The Ability of Some Inorganic Nanoparticles to Inhibit Some Staphylococcus spp.

Abstract

In the last decades, antibiotics were used to treat infections caused by some Staphylococcus species, especially Staphylococcus aureus and Staphylococcus epidermidis. The widespread use of antibiotics to treat staphylococcal infections has resulted in an increase in the resistance of bacteria to antibiotics, particularly to beta-lactam antibiotics. In recent years, researchers have been working on developing new antibiotics, despite the fact that they are complex and expensive and carry a number of risks associated with drug toxicity. Using new substances that have good potential against bacterial infection without causing bacteria to become resistant to these substances is currently being researched. More research has been carried out on the effect of silver and copper nanoparticles in neutralizing staphylococcal infection in laboratory studies. The toxic effect of nanoparticles was a concern to scientists, but despite that, the studies in vivo found that there was no toxic effect at low doses of nanoparticles on rats. The findings in this field were acceptable to entice researchers to develop these substances.

1. Introduction

Bacteria belong to prokaryotic organisms, which means they have no clear nucleus such as in eukaryotic organisms. Many bacteria exist as normal flora in or on human skin, and some bacteria are opportunistic and pathogenic to their hosts; Staphylococcal bacteria have a large number of species. The species that are mentioned more than once in scientific reports that cause infections and pathogenicity to their hosts are S. aureus and S. epidermidis [1, 2]. S. aureus is Gram-positive bacteria that causes a variety of diseases. Furthermore, S. epidermidis has been identified as a second cause of wound inflammation after S. aureus in the last two decades [1]. Chemotherapy (antibiotics) and biological therapy have been used to eliminate the pathogenicity of some bacteria for decades.

Although some of the antibiotics have good results in reducing the pathogenicity of some Staphylococcal bacteria, the problem of resistance has begun to appear, for example, methicillin-resistant S. aureus (MRSA). A new agent has been applied to solve this problem, represented by nanomaterials. Silver and copper nanoparticles showed a nice result against selected pathogen isolates that were resistant to agents of antibiotics [3, 4].

This chapter explores a brief overview of S. aureus and S. epidermidis, as well as the impact of some nanoparticles in the suppression of their pathogenicity.

2. S. aureus

S. aureus produces a purple stain when Gram stain is applied to it, for this reason, it is named Gram-positive bacteria. This species is found mainly as part of the natural microbiota on the skin, gland skin, and infrequently in the mucous membrane of birds and mammals. S. aureus becomes more pathogenic than other Staphylococcal species, such as S. epidermidis, when suitable habitat elements are provided. S. aureus, which is cited in numerous scientific studies, causes a variety of diseases [5]. The virulence factors that make this species more ferocious against its host are the source of its illnesses. The use of antibiotics to treat pathogenic bacteria has increased over the last 10 years. Therefore, S. aureus has become increasingly resistant to antibiotics, as seen by the MRSA strain.

3. S. epidermidis

Another Gram-positive bacteria species is S. epidermidis. S. epidermidis belongs to coagulase-negative Staphylococci (CoNS), which means it lacks the enzyme coagulase, compared with S. aureus, which has the enzyme coagulase [6]. The usual inhabitant can also be found in human skin and mucosal membranes. S. epidermidis is infrequently known to cause infections in normal humans, but infections of this species are becoming more common in susceptible patients, particularly long-term hospital patients or patients with implanted foreign bodies [7, 8]. S. epidermidis has the ability to attach and develop on polymer surfaces, then produce extracellular slime substances, and finally cause the pathogenesis of polymer-associated illnesses [9]. The slime substance clearly guards the imbedded Staphylococci against antibiotics. Frígols et al. [10] have found that methicillin-resistant S. epidermidis (MRSE) is a common cause of infectious keratitis caused by S. epidermidis and shows a high rate of multidrug resistance.

4. Glance of nanotechnology

Nanotechnology is a new science with a short history of knowledge. Nanotechnology applications make revolutions in many fields because nanomaterial characterizations have a huge difference compared with bulk materials [11]. Bionanotechnology is a term used to describe a subfield of nanotechnology that deals with biology. It describes any materials or processes at the nanoscale that are based on biological or biologically inspired molecules, such as nanotechnology devices used in controling and monitoring in medicine. Another example uses nanocarriers loaded with medicine that are used to introduce therapy into pathogen microbes or unusual cells that belong to tissue (cancer therapy) [12]. Nanoparticles are incredibly tiny particles with sizes between 1 and 100 nanometers. Several nanoparticles have been used to test their activity against harmful microbes. Methods to synthesize these particles are divided into three categories, which are biological, chemical, and physical. Inorganic reducing agents are used in nanoparticle syntheses, such as silver and copper nitrate. Numerous inorganic nanoparticles have been employed in numerous scientific articles [13, 14, 15]. Among these, silver and copper nanoparticles are two that will be discussed in the subsections that follow.

