Vibrio vulnificus, a ubiquitous microorganism in aquatic environments, causes serious septicemia to the immunocompromised host. In addition to protoheme, this species can utilize Fe-TCPP [ferric tetrakis (4-carboxyphenyl) porphine] as an iron source. In the present study, heme c bound covalently to the protein in cytochrome c, as well as the Fe-TCPP complex formed with a nanopeptide with a high affinity, was found to be useful iron sources for V. vulnificus. This bacterium was also revealed to use Zn-TCPP as a single zinc source. However, other metalloporphyrins such as Mn-TCPP and Pt-TCPP delayed the bacterial growth in the broth containing Fe-TCPP, suggesting interference in the iron assimilation. These results indicate that V. vulnificus may acquire metal ions from both free and peptide-bound metalloporphyrins.

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The bactericidal effect of HM-242, a novel antimicrobial agent, against Pseudomonas aeruginosa was investigated by using Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values and the time-kill study. Furthermore, we also morphologically investigated its effect against P. aeruginosa by use of transmission electron microscopy (TEM) in comparison with that of chlorhexidine digluconate (CHG). The bactericidal activity of HM-242 after 1 min incubation evaluated by MBC was 25 μg/mL, while the MBC of CHG was 50 μg/mL. In the time-kill study, the killing activity of HM-242 with 25 μg/mL incubation was stronger than that of CHG with 50 μg/mL incubation. MIC values of HM-242 and CHG against P. aeruginosa were 25 μg/mL and 12.5 μg/mL, respectively. We also observed via TEM the morphological changes in the test bacteria after being treated with each drug at 1/2MBC, 1MBC, 2MBC and 4MBC after 1 min or 5 min incubation. Under treatment with the same concentration of the test drugs, the cell damage with HM-242 treatment was greater than that with CHG. The appearance of empty cells was recognized at the concentrations greater than 50 μg/mL (2MBC) of HM-242 and 200 μg/mL of CHG (4MBC) after 1 min exposure, although no cell damage was evident below these concentrations. The cell-damaging effect against the test strain was dependent on the drug concentration and incubation time. The release of cell components and bleb formation were also recognized. These results suggest that HM-242 has more potent bactericidal activity in low concentrations under shorter time treatments than CHG. Both HM-242 and CHG act on the cell membrane and cell wall of P. aeruginosa and can destroy the cell integrity. We finally emphasize that HM-242 as well as CHG might be a suitable disinfectant for use in the medical field.

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Several studies have been performed to assess the effectivesness of the antibacterial coating of a biomaterial to reduce surgical site infection. However, evaluations of these materials are inconsistent, and therefore it is difficult to compare their antibacterial performance. In this study, we evaluated the influence of different media such as nutrient broth (NB), Mueller-Hinton broth (MHB) and fetal bovine serum (FBS) on the antibacterial activity of AgNO₃- or gentamicin-added bone cement using a modified ISO 22196 standard to devise a method to evaluate the antibacterial activity of biomaterials in vitro. The antibacterial activity results against Staphylococcus aureus and Escherichia coli were different in each medium. The antibacterial activity of AgNO₃ in FBS was lower than the other media, whereas the antibacterial activity of gentamicin in FBS was higher than in the other media. It was assumed that the fluctuating antibacterial activity was influenced by serum components. The results showed that the ISO 22196 antibacterial evaluation method is suitable to evaluate antibacterial biomaterials after modifying the medium to FBS.

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Heterotrophic bacteria constituting the biofilm produced in a kitchen sink drain were analyzed, and the biofilm formation abilities and the hydrophobicity of the cell surface layer were measured for the isolates. When the biofilm sample was cultured at 36°C and 25°C for 7 days, there were about 10 times more colonies on oligotrophic R2A agar medium than on eutrophic BHI agar medium. From isolates from the biofilm sample, 13 bacterial species were detected. To examine the biofilm formation ability of these strains, we measured the absorbance (OD₅₇₀) by crystal violet staining. The absorbance of Brevibacterium casei 7-R-36-1 was the highest (3.029). In the comparison of the absorbance values between genera, Brevibacterium spp. (4 strains) showed the highest absorbance (mean: 2.056), followed by K. pneumoniae (4 strains) with a mean of 1.111. Regarding the hydrophobicity of the isolates, the values ranged from 0.002 for P. nitroreducens (strain 1-B-36-2) to 0.096 for M. lacticum (strain 5-R-25-2). The hydrophobicity values were generally low, and the cell surface layer of all tested strains was highly hydrophilic. The diversity of species of bacteria in the biofilm sample produced in the kitchen sink drain was recognized, and all the isolates had biofilm formation abilities.

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The thermal death of the spores of Bacillus subtilis 168 in oil-water systems including emulsions and separated layers consisting of phosphate buffer and soybean oil or n-hexadecane was investigated. The resultant survivor curve consisted of two phases, an initial rapid reduction followed by a slow reduction, possibly as reflected by the death in the water phase and the oil phase, respectively. The concentration of oil in the system strikingly affected the pattern of thermal death. These results suggest that the spore location in the oil-water system may be a critical factor in determining the heat resistance.

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In this study we evaluated the ability of the UV-A-LED to eliminate bacteria in a colored beverage. Ten edible pigments were used to make a colored solution at concentrations of 1.0%, 0.1%, 0.01% and 0.001%. We used a colony-forming assay to monitor the bactericidal action against the bacteria. The bactericidal effect of UV-A-LED against Escherichia coli DH5α decreased with the increasing concentration of almost all of the edible pigments. Although less effective in colored solutions and commercially available orange juice than in the positive control PBS, it holds potential for further development and use to ensure food and water safety.

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