Electron-microscope studies of the effect of subinhibitory concentrations of phenylethanol and polysorbate 80 on Pseudomonas aeruginosa‘sensitive’ and ‘resilient’ to benzalkonium chloride

Abstract

935creased wetting and dispersion of the powder such that at the highest concentrations used the powder was dispersed to a semi-colloidal state. Short & others (1972), studying similar systems found a pronounced maximum dissolution rate near to the cmc while we did not observe a maximum.Solubilities of hydrocortisone are shown in Fig. 2. Solulan 16 and 25 are ethoxylated lacohol fractions of lanolin containing respectively 16 and 25 moles of ethylene oxide. Mulley (1964) has shown that altering the ethylene oxide chain number does not alter the general shape of solubility curves hence the solubility of hydrocortisone was determined in Solulan 25 only. Similarly there are only two data points for Solulan 16 dissolution (Fig. 1). As these fit the Solulan 25 line, any further points could be expected to follow the trend. The rate of increase of solubility relative to solubility in 0.1 M HCI is much less than for relative rate of increase of initial dissolution rate. This indicates that changing solubility is unlikely to be a major factor in increased dissolution rates in these systems. The main factor thus appears to be increased dispersion and wetting of the powder. That wetting and dispersion occur appreciably only above the cmc is unexpected. However, on the basis of cmc values, assumptions about the molecular weight of surfactants and of the particle size of hydrocortisone, it is possible to calculate the approximate surface area of the particles and the approximate surface area of surfactant molecules at the cmc. Comparison shows that even if all surfactant molecules were adsorbed they would cover less than 1 % of the surface of the hydrocortisone particles. Thus concentrations of surfactant well above the cmc are required to permit sufficient to be adsorbed onto the hydrocortisone particles to give adequate wetting. Solulans, which have a ring structure similar to hydrocortisone, might be expected to be adsorbed more strongly on hydrocortisone than polysorbate. The observed measurements d o not indicate any significant difference.

Polysorbate 80 Inhibition of Pseudomonas aeruginosa Biofilm Formation and Its Cleavage by the Secreted Lipase LipA

“…While it possesses little antimi-crobial activity alone, PS80 can increase bacterial cell permeability (4) and enhance the antimicrobial activity of a variety of antibiotics against P. aeruginosa, including chlorhexidine diacetate, benzalkonium chloride, and polymyxin B sulfate (2,3,5,27,28). On the basis of these findings and studies indicating that PS80 lyses spheroplasts (gram-negative bacteria in which the outer membrane has been removed), Brown and colleagues proposed that PS80 is primarily active against the inner membrane of P. aeruginosa (2).…”