INTRODUCTION Wide spread of antibiotic resistant bacteria among agents of surgical infections decreases effectiveness of treatment and makes it necessary to search for new methods to coping with drug-resistance (Kalan and Wright, 2011; Mainous et al., 2011). Metals with antibacterial properties, for example silver, have been used for many centuries to combat with microorganisms. Nano-sized metals have high antibacterial properties because their small sizes increase surface area-to-volume ratio (Chen and Schluesener, 2008; Chaloupka et al., 2010). Complex mechanism of action of metallic nanoparticles makes it more difficult for bacteria to develop resistance. Combined action of metallic nanoparticles with antibiotics helps to increase activity of both agents and to reduce their toxicity. Because of this, the purpose of the present work was to assess prevalence of multidrug-resistant bacteria among agents of surgical infections, and to study in vitro influence of silver nanoparticles on activity of selected antibiotics against bacteria causing surgical infections. EXPERIMENTAL METHODS Study of prevalence of multidrug-resistant bacteria The study involved 196 bacterial strains isolated from patients treated in Surgical Department of Kharkiv Multiprofile Hospital № 18 (Kharkiv, Ukraine). The majority of patients were with wound infections, cholecystites or cholangites, also were present patients with peritonites, and other infections. Identification of bacteria was performed by traditional bacteriological methods; antibiotic sensitivity was done by disk diffusion method. Biosynthesis of silver nanoparticles Silver nanoparticles were produced by challenging the cell filtrate of fungus Phoma glomerata with 1 mmol/l silver nitrate. The silver nanoparticles were characterized by UV-Visible spectrophotometer and Fourier transform infrared spectroscopy. Detection the size of nanoparticles was carried out by scanning electron microscopy. ANTIBACTERIAL ACTIVITY OF ANTIBIOTICS IN COMBINATIONS WITH SILVER NANOPARTICLES AGAINST AGENTS OF SURGICAL INFECTIONS M.K. Rai1, K.V. Kon2 1Sant Gadge Baba Amravati University, Department of Biotechnology, Amravati, 444602, Maharashtra, India, Tel.: +917212662207, Fax: +917212660949, email: mkrai123@rediffmail.com 2Kharkiv National Medical University, Department of Microbiology, Virology and Immunology, Kharkiv, Ukraine, 61022, Pr. Lenina, 4, Tel.: +380507174771, email: katerynakon@gmail.com Study of in vitro activity of combinations between silver nanoparticles and antibiotics Activity of ampicillin, gentamycin, kanamycin, streptomycin and vancomycin in combination with silver nanoparticles was studied by disk diffusion method against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. RESULTS AND DISCUSSION Etiology of surgical infections and prevalence of multidrug-resistance The most often S. aureus, E. coli, P. aeruginosa, and Klebsiella pneumoniae were isolated. Polymicrobial cultures were present in 35% of patients. 123 (62.76%) of 196 isolates were multidrug-resistant. Among agents of wound infections 85 (66.4%) of 128 strains were multidrug-resistant. Therefore, obtained results demonstrate extremely high level of antibiotic resistance among agents of surgical infections and urgent need in assessing of new methods of coping with drug-resistance. Characterization of synthesized nanoparticles Extinction spectroscopy of ultraviolet (UV) and visible (Vis) light (UV-Vis spectrum) allowed confirming the presence of noble silver nanoparticles because of the characteristic plasmon resonance, which showed absorbance peak at 440 nm. Sizes of nanoparticles were in ranges 60-80 nm as was determined by scanning electron microscopy. Antibacterial activity of combinations of silver nanoparticles with antibiotics Against S. aureus the highest increase in inhibition zone area in the presence of sub-inhibitory concentration of silver nanoparticles was determined in vancomycin and streptomycin – by 67.4% and 59.5% (Fig. 1): the inhibition zone was enlarged from 17 to 22 mm for vancomycin and from 19 to 24 mm for streptomycin. Around the disks with gentamycin the inhibiton zone in the presence of nano-silver increased by 36.1% - from 18 to 21 mm. 0 100 200 300 Gentamycin Streptomycin Kanamycin Vancomycin Ampicillin E. coli S. aureus P. aeruginosa Increase in inhibition zone area, % Figure 1. Increase in inhibition zone area around the disks with antibiotics in the presence of silver nanoparticles Around the disks with kanamycin and ampicillin the increase of inhibition zone was minimal – by 29.1% and 23.4% (from 22 to 25 mm for kanamycin and from 18 to 20 mm for ampicillin). Against E. coli the highest increase in inhibition zone area was present in vancomycin and ampicillin – by 236.1% and 177.7%, respectively. In both antibiotics inhibition zones without addition of nanoparticles were absent; while in their presence they achieved 11 and 10 mm, respectively. Activity of gentamycin increased by 63.2% (diameter of inhibition zone was enlarged from 18 to 23 mm), activity of kanamycin increased by 56.2% (from 20 to 25 mm), activity of streptomycin – by 33.1% (from 13 to 15 mm). Activity of antibiotics against P. aeruginosa in the presence of silver nanoparticles was increased to the highest extent compared with other tested bacteria. These findings represent great importance owing to high prevalence of antibiotic resistance among clinical isolates of P. aeruginosa. Activity of ampicillin and vancomycin increased by 236.1%, activity of streptomycin – by 177.7% (inhibition zones diameters were enlarged to 11 mm for ampicillin and vancomycin and to 10 mm for streptomycin, while inhibition zones for these antibiotics without nanoparticles were totally absent). Activity of gentamycin and kanamycin increased not significantly – by 29.1% and 12.8% (from 22 to 25 mm and from 16 to 17 mm, respectively). Obtained results demonstrate ability of silver nanoparticles to increase the activity of different antibiotics against both gram-positive (S. aureus) and gram-negative (E. coli and P. aeruginosa) bacteria. Effect was more noticeable against gram- negative bacteria. Enhancement of activity was more significant in antibiotics which inhibit cell wall synthesis (ampicillin and vancomycin). Increase of antibiotic activity in the presence of silver nanoparticles can be explained by influence of nanoparticles on bacterial cell membrane with its damaging which facilitates penetration of antibiotics into bacterial cell (Li et al., 2005; Fayaz et al., 2009). Gram-negartive bacterial cell contains outer membrane, and its destruction with nanoparticles explains more pronounced effect of nanoparticle- antibiotic combinations against gram-negative bacteria compared with gram-positives which lack outer membrane. Furthermore, nanoparticles may inhibit active efflux of antibiotics from bacterial cell by efflux pumps responsible for antibiotic resistance. Inhibition of efflux pumps restores activity of antibiotic which lost their application (Banoee et al., 2010). CONCLUSION Biosynthetically-produced silver nanoparticles have demonstrated promising ability in increasing activity of different antibiotics against medically-important bacteria. The most pronounced effect was in beta- lactams and glycopeptides; furthermore, effect was more noticeable against gram-negative bacteria than against gram-positives. Antibiotic-nanoparticle combinations represent a promising approach in coping with bacterial resistance and future studies should be directed to assessment of time- and concentration-dependent interactions between antibiotics and different types of nanoparticles. REFERENCES [1] Kalan L, Wright GD. Antibiotic adjuvants: multicomponent anti-infective strategies. Expert Rev. Mol. 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