Effects of Divalent Metal Cations in the Growth Medium upon Sensitivity of Batch‐grown Pseudomonas aeruginosa to EDTA or Polymyxin B

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Abstract
The sensitivity of batch grown Pseudomonas aeruginosa to ethylenediaminetetraacetic acid (EDTA), ethyleneglycol‐bis(2‐aminoethyl ether)‐N, N‐tetraacetic acid (EGTA) and to polymyxin depended upon the nature and concentration of divalent metal cations (Ca2+, Mg2+, Ba2+, Mn2+, Sr2+, Zn2+, Fe2+, Al3+) present in the simple salts‐glucose growth medium. Sensitivity to the antibacterial agents was measured in terms of per cent decrease in optical density which was proportional to total count. The rate of decrease in optical density and the per cent decrease after a given time were proportional to the cation content of the growth medium. The lytic action of the agents correlated to some extent with the stability constants of the cation for the two chelating agents.The data support the theory that EDTA and polymyxin both act initially at a common site of action, namely the Mg2+ and Ca2+ cross bridges that stabilize components of the outer membrane.