The Effect of Growth Environment on Some Biological Properties of Pseudomonas Aeruginosa

Abstract

1. The growth characteristics in batch culture of P.aeruginosa grown in media containing various concentrations of magnesium and glucose has been studied. 2. Media were prepared which contained an excess of all necessary nutrients including oxygen, except the nutrient being studied for its effect on resistance. The effect of glucose or glucose and magnesium depletion on the lysis of P.aeruginosa by EDTA, EGTA and polymyxin was studied. 3 Growth of P.aeruginosa in media depleted of magnesium resulted in cultures that were resistant to lysis by EDTA and polymyxin. 4 Growth of P.aeruginosa in media depleted of magnesium but supplemented with calcium resulted in cultures with restored sensitivity to EDTA and polymyxin. Barium supplementation partially restored the sensitivity to EDTA but had little effect on the resistance to polymyxin. 5 Results from batch culture studies were used to formulate media for studies on carbon and magnesium limited growth in a chemostat. 6 Carbon-limited chemostat cultures of P.aeruginosa became progressively more resistant to lysis by EDTA as the growth rate was decreased. The addition of barium to the medium had no effect whereas the addition of calcium resulted in cells which were sensitive to lysis by EDTA at all growth rates. 7 Magnesium-limited chemostat grown cells were very resistant to lysis by EDTA at all growth rates. The addition of barium to the medium had no effect whereas the addition of calcium rendered the slow growing cells sensitive to EDTA. 8 The sensitivity of both magnesium- and carbon-limited cultures to lysis by polymyxin did not change with growth rate although the carbon-limited cells were the most sensitive. The addition of barium to the media was without effect. The addition of calcium to the media caused an increase in the sensitivity of the magnesium limited cells to this agent. 9 Cells of P.aeruginosa grown in the chemostat were incubated with rabbit peritoneal exudate polymorphonuclear leucocytes and the survival rate assessed. In the presence of normal rabbit serum, slow growing (D = 0.05 hr -1 ) magnesium-limited cells showed considerable survival whereas all other cell types were rapidly killed. 10 The resistance of magnesium-limited cells to killing by cationic proteins isolated from polymorphonuclear leucocytes was shown to be related to growth rate.  All carbon-limited cells were rapidly killed. 11 Agglutination studies with prepared and commercially obtained serum suggested that magnesium-limited cells possessed an exposed O-antigenic side chain in contrast to carbon-limited cells which did not. 12 Heat killed cells from fast and slow growing magnesium and carbon-limited cultures of P.aeruginosa were all considered to be non-toxic to mice. 12 These results formed the basis for proposals made on the effect of growth environment on the cell envelope and on the subsequent action of antimicrobial agents upon it,