MECHANISMS OF FAILURE TO DECONTAMINATE THE GUT WITH POLYMIXIN-E, GENTAMICIN AND AMPHOTERICIN-B IN PATIENTS IN INTENSIVE-CARE

The objective of the present work was to assess the possible mechanism s of the poor efficiency of selective decontamination of the digestive tract (SDD) in medical and surgical intensive care unit (ICU) patient s. Sixty-four consecutive mechanically ventilated patients received gu t decontamination with polymixin E, gentamicin and amphotericin B via a nasogastric tube and were assessed for oropharyngeal, gastric and fe cal colonization and for the presence of each antibiotic in the stomac h and feces. A decrease in fecal colonization with Escherichia coli wa s observed over 20 days but not with other gram-negative bacteria or g ram-positive cocci. Fifteen and 26 % of the fecal colonizing gram-nega tive bacteria were resistant to polymixin E and gentamicin, respective ly, at admission. These proportions increased to up to 50 % after 16 d ays of treatment. Although 50 % of staphylococci were initially sensit ive to gentamicin, all strains were resistant to this drug after four days of SDD. Both antibiotics were found in concentrations of less tha n 20 mug/g in 11 of 38 stools. Of these 38 stools, nine were not conta minated, 20 were colonized with resistant bacteria and 16 with strains sensitive to one antibiotic present in the stool. Therefore, the poor efficiency of gut decontamination observed was probably due to the gr eat proportion of resistant strains on admission of the patients, to t he selection of such resistant strains with SDD, to poor intestinal tr ansit of the antibiotics, and to inactivation of the drugs by the fece s. These results support stringent monitoring of fecal colonization in patients undergoing SDD in order to detect the fecal carriage of gram -positive and multiresistant gram-negative bacteria.