Synergistic reaction of silver nitrate, silver nanoparticles, and methylene blue against bacteria

Abstract

In this paper we describe the antibacterial effect of methylene blue, MB, and silver nitrate reacting alone and in combination against five bacterial strains including Serratia marcescens and Escherichia coli bacteria. The data presented suggest that when the two components are combined and react together against bacteria, the effects can be up to three orders of magnitude greater than that of the sum of the two components reacting alone against bacteria. Analysis of the experimental data provides proof that a synergistic mechanism is operative within a dose range when the two components react together, and additive when reacting alone against bacteria.bacteria | synergistic effect | methylene blue | silver ions B acterial infections cause countless deaths in humans and animals. The increasing resistance and immunity of many bacteria to antibiotics demands that an effective means for the inactivation of bacteria becomes available that can overcome or negate the mechanism that bacteria use to inactivate the reactive agents before they render their lethal action on those organisms. The two antibacterial agents that we used in this study were methylene blue (MB) and silver nitrate. Each of these alone is known to be an effective antibacterial agent. The data presented in this study show that they make a synergistic agent pair against the five bacteria studied. MB is used as a bacterial inactivator for skin treatment, dental therapy, and other areas in need of bacterial disinfection (1-3). MB is a cation, whereas in its reduced leuco form MB has a pK a of 5.8 and low ionization at neutral physiological pH. This enables bacteria to reduce and inactivate MB to the leuco form. In fact, the discoloration of MB has been an indication of the presence of bacteria. In its cationic form, MB irradiated with 630-680-nm light is used for cancer therapy and as an effective bactericidal and activating agent. MB is an effective antibacterial agent owing to its ability to generate a high concentration of singlet oxygen, 1 O 2 ( 1 Δ g ), and other reactive oxygen species, such as OH • radicals (ROS), when irradiated with red light, which in contrast to UV light does not harm humans or animals cells. Therefore, the MB bacterial inactivation process is very safe and effective owing to the high reactivity of ROS with bacterial outer-cell membrane. It is found that the photogenerated singlet oxygen reacts against tryptophan and other outer-membrane molecules, resulting in damage to the bacterial cell and inhibiting protein production. ROS may also create a hole in the bacterial cell wall, which allows MB radicals to penetrate through the bacterial membrane and attack DNA, forming dimers which prevent it from replicating and consequently induce bacterial inactivation. The photoreaction that generates singlet oxygen and OH • radicals proceeds as follows: i) MB in water solution is excited to the first singlet state MB*:MB + hν (660 nm) →MB*; ii) MB* decays to the triplet state 3 MB* with a lifetime of ∼10 −9 s: MB* → 3 MB*; iii) The tripl...

Detection and Inhibition of Bacteria on a Dual‐Functional Silver Platform

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“…In parallel to detection, inhibition of bacteria is not only required in clinics, but is also a daily issue for health care . Notably, efficient inhibition of bacteria relies on engineered materials and should address the following aspects: 1) designed materials structures for bacteria surface adhesion and long‐term antibacterial effects; 2) selection and loading of antibacterial reagents to form hybrids; 3) inherent toxicological effects of nanomaterials toward the hosts; and 4) new perspectives toward the biological mechanism during antibacterial process . Most current efforts are focused on some of the above issues and few reports are on the design of one platform to tackle these aspects in all.…”

“…For biotoxicity, antibacterial effects by noble metals such as silver are widely applied in hospitals and daily life. [9a,17] Notably, new inhibition mechanisms of bacteria by noble metals remain to be explored for high antibacterial capability, which can be decided by the tailored material structures. Furthermore, development of a dual‐functional material is challenging and in demand, engaging advanced applications for both bioanalysis and biotoxicity.…”

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Silver‐Infused Porphyrinic Metal–Organic Framework: Surface‐Adaptive, On‐Demand Nanoplatform for Synergistic Bacteria Killing and Wound Disinfection

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