4.1 Silver nanoparticles

Silver nanoparticles have attracted interest in the biological field due to their special characteristics, such as size and shape that depend on magnetic, optical, and electrical properties [16]. These characteristics also make it possible to use silver nanoparticles in antimicrobial applications and other medical-related applications. Many biological, chemical, and physical methods have been employed to synthesize and stabilize silver nanoparticles [17]. The popular methods for the production of nanoparticles are chemical approaches. The method using chemical materials almost contains toxic materials. Therefore, chemical methods are considered toxic, not eco-friendly, and expensive ways to synthesize nanoparticles. For this reason, easy and simple methods are required to produce silver nanoparticles without using harmful or expansive materials. Biological or green chemistry has been used in recent years in abundance [18]. Microorganisms or plant extracts are used as reducing agents to inorganic raw materials for nanoproducts [19, 20].

4.1.1 Silver nanoparticles with anti-pathogenic properties

The problem of resistant pathogen bacteria to antibiotics and the product of another generation of antibiotics is a big challenge to scientists at present. Development of a new generation of antibiotics takes time and is expansive. It is necessary to find another medicine that has stability with activity without resistant pathogen bacteria to it. It is necessary to treat harmful bacteria. Inorganic nanoparticles are a current drug that is hoped to be effective almost immediately. Silver nanoparticles have been widely used as antibacterial agents in the medical field, food storage, textile coatings, and a variety of environmental applications. Silver nanoparticles’ antimicrobial qualities have led to their employment in a variety of disciplines including medicine, industry, animal husbandry, packaging, accessories, cosmetics, health, and military applications [21]. The interest in the activity of silver nanoparticles toward the pathogen S. aureus has increased in the last 8 years, as shown in Figure 1.

Figure 1.

Increasing publication regarding the activity of silver nanoparticles against the pathogen Staphylococcus aureus in recent years [22].

The study of the synergetic effect of silver nanoparticles with antibiotics, for example, erythromycin, amoxicillin, penicillin G, clindamycin, and vancomycin against S. aureus [23] was another hope. The technique approved its activity against pathogen bacteria in vitro (inside laboratory). Due to the perfect results of antibacterial activity of silver nanoparticles combined with some antibiotics in vitro assay, these results inspired the researchers to assay this technique in vivo tests using animal models (inside the organism’s body) [24]. Xu et al. [25] demonstrated the effect of silver nanoparticles combined with vancomycin, rifampin, and other antibiotics used in their study in vitro as well as in vivo assay. The silver nanoparticles successfully passed assays in vitro and in vivo and hope to be used for human treatment in the next few years.

Resistance to silver nanoparticles by bacterial cells has been reported. Elbehiry et al. [26] explored the resistance development of S. aureus to silver nanoparticles after multiple generations of S. aureus. As well, Panáek et al. [27] demonstrated that after repeated exposure to inhibitor concentrations of silver nanoparticles, Gram-negative bacteria such as Escherichia coli develop resistance to silver nanoparticles. This resistance is not concerning due to these phenotypic changes and not genetic changes, which means this factor will not be transported to future generations of bacteria cells. Furthermore, the multiple mechanisms of action of nanoparticles may limit the development of bacterial resistance to nanoparticles.

4.2 Copper nanoparticles

Finding another nanoparticle with excellent properties at a lower cost is becoming more required nowadays. Copper nanoparticles have been widely used as inexpensive and effective therapeutic for certain harmful bacteria. Therefore, copper nanoparticles could be a useful antibacterial agent in the coming days. Copper nanoparticles are highly reactive due to their high surface-to-volume ratio; this allows them to easily interact with other particles and boost their antibacterial efficiency. Copper nanoparticles have received much interest because of their unique physiochemical properties, surface-to-volume ratio, cheap preparation, and nontoxic preparation. They have many amazing uses in various domains, such as anticancer activity [28], antimicrobial activity [29], antifungal activity [30], catalysts [31], and antioxidant activity [32]. The creation of copper nanoparticles has been described in numerous scientific works using chemical, physical, and biological methods [33]. The biological method uses natural reducing agents that can be found in plant extracts, fungi, and bacteria to convert copper salt into copper nanoparticles [34, 35, 36]. A commendable job has been done regarding the production and stability of copper nanoparticles by using biological processes.

4.2.1 Copper nanoparticles as antibiotics for some human pathogen bacteria

Copper metal is one of the essential elements, especially in most living organisms. The particles of copper in the nanoscale have different properties compared with copper particles and have many applications, one of them is an antibacterial agent. Copper nanoparticles possess better properties as inorganic antibacterial agents relative to other expansive metal nanoparticles such as gold and silver [37]. For instance, the copper nanoparticles recorded higher antibacterial activity relative to silver nanoparticles against some human pathogen bacteria [38].

