Effects of Ca2+ ions on survival, growth, and cell size in Serratia marcescens SMG40 exposed to mecillinam.
Serratia marcescens strain SMG40 is sensitive to mecillinam killing at concentrations approaching those required for rod-to-sphere conversion. After a 1 h exposure to mecillinam, the type of response was found to depend on the conditions of post-incubation. Whereas they lysed soon after transfer to a tenfold-diluted broth, treated cells stopped dividing and enlarged impressively without immediate lysis when they were transferred to a complete low-agar medium and incubated at 30 degrees C. More remarkably, the presence of Ca2+ cations in any post-incubation medium definitely protected treated cells from lysis, enabled them to divide as spheres, and prevented enlargement. These survival-promoting and size-limiting effects were reversible upon elimination of Ca2+ from the medium. They were observable at far lower ionic concentrations than those required for osmotic stabilization. The growth rate depended on the Ca2+ concentration (from 10 microM) and on the presence of other supplements. Na+ cations also exerted a protective effect but acted differently from Ca2+ ions; the effects of Na+ and Ca2+ ions appeared as synergistic. A physiological activity of calcium is suggested for this bacterial strain, resulting in a RodA-like mecillinam resistant phenotype.
Laboratory of Microbiology, Free University of Brussels School of Medicine, Belgium.
J P
JP
Gratia
D000560:Amdinocillin / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D004357:Drug Synergism; D007700:Kinetics; D016014:Linear Models; D008826:Microbial Sensitivity Tests; D008903:Minerals / Q000494:pharmacology; D009994:Osmolar Concentration; D010406:Penicillins / Q000494:pharmacology*; D012706:Serratia marcescens / Q000187:drug effects* / Q000254:growth & development / Q000648:ultrastructure; D012964:Sodium / Q000494:pharmacology
D008903:Minerals; D010406:Penicillins; D012964:Sodium; D002118:Calcium; D000560:Amdinocillin