The Role of Sulphate in the Resistance of Pseudomonas aeruginosa to Antibacterial Agents

Abstract

P. aeruginosa was grown in batch culture in a chemically defined medium and cells depleted of glucose were compared with cells depleted of sulphur in the presence and absence of glucose. During sulphur depletion in the presence of glucose 260nm – absorbing compounds appeared in the medium, the amount being dependent on the sulphur source. The parallel increases in total and viable counts and the failure of potassium to accumulate outside the cell indicates that the appearance of 260nm - absorbing compounds was not due to cell damage. Inhibition by arsenate suggested that glucose was required as an energy source. Sulphur-depleted cells in the presence of glucose are resistant to the action of EDTA whether measured by release of 260nm – absorbing compounds, death or lysis. Sulphur-depleted cells in the absence of glucose and glucose-depleted cells are sensitive to its action. Sulphur-depleted cells in the presence of glucose, unlike glucose-depleted cells, are resistant to the lytic action of polymyxin. However, the polymyxin-induced release of 260nm - absorbing compounds and its bacterial action are increased by sulphur depletion. These latter effects are independent of glucose and, unlike its lytic action are increased by increasing the pH of the test menstruum. Sulphur depletion was associated with increased amounts of outer membrane proteins E and G but no changes in divalent cations were identified. Other variations in outer membrane composition such as lipids and phosphate would not appear to be sufficient to account for the varying sensitivities of these nutrient-depleted cells. The requirement of glucose for resistance to the lytic actions of EDTA and polymyxin and the partial restoration of sensitivity by arsenate, would suggest that in these cells energy is required to maintain an outer-membrane structure which prevents drug-induced lysis.