Electron microscope study of effect of benzalkonium chloride and edetate disodium on cell envelope of Pseudomonas aeruginosa.

Electron micrographs of Pseudomonas aeruginosa grown in nutrient broth or broth containing subinhibitory concentrations of benzalkonium chloride indicate that benzalkonium chloride at 50 and 100 mug/ml strips off the outer cell membrane. Cells grown in the presence of edetate disodium, 50-100 mug/ml had convoluted surfaces (wavy in cross section). Cells damaged by growing on nutrient agar containing benzalkonium (200 mug/ml), when subsequently grown for 16 hr in nutrient broth, produced cells with apparently normal outer lavers. Similar cells grown on nutrient agar plus benzalkonium (500 mug/ml) when grown for 16 hr in nutrient broth had normal resistance to edetate disodium lysis, but cells grown overnight in broth plus benzalkonium (500 mug/ml) showed increased sensitivity to edetate disodium lysis. Cells grown on nutrient agar in the presence of benzalkonium (800 mug/ml) grew in broth plus benzalkonium (10 mug/ml) without stripping of their external membrane, but replicate inocula into broth plus benzalkonium (10 mug/ml) and edetate disodium (50 mug/ml) produced cells with structural damage to the outer lavers of the cell envelope.