Antibacterial potential of silver nanoparticles against isolated urinary tract infectious bacterial pathogens

Patients with non-infectious disease who have stay in hospital have high risk to acquire nosocomial infection. It has been reported that, 10% hospital patients acquire this infection while staying in hospital (Asefzadeh 2005). Martinez and Baquero (2002) have reported from their research that, nosocomial infectious bacteria exhibited least susceptibility to antibiotics and some of these bacteria out rightly developed multidrug resistance to these antibiotics. Recently from a 3-year follow-up study in USA, Dowzicky and Park (2008) reported that, UTI bacterial pathogens have exhibited decreased susceptibility rates to tigecycline over the years. Antibacterial property of silver nanoparticles would be the alternative to overcome the resistance problem.

In our present study, E. coli (47%) was found predominant and a similar result was reported by Ravikumar et al. (2010). Despite the availability of antibiotics, UTIs remain the most common bacterial infections in human populations (Phillippon et al. 1989). Urinary tract infections occur more frequently in females (63%) than in males (Schaeffer et al. 2001). Silver is known for its antimicrobial properties and has been used for years in the medical field for antimicrobial applications and even has shown to prevent HIV binding to host cells (Nino-Martinez et al. 2008; Alt et al. 2004; Lee et al. 2007). Additionally, silver has been used in water and air filtration to eliminate microorganisms (Chou et al. 2005).

Previous reports stated that, the silver nanoparticles have potential antibacterial property against E. coli, S. aureus, Staphylococcus epidermis, Leuconostoc mesenteroides, Bacillus subtilis, Klebsiella mobilis and K. pneumonia (Benn and Westerhoff 2008; Chen and Chiang 2008; Falletta et al. 2008; Hernandez-Sierra et al. 2008; Ingle et al. 2008; Jung et al. 2009; Kim 2007; Kim et al. 2007, 2009; Kvitek et al. 2008; Raffi et al. 2008; Ruparelia et al. 2008; Smetana et al. 2008; Sondi and Salopek-Sondi 2004; Vertelov et al. 2008; Yang et al. 2009; Yoon et al. 2008a, b). It has been shown that silver nanoparticles prepared with a variety of synthetic methods have effective antimicrobial activity (Lok et al. 2006; Baker et al. 2005; Aymonier et al. 2002; Melaiye et al. 2005; Sondi and Salopek-Sondi 2004; Kim et al. 2008; Lee et al. 2008; Alt et al. 2004). In the present study, the silver nanoparticles were prepared by chemical reduction method to assess the antibacterial activity. The results of the UV–VIS absorption showed increasing colour intensity with increased time intervals and this might be due to the production of the silver nanoparticles and the formation of the brownish yellow colour might be due to the excitation of the surface plasmon vibration of the synthesized silver nanoparticles (Krishnaraj et al. 2010). The result of the XRD pattern indicates the presence of sharp bands of Bragg peaks and this might be due to the stabilizing of the synthesized nanoparticles by chemical reducing agents and thus confirming the crystallization of the bioorganic phase occurs on the surface of the silver nanoparticles (Sathishkumar et al. 2009).

Pseudomonas aeruginosa showed maximum sensitivity (11 ± 0.58 mm) at 20 μg disc−1 followed by Enterobacter sp. (8 ± 0.49 mm). The predominant isolate E. coli showed no sensitivity, it might be due to the multidrug resistance nature of E. coli developed by point mutations. The mechanism of action may be due to the silver and silver nanoparticles attach to the surface of the cell membrane and disturbing permeability and respiration functions of the cell, moreover, due to the uptake of free silver ions followed by disruption of ATP production and DNA replication. Smaller silver and silver nanoparticles having the large surface area available for interaction would give more bactericidal effect than the larger silver and silver nanoparticles (Kvitek et al. 2008). Normally silver nanoparticles interactions with bacteria are dependent on the size and shape of the nanoparticles (Panacek et al. 2006; Morones et al. 2005; Pal et al. 2007). It is concluded from the present study that, the silver nanoparticles could be used as an effective antibacterial agent for the management of urinary tract infections caused by P. aeruginosa and Enterobacter sp. after successful completion of in vivo studies and clinical trials.