Tackling Microbial Contamination: Safesink Solution with Silver-Coated Microspheres

Comments 1:

In this study, silver was coated on glass beads to produce bioactive silver glass beads with bactericidal activity. The application of the silver glass beads is not clearly mentioned in the manuscript, however, based on the introduction section, it is believed that the silver glass beads are intended as coating in medical devices for implantation.  First, the authors should clearly state the intended application of the silver glass bead as well as the need for this product in comparison with clinically used antimicrobial agent coated implants /medical devices. The authors should discuss the efficacy as well as the limitations of published studies especially for silver coated medical devices.

Response 1:

Thank you for pointing this out because it may not be clearly mentioned. In the abstract and introduction of the article, there are some references to the application of these silver-coated glass beads with bactericidal effect.  This application comes in response to a problem that occurs quite commonly in hospital facilities. These microspheres are designed to be included in siphons and water end points to prevent nosocomial infections occurring in hospital environments. The material is not designed for implants or medical devices. Although this type of application is not excluded in future research.

Comments 2:

For the silver release study, it is conducted with mechanical agitation for a controlled time of 30 minutes and continued until lixiviation time of 5 hours (10 extractions) was reached. Please state the rpm of the mechanical agitation that is used. Please state the limit of detection and limit of quantification for silver.

Response 2:

The mechanical agitation was performed at 400 rpm to simulate the movement of the glass beads in a siphon when in contact with water. We have revised the comment and will enter the data on line 139 and 269.

The limit of detection and limit of quantification for silver in ICP-OES measurements is 0.01 and 0.03 mg·Kg^-1 respectively. We will introduce this information in line 281.

Comments 3:

Please provide the homogeneity data.

Response 3:

We would need more details about the information you are requesting.

Comments 4:

As for the antibacterial property, if the silver glass beads are intended to be used as implants/medical devices, the authors need to assess their efficacy to delay or inhibit the growth of bacteria on the surface of the silver coated glass beads (no mechanical agitation needed). Infections of the medical device implants do not happen in agitated setting. More often than not, the infections start after the implantations which means the bacteria would grow simultaneously with the implant/medical devices. Assessing the antibacterial property with the released silver ions from the glass beads might not provide a real picture of the efficacy of silver beads. In the actual clinical setting, the infections associated with medical devices are often manifested with the attachment of bacterial cells on the surface, leading to subsequent biofilm formation and hence the failure of the implants/devices etc. Therefore, the author can consider to grow the silver glass beads together with the target bacteria for at least 24 hours and assess the antibacterial effect by measuring the CFU of the liquid (where the bacterial cells are still planktonic state) and the CFU of the attached bacteria on silver glass beads. The log reduction of the attached bacteria and the log reduction of the planktonic bacteria should be provided. Additionally, SEM of the control vs silver glass beads could be provided.

Response 4

We fully agree with the reviewer's comments and the proposed experimental design for testing the application of silver-coated glass beads on implants and medical devices. However, as stated in lines 69 to 72: 'The ultimate goal is to combat nosocomial infections by controlling bacterial growth at water endpoints, such as siphons.' It is anticipated that the siphons will intermittently receive water following the use of the sinks in which they are installed. "Consequently, microorganisms and silver microspheres will be in contact and exposed to periodic agitation as well. For this reason, our experimental design focuses on evaluating microbial survival under agitation, which simulates the conditions expected in the siphon environment. For all the reasons mentioned, we hope that the reviewer will find the experimental design proposed in this work appropriate.

Regarding the SEM images, we have the images of the silver coated glass beads and those of the control. If you consider it interesting, I could include in the article the SEM and optical microscope images of the control glass beads (without silver coating).

Comments 1:

What determines the choice of temperature of thermal treatment of the mixture of silver nanoparticles and glass beads, as well as the time of their washing with water?

Response 1:

Thank you for your comment. To clarify your doubts, I will provide you with more information. the research project, a procedure has been carried out to optimize both the temperature of the heat treatment and the time the glass beads are in contact with the silver suspension. The optimum conditions have been those in which the silver nanoparticles have been integrated into the glass matrix without modifying or damaging the glass microspheres, as these can soften at temperatures of around 700-800ºC. In the same way, the washing time of the silver-coated microspheres, the quantity of microspheres, the volume of water, etc., have been optimized. Only tests carried out under optimal conditions have been included in the article.

Comments 2:

Why did you choose this method of applying NPs to the surface and are there other synthesis methods? This point can be added to the Introduction

Response 2:

This coating method has certain advantages over other methods such as traditional methods of immersion, vapor deposition, plasma, sputtering, dip coating, spin coating, spray coating and roll coating. The material to be coated is a glassy material that can modify its structure and shape if subjected to high temperatures. Moreover, these are microspheres with a very smooth surface, which makes it difficult to obtain a homogeneous coating.

We agree with the comment. Therefore, in the introduction reference has been made to coating methods. Ref26, Line 82.

Comments 3:

Perhaps it was necessary to rinse of glass beads for 30 minutes or an hour after their preparation so that there would not be such a strong leaching of silver ions in the first 30 minutes, what do you think?

Response 3:

Thank you for your input. The aim of these tests was to observe and study the leaching process from the first contact of the silver glass beads with water.

Comments 4:

Figure 1 does not show EDS analysis data.

Response 4

We have revised the figure 1. The data are described in lines 223 to 232. Area 1= 1.6%, Area 2= 0.1%, area 3= 2.3% and area 5= 0.1%.  If you consider that the data is clearer if expressed as in figure 5, we could  modify the image in figure 1 by including a table.

Comments 5:

Check the spelling of the ref.6.

Response 5:

Thank you for the review. The bibliographical references related to microbiological topics in the introduction have been updated and therefore this bibliographical reference has been removed.

Comments 6:

It is surprising that, when discussing such a relevant topic as the fight against multidrug-resistant microorganisms, the authors have not cited any articles from the past five years. This issue is current and important. Therefore, I suggest adding a description of relevant literature in the Introduction.

Response 6:

Answer: We fully agree with the reviewer. The introduction did not sufficiently emphasize the global issue posed by resistant microorganisms in both clinical and community settings. For this reason, and following the reviewer's suggestions, we have included text addressing this issue, along with updated references. The new text has been included in the Introduction section, between lines 40-64.