Antimicrobial resistance presents major global concerns to patient health. In this study, metal ions of molybdenum, rhenium, yttrium and thallium were tested against bacteria in planktonic and biofilm form using one strain of Klebsiella pneumoniae and Acinetobacter baumannii. The antimicrobial efficacy of the metal ions was evaluated against the planktonic bacterial strains using minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations, whilst the efficacy of the metal ions against biofilms was tested using a crystal violet biofilm assay. Live Dead staining was used to visualize the antimicrobial activity elicited by the metal ions on the bacterial cell. The results showed that higher concentrations of the metals were required to inhibit the growth of biofilms (72·9 mg l−1 to 416·7 mg l−1), in comparison to their planktonic counterparts. MICs of the metal ions (<46·9 mg l−1) (planktonic cells) did not affect biofilm formation. Overall, rhenium and yttrium were effective antimicrobial agents. Molybdenum demonstrated the greatest level of biotoxicity. When taking into account these results and the known toxicity of thallium, it is possible that rhenium or yttrium ions could be developed as effective biocidal formulations in order to prevent transmission in healthcare environments. Significance and Impact of the Study The metal ions, molybdenum, rhenium, thallium and yttrium were tested against both Klebsiella pneumoniae and Acinetobacter baumannii in planktonic and biofilm forms. This research demonstrated that all the metal ions may be effective antimicrobial agents. However, molybdenum induced high levels of cytotoxicity, whilst, there was no significant difference in the toxicity of the other metal ions tested. When considering the results for the antimicrobial efficacy and biotoxicity of the metal ions, in conjunction with the known toxicity of thallium in certain chemical compositions, it was concluded that overall rhenium or yttrium ions may be effective antimicrobial agents, one potential application may be utilizing these metal ions in hospital surface cleaning formulations.
Food preparation areas in commercial bakeries present surfaces for continual organic fouling. The detection of retained food components and microorganisms on stainless steel surfaces situated for one month in the weighing in area, pastry and confectionary production areas of a bakery were investigated using different methods. Scanning electron microscopy demonstrated the morphology of the material on the surfaces from all three areas, with the weighing in area demonstrating a more even coverage of material. Differential staining assays demonstrated a high percentage coverage of organic material heterogeneously distributed across the surfaces. Differential staining also demonstrated that the amount of organic material on the surface from the confectionary area was significantly greater than from both the pastry and weighing in areas. Although, UV at 353 nm did not detect residual surface fouling, performance of the UV detection was optimised and demonstrated that the residual organic material on the weighing in area and the pastry samples was best illuminated at 510-560 nm, and from the confectionary area of the bakery at 590-650 nm. ATP bioluminescence revealed the confectionary production area contained the highest level of biofouling. Contact plates determined that only low microbial counts (≤ 2) CFU/cm 2) were recovered from the surfaces. Changes in the physicochemistry (increased hydrophobicity) demonstrated that all the surfaces were fouled (ΔGiwi-26.8 mJ/m 2 to-45.4 mJ/m 2). Fourier Transform Infra-Red Spectroscopy (FTIR) demonstrated that all the surfaces had retained fats,
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