Green Synthesis of Silver Nanoparticles: An Application of Antibiotics Mohammed A. Abd Ali 1* , Ali Aboud Shareef 2 1 Department of Biology, College of Science, University of Misan, Misan 62001, Iraq 2 Department of Biology, College of Education for Pure Sciences, University of Basra, Basra 61004, Iraq Corresponding Author Email: waleedabas22@uomisan.edu.iq https://doi.org/10.18280/rcma.320104 ABSTRACT Received: 6 January 2022 Accepted: 15 February 2022 The goal of this research is to use dental caries patients’ oral cavity-isolated Enterobacter aerogenes bacterial strains (S1, S2 and S3) to create silver nanoparticles (AgNPs) in an environmentally friendly and cost-effective manner. In addition, the study explores the combination of antibiotics with Streptococcus mitis MDR, which was isolated from patients with dental caries to determine their antibacterial efficiency. Clinical bacterial strains identified from dental caries patients' mouths were all resistant to standard antibiotics. Antibiotics and AgNPs have a synergistic impact, which suggests that antibiotics will make up a larger portion of the diet. It was shown that erythromycin E had the greatest synergistic impact with AgNPs (0.1 mg/ml), but Streptomycin and Tetracycline had only 6 mm inhibitory zones when paired with AgNPs (0.1 mg/ml) in comparison. Antagonizing effects are meant by this. It was revealed that antibiotics such as penicillin P and cephalexin CN had distinct effects on patients. When used in combination with antibiotics, Enterobacter aerogenes AgNPs demonstrated excellent antibacterial efficacy on Streptococcus mitis isolates. As a result, AgNPs in the dental care area have a wide range of applications. Keywords: green synthesis, silver nanoparticles, dental, XRD, antagonistic effects 1. INTRODUCTION Humans have been searching for new antibiotics since the discovery of penicillin at the turn of the twentieth century, despite the fact that bacteria are developing resistance mechanisms to the antibiotics already in use [1]. In addition to increasing the likelihood of accidents, the rise in antibiotic resistance to conventional antibiotics is an important worldwide health issue [2]. Unique structural size and shape, which are defined by their chemical, biological, and physical properties, nanotechnology has emerged as a rapidly expanding area of nanoscience with crucial applications, including the creation of nanomaterials and their application in medicine and biology [3]. It is common to refer to nanotechnology as the "fourth industrial revolution" in the history of humanity civilization. According to Parthasarathi and Thilagavathi [4], ceramics, metals, polymers, and biomaterials are all included in this category. Antibiotics, sunscreens, and sunblocks are examples of biogenic products that are being developed and improved., it has made a substantial contribution [5]. Since environmentally friendly derivates are used to reduce nanoparticle metals, rather than hazardous chemicals, the green synthesis method is superior to the traditional chemical method [6]. According to numerous studies, nanoparticle products have evolved over time. These nanoparticles have already been used in implant coatings as well as food containers and ointments. The United States of America's Food and Medicine Administration has given clearance to use the drug [7]. According to numerous studies, Nano silver is bactericidal to both gram-positive and gram-negative microorganisms [8]. Microorganisms that live in the mouth cavity form a self- contained ecosystem [9]. Despite its prevalence, dental caries is one of the world's most common chronic infectious diseases. If the enamel is damaged, caries can begin as small areas of demineralization beneath the surface of the tooth's surface and progress through the dentine and into the pulp [10]. An infection caused by bacteria weakens the teeth's enamel, dentin, and cementum and can cause tooth loss. In most developed nations, dental caries affects 60–90% of school- aged children and the vast majority of adults, making it a serious public health issue [11]. Traditional medical infections often include a single infectious agent, and that infectious agent may also be present in isolated animals that are not traditionally hosts [12]. On the other hand, dental caries can be brought on by oral commensal microbes that spread a polymicrobial infection. About 600 different species of microorganisms have been found in the oral microbiome, which is a microbiome that lives inside the human mouth [13]. Cells, water, and bacteria extracellularly form a biofilm, which adheres to the surface of an organism [14]. The formation of biofilms is a result of a variety of environmental factors [15]. As the plankton moves from free-swimming to sessile life in a biofilm, a range of environmental and genetic factors must be taken into account that are specific to the individual species [16]. Periodontal disease is defined as the breakdown of periodontal teeth's supporting tissues in the oral cavity, such as alveolar bone and gingiva, which can be a risk factor for certain systemic conditions [17]. Topcuoglu et al. [18] discovered in a study that red-complex bacteria were the most Revue des Composites et des Matériaux Avancés-Journal of Composite and Advanced Materials Vol. 32, No. 1, February, 2022, pp. 25-31 Journal homepage: http://iieta.org/journals/rcma 25