Abstract
Antibiotic resistance in pathogenic bacteria is emerging as an issue of serious concern in bio-medical research as well as food and health organizations. Metal complexes are currently being employed in medical devices for their inhibition to bacterial adherence and antibacterial activities. The primary aim of this study was to evaluate the antibacterial activities of pure metals, including selenium, germanium and lithium on planktonic cultures and biofilms of three bacterial species: S. aureus SH1000, P aeruginosa PA01 and E. coli. O157:H7. The antagonistic effects of selenium, germanium and lithium on these three bacterial species were examined using zone of inhibition assay. The minimum inhibitory concentrations and minimum bactericidal concentrations of antibiotics (rifampicin, mupirocin and ciprofloxacin) and metals (selenium, germanium and lithium) were measured. The minimum biofilm eradication concentrations (MBEC) of metals were determined against biofilms composed of S. aureus SH1000 and P. aeruginosa PA01. Metal susceptibility tests suggested that biofilms displayed increased resistance over their planktonic state. Differential inhibitory effects were observed for different strains of planktonic and biofilm bacteria in response to different metals and their varying concentrations. Amongst the three metals tested, selenium proved to be the most active against all three species, whereas lithium demonstrated the least inhibitory effects. Scanning electron microscope (SEM) image analysis revealed several detrimental structural changes in bacterial cells exposed to metals compared to those grown in the metal-free culture. In conclusion, the results demonstrate the antibacterial efficacy of pure metals against planktonic and biofilm bacteria paving the way for further similar investigations in search of alternative antibacterial agents. Key words: Antibiotic resistance, antibacterial, metal, biofilm, planktonic.
Highlights
Antibiotic resistance in pathogenic bacteria is emerging as a global issue of serious concern in bio-medical research as well as food and health organizations
Bacteria in biofilms are less susceptible to antibiotics leading to various infections and diseases (Kolenbrander, 2000) than their planktonic counterparts since antibiotic resistance in biofilms appears to depend on multicellular strategies (Hoyle and Costerton, 1991; Lewis, 2005; Stewart and William, 2001; Walters et al, 2003)
The antagonistic effects of selenium, germanium and lithium were tested against the three bacterial species using the well diffusion assay
Summary
Antibiotic resistance in pathogenic bacteria is emerging as a global issue of serious concern in bio-medical research as well as food and health organizations. Pathogenicity of microorganisms is often enhanced when growing as a biofilm, which can develop into a multi-strain, dense-layered bacterial community protected by several levels of polymeric compounds, exhibiting increased resistance against external factors and antimicrobial agents (Chambless et al, 2006; Costerton et al, 1999; Jefferson et al, 2005). The problem demands efforts to search for other antibacterial agents to fight against complex antibiotic resistant infections. Owing to their significant roles in science, metals have been drawing continual interest as antibacterial agents. A baseline data on the antibacterial efficacies of different metals is essential to develop superior antibacterial agents
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