Development and Persistence of Antimicrobial Resistance in Pseudomonas aeruginosa : a Longitudinal Observation in Mechanically Ventilated Patients

Abstract

Intubated patients frequently become colonized by Pseudomonas aeruginosa, which is subsequently responsible for ventilator-associated pneumonia. This pathogen readily acquires resistance against available antimicrobials. Depending on the resistance mechanism selected for, resistance might either be lost or persist after removal of the selective pressure. We investigated the rapidity of selection, as well as the persistence, of antimicrobial resistance and determined the underlying mechanisms. We selected 109 prospectively collected P. aeruginosa tracheal isolates from two patients based on their prolonged intubation and colonization periods, during which they had received carbapenem, fluoroquinolone (FQ), or combined ␤-lactam-aminoglycoside therapies. We determined antimicrobial resistance phenotypes by susceptibility testing and used quantitative real-time PCR to measure the expression of resistance determinants. Within 10 days after the initiation of therapy, all treatment regimens selected resistant isolates. Resistance to ␤-lactam and FQ was correlated with ampC and mexC gene expression levels, respectively, whereas imipenem resistance was attributable to decreased oprD expression. Combined ␤-lactam-aminoglycoside resistance was associated with the appearance of small-colony variants. Imipenem and FQ resistance persisted for prolonged times once the selecting antimicrobial treatment had been discontinued. In contrast, resistance to ␤-lactams disappeared rapidly after removal of the selective pressure, to reappear promptly upon renewed exposure. Our results suggest that resistant P. aeruginosa is selected in less than 10 days independently of the antimicrobial class. Different resistance mechanisms lead to the loss or persistence of resistance after the removal of the selecting agent. Even if resistant isolates are not evident upon culture, they may persist in the lung and can be rapidly reselected.

The Challenge of Efflux-Mediated Antibiotic Resistance in Gram-Negative Bacteria

“…Likewise, MexCD-OprJ overproduction was infrequent in ␤-lactam-resistant strains (380,421,423), including those exhibiting increased MICs of the pump substrate cefepime relative to those of ceftazidime (425,455). Microbiological follow-up of one mechanically ventilated patient treated with two substrates of MexCD-OprJ, namely, ciprofloxacin (14 days) and cefepime (19 days), revealed the emergence of nfxB mutants over the time, which accounted for a change of bacteria from S to I or R with regard to their susceptibility to fluoroquinolones (CLSI breakpoints) (475). Interestingly, the overexpression of MexCD-OprJ, as with that of MexAB-OprM or MexXY, occurred in 60% of carbapenem-resistant clinical isolates (476).…”

Bacterial recombination promotes the evolution of multi-drug-resistance in functionally diverse populations

“…However, the relative importance of mutation and recombination in the evolution of MDR, and in bacterial adaptation generally, remains unclear. Genomic analyses of clinical isolates show that many known resistance genes probably spread via horizontal gene transfer between different species [6][7][8], yet many clinical pathogens also evolve MDR de novo through novel genetic changes [9,10]. Evolution experiments offer a useful approach to uncover the factors determining the evolution of resistance, but most experiments have studied clonal populations without any contribution of recombination [4].…”

Evaluation of the βLACTA Test, a Novel Commercial Chromogenic Test for Rapid Detection of Ceftazidime-Nonsusceptible Pseudomonas aeruginosa Isolates

“…In nosocomial infections with Pseudomonas aeruginosa, multidrug resistance (including resistance to CAZ) usually results from previous antibiotic selective pressure leading to chromosomal AmpC cephalosporinase and/or efflux pump overexpression (12) or from the acquisition of various transferable ␤-lactamases. According to our results, a negative BLT result accurately predicts in vitro susceptibility of P. aeruginosa to CAZ and would allow the continuation or initiation of treatment with this agent in case of infection.…”