THE EFFECTS OF ENVIRONMENTAL-CONDITIONS ON THE IN-VITRO ACTIVITY OF SELECTED ANTIMICROBIAL AGENTS AGAINST ESCHERICHIA-COLI

Various environmental conditions Likely to be encountered at a nidus o f infection were evaluated for their effect on selected classes of ant imicrobial agents. The minimum inhibitory concentration (MIC) of sever al aminoglycosides (apramycin, kanamycin, gentamicin, tobramycin, amik acin), tetracycline, and chloramphenicol for five strains of E, coli w ere unchanged by temperature (35 degrees-39.5 degrees C), atmosphere ( aerobic to anaerobic), pH > 7, NaCl concentration (up to 150 mM), zinc concentration (up to 50 mM), and manganese (up to 10 mM). However, th e aminoglycoside MICs were increased up to fivefold at pH < 6.5. Magne sium and calcium ion concentrations >10 mM and ferric iron concentrati ons greater than or equal to 10 mM increased aminoglycoside MICs from 3.66- to 8-fold. Tetracycline MICs were increased 1.2 to 6.5-fold when the concentration of magnesium or calcium was greater than or equal t o 10 mM. The results of this in vitro study might provide insight into the effects of local in vivo environmental conditions on several clas ses of antimicrobial agents.