According to Figure 2, copper nanoparticles have received a lot of attention from researchers lately due to their antibacterial action against many pathogens of S. aureus [40].

Figure 2.

Increasing publication regarding the activity of copper nanoparticles against the pathogen Staphylococcus aureus in recent years [39].

Despite only a few scientific studies examining the efficacy of copper nanoparticles against Staphylococcus epidermidis [41, 42], they have revealed potency against this isolate. Consequently, it is a promising medical treatment.

Another strategy has been applied using a solution of antibiotics with copper nanoparticles. Selvarani [43] showed the effect of tetracycline alone against S. aureus, recording an inhibition zone at 25.3 mm using the disc diffusion method, but when impregnating the disc of antibiotics with 50 μl of freshly prepared copper nanoparticles, the diameter of the zone of inhibition was increased to 32.6 mm, increasing by 28%. The same study with another antibiotic (Rifampicin) recorded an increase of 13.8% compared with Rifampicin alone. Additionally, Woźniak-Budych et al. [44] investigated the activity of Rifampicin combined with copper nanoparticles toward four bacterial strains, one of those being S. aureus, and found a synergic effect of Rifampicin with nanoparticles was a successful way to prevent the development of resistance. Therefore, there is hope through combining inactive antibiotics with some inorganic copper nanoparticles to convert them into active antibiotics. It is another promising solution to the problem of S. aureus and S. epidermidis antibiotic resistance.

4.3 Mechanism of antibacterial activity of silver and copper nanoparticles toward bacteria

The antibiotics are categorized according to their specific targets, which makes them safe for human use. Antibiotics’ mechanisms of action include five basic mechanisms against bacterial cells, which are inhibition of cell wall synthesis, inhibition of protein synthesis (translation), alteration of cell membranes, inhibition of nucleic acid synthesis, and finally antimetabolite activity [45]. Silver nanoparticles no longer have a clear mechanism, such as antibiotics against pathogenic bacteria, but many studies have been conducted on their possible mechanisms of antibacterial properties [46, 47, 48]. In recent years, silver nanoparticles have been used in many fields, including medicine, air and water purification, and others [49].

The properties of the mechanisms for silver nanoparticles are well described [48]. The nanoparticles of silver that adhere to the surface of the bacterial cell membrane probably disrupt the functions of the cell membrane, such as respiration and substance transport, as well as cell membrane separation from the cell wall partial or complete [50]. The increased stickiness of nanoparticles results in increased destruction permeability capacity and cell division that lead to a fast rate of death for bacteria compared with the low concertation of nanoparticles. The above description includes the hypothesis of silver nanoparticles’ mechanism of antibacterial that sticks to cell walls and cell membranes. The silver nanoparticles can pass through the cell wall of bacteria and reach the cell membrane easily because there are pores in the cell wall. However, there is another hypothesis about silver nanoparticles that successfully reach inside bacterial cells. As a result, silver nanoparticles’ creation links with phosphorus and sulfur present in cytoplasmic molecules of bacteria, such as DNA, causing the death and destruction of bacteria [51]. Another possible effect of silver nanoparticles is the disruption product of energy compounds (adenosine triphosphate ATP) and the generation of DNA. They then produce reactive oxygen species (ROS), which are considered toxic to bacterial cells [52].

The mode of action of copper nanoparticles toward antibacterial has little information explained. The researcher proposed the mechanism of activity of copper nanoparticles on pathogen bacteria may have a similar mode of action to silver nanoparticles [53]. Schrand et al. [54], it was hypothesized that copper nanoparticles work as antibacterial agents against many bacteria species due to interaction with SH-groups that result in protein denaturation. Copper nanoparticles may have an effect on cell membrane because of their affinity toward the amines and carboxyl groups that are found on the membranes of some bacteria strains [55]. The nanoparticles can enter a cell through the pores in the cell membrane because of their nanoscale size, or get inside bacteria through ion channels and transport proteins in the membrane of bacteria. After copper nanoparticles enter the cell, they may bind to DNA molecules and disturb the structure of the DNA strands, as well as find copper ions inside bacterial cells, which also disturb biochemical processes [56]. Deryabin et al. [57] hypothesized another mechanism, copper nanoparticles may accumulate on the cell of bacteria and diffuse inside the cell, causing oxidative stress that causes the cell of bacteria to die. Figure 3 depicts all possible mechanisms of action for silver and copper nanoparticles. Due to limited studies discussing the mechanisms of bioactivities of copper nanoparticles against bacteria, the mechanism of action of copper nanoparticles needs more studies about their cytotoxicity and safety to be used as a human medicine agent to treat harmful bacteria.

