Abstract
Titanium (Ti)-based implants are broadly applied in the medical field, but their related infections can lead to implant failure. Photo-irradiation of metal materials to generate antimicrobial agents, an alternative to antibiotics, is a promising method to reduce bacterial infection and antibiotic usage. It is therefore important to understand how bacterial pathogens respond to Ti surfaces. Here, Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus, the most prevalent pathogens linked to healthcare-associated infections, were used as model strains. Two different kinds of Ti surfaces respectively stored in dry condition and 0.9 % NaCl solution were applied. Upon UV irradiation and in the absence of bacteria, both tested surfaces exhibited similar bactericidal activity, even though the surfaces stored in 0.9 % NaCl solution generated a slightly higher level of reactive oxygen species (ROS). Interestingly, P. aeruginosa and S. aureus responded to the irradiated Ti surfaces differently regarding interaction time: the number of viable P. aeruginosa was reduced up to 90 % after 30 min interaction with the treated surfaces compared to the untreated ones, but this reduction is lessened to 69 %–81 % after 240 min. By contrast, UV treatment of surfaces did not impact the viability of S. aureus after 30 min interaction, however, led to more than 99 % reduction after 240 min incubation. These results provide first experimental evidence that Gram negative and positive bacterial species respond to ROS with different inactivation kinetics. This work also demonstrated that treatment with photo-irradiation in the absence of bacteria conferred Ti surfaces with efficient bactericidal activity.
Highlights
Antimicrobial resistance poses an increasing threat to the health of human beings [1,2,3]
P. aeruginosa and S. aureus responded to the irradiated Ti surfaces differently regarding interaction time: the number of viable P. aeruginosa was reduced up to 90 % after 30 min interaction with the treated surfaces compared to the untreated ones, but this reduction is lessened to 69 %–81 % after 240 min
The novelty of this work lies in the demonstration that UV radiation without bacteria, still confers bacteri cidal activity to Ti surfaces, and for the first time, we provide experi mental evidence that Gram positive and negative bacteria show different inactivation kinetics in response to reactive oxygen species (ROS)
Summary
Antimicrobial resistance poses an increasing threat to the health of human beings [1,2,3]. Surfaces are modified to release antimicrobial agents, which can cause critical problems such as chemical toxicity, antimicrobial durability and resistance [7]. Contact-killing surfaces use either strongly incorporated antimicrobial substances e.g. polyphenols [8], quaternary ammonium [9] or micro/nanoscale surface topographies to confer antibacterial activity [10,11]. The long-term antibacterial activity is the main concern since killed bacterial cells can form a fouling layer and allow viable bacteria to adhere and grow. Alternatives are urgently needed, particu larly for implants, which normally have intimate contact with tissues. To this end, various coatings as mentioned above have been developed to prevent bacterial colonization on implant surfaces [5,12]
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