Pseudomonas aeruginosa to benzalkonium chloride (BC) were studied. The effluence of cell components was observed in susceptible P. aeruginosa by electron microscopy, but resistant P. aeruginosa seemed to be undamaged. No marked changes in cell surface potential between Escherichia coli NIHJC-2 and a spheroplast strain were found. The contents of phospholipids (PL) and fatty and neutral lipids (FNL) in the cell walls of resistant P. aeruginosa were higher than those in the cell walls of susceptible P. aeruginosa. The amounts of BC adsorbed to PL and FNL of cell walls of BC-resistant P. aeruginosa were lower than those for BC-susceptible P. aeruginosa. Fifteen species of cellular fatty acids were identified by capillary gas chromatography and gas chromatography-mass spectrometry. The ability of BC to permeate the cell wall was reduced because of the increase in cellular fatty acids. These results suggested that the resistance of P. aeruginosa to BC is mainly a result of increases in the contents of PL and FNL. In resistant P. aeruginosa, the decrease in the amount of BC adsorbed is likely to be the result of increases in the contents of PL and FNL. There are many reports on the mechanisms of bacterial resistance to antibiotics (5
Anti‐MRSA activity of sophoraflavanone G (SFG) and synergism between SFG and antibacterial agents against MRSA (methicillin‐resistant Staphylococcus aureus) were evaluated by means of Minimal Inhibitory Concentrations (MIC). The MICs of SFG against 27 strains of MRSA ranged from 3·13 to 6·25 μg ml−1. Synergism between SFG and vancomycin hydrochloride (VCM) or fosfomycin (FOM) was observed (the fraction inhibitory concentration (FIC) indices were 0·16 and 0·48), while partial synergism was admitted between SFG and other antibacterial agents such as methicillin (DMPPC), cefzonam (CZON), gentamicin (GM), minocycline (MINO) and levofloxacin (LVFX) (the FIC indices were 0·71, 0·73, 0·69, 0·65 and 0·58, respectively). These findings suggest that SFG in combination with VCM or FOM may be useful in controlling MRSA infections.
The bactericidal activity of OPB-2045 (1-(3,4-dichlorobenzyl)-5-octylbiguanide monohydrochloride hemihydrate) at several concentrations against Pseudomonas aeruginosa IFO 13275 was investigated morphologically by transmission and scanning electron microscopy. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of OPB-2045 against P. aeruginosa were the same, at 12.5 microg mL(-1), suggesting that it may be a suitable disinfectant for use in the medical field. Test bacteria were treated at concentrations of one half the MIC value (6.25 microg mL(-1)), the MIC value (12.5 microg mL(-1)), twice the MIC value (25 microg mL(-1)) or ten times the MIC value (125 microg mL(-1)) at 37 degrees C for 30 min or 6 h and the cells were then examined by transmission and scanning electron microscopy. The cell damage evident after 6h incubation was greater than observed after 30 min incubation. Especially, at one half the MIC, no cell damage was evident after 30 min incubation, but damaged cells were observed after 6 h incubation. The proportion of empty cells of P. aeruginosa increased as the concentration of added disinfectant was increased, and the release of intracellular components was also recognized. These results suggest that OPB-2045 acts on the cell membrane and cell wall of P. aeruginosa, and destroys their integrity at the level of the MIC (MBC). With the increase in OPB-2045 concentration and the increase in reaction time, the bactericidal effect increased markedly. Agglutination of the cells was observed at high concentrations of OPB-2045. This indicates that the bactericidal effect at high concentrations of OPB-2045 differs from that at low concentrations. A clear cell-damaging effect against the test strain was recognized which was dependent on the OPB-2045 concentration and the incubation time. From experiments concerning the relationship between the number of surviving bacteria and MIC values in soybean casein digest broth, the decrease in bacterial numbers was found to be dependent on the OPB-2045 concentration. We conclude that it would be a useful contribution to the medical field to supply a new disinfectant to be employed in preventive countermeasures against infection caused by pathogenic bacteria.
The inhibitory effects of creosote and its main components, α‐methoxyphenol and o‐ethylphenol, on production of verotoxin by enterohaemorrhagic Escherichia coli O157 (VTEC E. coli) were investigated. The production of verotoxin by VTEC E. coli was inhibited by the administration of 0·001≈0·1% of creosote or o‐ethylphenol (final concentration). On the other hand, weak inhibition of production of verotoxin was observed with 0·1%α‐methoxyphenol administration. As the inhibitory effects were obtained below Minimal Inhibitory Concentration (MIC) values, these test compounds exerted their effects at the active site of VTEC E. coli cells prior to their production of verotoxin. These findings suggest that pre‐administration of creosote and its main components might prevent human intestinal food poisoning by VTEC E. coli and contribute to maintenance of public health.
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