Figure 3.

Nanoparticles’ possible mechanism of action on and in bacterial cells.

4.4 The possible toxic effects of silver and copper nanoparticles

The toxic effects of nanoparticles of silver and copper have been studied. In the study by Nakkala et al. [58], the rats were treated orally with 5 and 10 mg/kg of silver nanoparticles for 28 days. The rat organs, such as liver, lungs, kidney, spleen, heart, testes, and brain, showed no histopathological changes at the end of the test. Elbehiry et al. [26] also studied the toxic effects of silver nanoparticles at 0.25, 0.5, and 1 mg/kg in the brain, liver, kidneys, heart, and spleen of rats. After 28 days of testing, they did not find any histological changes in the organs of experimental animals. In contrast with the findings of Kim et al. [59], they noted that after feeding the rat with silver nanoparticles for long-term oral administrated concentrations of 30, 300, and 1000 mg/kg, any changes in the weight of the rat body were not recorded, but they noted the accumulated silver nanoparticles in different tissue organs. In addition, Tiwari et al. [60] found that the treated cells of the liver and kidney with high doses of silver nanoparticles at 20 and 40 mg/kg showed abnormal structures of the cell, as well as nanoparticle deposition in the cytoplasm and nuclear membrane of tested orangs at 40 mg/kg concentration.

Doudi and Setorki [61] treated the experimental rats with different concentrations of copper nanoparticles (10, 100, and 300 mg/kg) after they studied the effects on the liver and lungs. The results of their work have been shown to cause structural changes in cells of the liver and lungs at high doses. Another work by Lei et al. [62] took tissue sections from the liver and kidney of rats that were treated with 100 and 200 mg/kg of copper nanoparticles once a day for 5 days. The necrosis in the liver has been noted at 200 mg/kg with structural changes in the kidney, while there was no alteration in the structure of the liver and kidney cells at 100 mg/kg. Wang et al. [63] studied the effects of various concentrations of copper nanoparticles on rats. Their study explored histological alterations in the liver, spleen, and kidney in male and female rats at 1250 and 2500 mg/kg.

The previous studies of the effects of silver and copper nanoparticles on the organs of rats at various doses of nanoparticles above concluded that the high doses showed clear accumulation and toxic effects of nanoparticles in vivo studies. While at low doses, there were no histological changes in the rats with safe use. Future work is required to clarify the biological effects of silver and copper nanoparticles using animal models.

5. Conclusions

The pathogenicity of Staphylococcal, especially Staphylococcus aureus, is widespread in nosocomial infections and long hospitality treatment periods between patients. However, Staphylococcus epidermidis has a recent history of pathogenicity with inflammation wounds. The drugs used in the protocol of treatment for bacterial infection are antibiotics. Widespread use of antibiotics produces problems for medical scientists related to resistant bacteria to these drugs. These problems come from transport genes responsible for resistance from honor plasmid to receiving plasmid in bacteria.

The development of a new generation of antibiotics takes time and is expansive at the same time. Using a new drug with excellent bactericide activity is a recent option to solve this problem in the medicine sector. Nanoscience is one of the options selected to solve this challenge. A number of inorganic nanoparticles have been synthesized using biological methods. Silver nanoparticles have been approved for their activity against many pathogens, including S. aureus and S. epidermidis, depending on several scientific reviews without resistance bacteria to it. The other inorganic nanoparticles, such as copper nanoparticles, have been reviewed, and the activity of copper nanoparticles toward several human pathogens of S. aureus and a limited number of S. epidermidis has been reviewed.

Antibiotics have a known mechanism of activity against bacteria. In comparison with silver and copper nanoparticles, they have antibacterial activity but no clear mechanism, such as in antibiotics. Four suggested hypotheses about the mechanism of inorganic silver and copper nanoparticles have been discussed. The nanoparticles first adhere and accumulate on the cell walls of bacteria. The second hypothesis suggested transporting the nanoparticles of silver and copper passed through the pore in the cell wall and reached the surface of the cell membrane. Some of the nanoparticles that accumulated on the surface of the cell membrane worked to modify the permeability of the cell membrane and disturb the respiration process in the cell membrane of bacteria, resulting in the entry of harmful materials inside the cell, causing death to bacteria. The nanoparticles that successfully passed the cell membrane using channel of ion exchange or proteins channel or even through the self-membrane of cell because they have tiny small size compared with the size of the membrane reacted with the DNA molecules causing an inhibition of the DNA replication, and because of that, there is no transcription and translation happened. The last hypothesis talked about the creation of reactive oxygen radicals. This product is considered toxic to cells. More investigated studies in vivo as animal models need to study the safety of the nanoparticles to use them as drugs.

Conflict of interest

The authors declare no conflict of interest.