Emergence of Colistin Resistance in Enterobacteriaceae after the Introduction of Selective Digestive Tract Decontamination in an Intensive Care Unit

Abstract

Selective decontamination of the digestive tract (SDD) selectively eradicates aerobic Gram-negative bacteria (AGNB) by the enteral administration of oral nonabsorbable antimicrobial agents, i.e., colistin and tobramycin. We retrospectively investigated the impact of SDD, applied for 5 years as part of an infection control program for the control of an outbreak with extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae in an intensive care unit (ICU), on resistance among AGNB. Colistin MICs were determined on stored ESBL-producing K. pneumoniae isolates using the Etest. The occurrence of both tobramycin resistance among pathogens intrinsically resistant to colistin (CIR) and bacteremia caused by ESBL-producing K. pneumoniae and CIR were investigated. Of the 134 retested ESBL-producing K. pneumoniae isolates, 28 were isolated before SDD was started, and all had MICs of <1.5 mg/liter. For the remaining 106 isolated after starting SDD, MICs ranged between 0.5 and 24 mg/liter. Tobramycin-resistant CIR isolates were found sporadically before the introduction of SDD, but their prevalence increased immediately afterward. Segmented regression analysis showed a highly significant relationship between SDD and resistance to tobramycin. Five patients were identified with bacteremia caused by ESBL-producing K. pneumoniae before SDD and 9 patients thereafter. No bacteremia caused by CIR was found before SDD, but its occurrence increased to 26 after the introduction of SDD. In conclusion, colistin resistance among ESBL-producing K. pneumoniae isolates emerged rapidly after SDD. In addition, both the occurrence and the proportion of tobramycin resistance among CIR increased under the use of SDD. SDD should not be applied in outbreak settings when resistant bacteria are prevalent.

Polymyxins: Antibacterial Activity, Susceptibility Testing, and Resistance Mechanisms Encoded by Plasmids or Chromosomes

“…Important increases of colistin resistance rates among ESBL-producing K. pneumoniae isolates (from 0 to 71% and from 11.1 to 75%) were reported after the introduction of selective digestive tract decontamination in two intensive care units (212,213). Moreover, this decontamination failed to prevent colonization by ESBL-producing Enterobacteriaceae, and such a strategy should be abandoned.…”

Colistin Resistance during Selective Digestive Tract Decontamination Is Uncommon

“…e read the report entitled "Emergence of colistin resistance in Enterobacteriaceae after the introduction of selective digestive tract decontamination in an intensive care unit" by Halaby and colleagues (1). Although we are quite familiar with the issue of selective digestive decontamination (SDD) and resistance (2)(3)(4), this report on the subject raises some concerns.…”

Induction and nosocomial dissemination of carbapenem and polymyxin-resistant Klebsiella pneumoniae

“…The highest MIC was observed in an isolate from case 1, who received polymyxin for a longer period (25 + 14 days). The emergence of polymyxin B-resistant isolates has been observed during treatment with this drug for KPC-producing K. pneumoniae infection or colonization probably due to the selective pressure of polymyxin B on the heterogeneous bacterial population (13) . An in vitro study of multidrug-resistant colistin-susceptible K. pneumoniae revealed colistin had a rapid bactericidal effect albeit a low post-antibiotic effect; bacterial regrowth was attributed to the heteroresistance phenomena, which was detected in 15 of 16 isolates (14) .…”