little overall evidence of a consistent antibiofilm effect. Follow-up in vitro experiments using hospital and university building sink trap communities confirmed that the silver nanocoating was active against those same polymicrobial communities. It is possible that certain realistic environmental conditions mask the surface of nanocoatings and limit their activity, with relevance to antimicrobial nanocoating development in plumbing systems and other environments. The results indicate that there can be significant discord between in vitro and in situ experiments, emphasising the need for novel antimicrobial nanocoatings to be evaluated in real-world settings.