Dioctadecyldimethylammonium bromide (DODAB), a bilayer-forming synthetic amphiphile with antibacterial properties, also affects viability of Candida albicans. For C. albicans, simultaneous determination of cell viability and electrophoretic mobility as a function of DODAB concentration yields a very good correlation between cell surface charge and cell viability. Upon increasing DODAB concentration, the cell surface charge decreases and changes its sign to yield positively charged cells. However, in contrast to the DODAB bactericidal property, the amphiphile effect on fungus over 1 h of interaction time is only fungistatic at 1 mM DODAB and ca. 10 6 cells/mL. Nevertheless, solubilization of fungicides in DODAB dispersions prepared by sonication causes complete loss of cell viability. Amphotericin B (AB) or miconazole (M) solubilization in the DODAB bilayer leads to 100% cell death, though the drug and DODAB effects are independent. Cell and DODAB bilayer membranes compete for AB or M solubilization with the amphiphile bilayer controlling drug release to the cell membrane. 0.1 mM DODAB plus AB or M concentration of 2 and 20 µg/mL, respectively, yielded 0% of cell viability for C. albicans (2 × 10 6 cells/mL) over an interaction time of 24 h. The cationic liposomes by themselves yielded ca. 20% viability under similar conditions. The full potential of these cytotoxic cationic bilayers to control release and cytotoxicity of drugs remains hitherto unexplored.

The bactericidal effect of dioctadecyldimethylammonium bromide (DODAB), a liposome forming synthetic amphiphile, is further evaluated for Escherichia coli , Salmonella typhimurium , Pseudomonas aeruginosa , and Staphylococcus aureus in order to establish susceptibilities of different bacteria species towards DODAB at a fixed viable bacteria concentration (2.5 ؋ 10 7 viable bacteria/mL). For the four species, susceptibility towards DODAB increases from E. coli to S. aureus in the order above. Typically, cell viability decreases to 5% over 1 h of interaction time at DODAB concentrations equal to 50 and 5 M for E. coli and S. aureus , respectively. At charge neutralization of the bacterial cell, bacteria flocculation by DODAB vesicles is shown to be a diffusion-controlled process. Bacteria flocculation does not yield underestimated counts of colony forming units possibly because dilution procedures done before plating cause deflocculation. The effect of vesicle size on cell viability demonstrates that large vesicles, due to their higher affinity constant for the bacteria (45.20 M ؊ 1 ) relative to the small vesicles (0.14 M ؊ 1 ), kill E. coli at smaller DODAB concentrations. For E. coli and S. aureus , simultaneous determination of cell viability and electrophoretic mobility as a function of DODAB concentration yields a very good correlation between cell surface charge and cell viability. Negatively charged cells are 100% viable whereas positively charged cells do not survive. The results show a clear correlation between simple adsorption of entire vesicles generating a positive charge on the cell surfaces and cell death. -Campanhã, M. T. N., E. M. Mamizuka, and A. M. Carmona-Ribeiro. Interactions between cationic liposomes and bacteria: the physical-chemistry of the bactericidal action.

Escherichia coli is the most common causative agent of urinary tract infection (UTI), and diagnosing this infection usually relies on bacteriologic methods. Nevertheless, screening methods can be useful for a rapid presumptive diagnosis even though some of these screening methods have low sensitivity or are expensive. To investigate a possible new alternative approach, an antigen-based immunoassay--enzyme-linked immunoelectrodiffusion assay (ELIEDA)--was standardized for screening for this bacterial infection. Combining counter-immunoelectrophoresis with an immunoenzymatic assay, the ELIEDA requires concentrated urine specimens, a cellulose acetate membrane, polyclonal antibodies to E. coli raised in rabbits, and peroxidase-labeled sheep antibodies to rabbit immunoglobulin G (IgG). This ELIEDA technique was evaluated using 244 urine specimens, 76 of them with E. coli, 47 with heterologous bacteria, and 121 without bacteria. In comparison to bacteriologic methods, the sensitivity, specificity, and positive and negative predictive values for the ELIEDA were 93.4%, 98.2%, 95.9%, and 97.1%, respectively. The data obtained suggest that this assay is useful for routine diagnostic screening for UTI caused by E. coli. In addition, since the ELIEDA stained membranes can be stored, this assay makes retrospective studies possible.