title: Resistance emergence mechanism and mechanism of resistance suppression by tobramycin for cefepime for Pseudomonas aeruginosa.
abstract: The panoply of resistance mechanisms in Pseudomonas aeruginosa makes resistance suppression difficult. Defining optimal regimens is critical. Cefepime is a cephalosporin whose 3' side chain provides some stability against AmpC β-lactamases. We examined the activity of cefepime against P. aeruginosa wild-type strain PAO1 and its isogenic AmpC stably derepressed mutant in our hollow-fiber infection model. Dose-ranging studies demonstrated complete failure with resistance emergence (both isolates). Inoculum range studies demonstrated ultimate failure for all inocula. Lower inocula failed last (10 days to 2 weeks). Addition of a β-lactamase inhibitor suppressed resistance even with the stably derepressed isolate. Tobramycin combination studies demonstrated resistance suppression in both the wild-type and the stably derepressed isolates. Quantitating the RNA message by quantitative PCR demonstrated that tobramycin decreased the message relative to that in cefepime-alone experiments. Western blotting with AmpC-specific antibody for P. aeruginosa demonstrated decreased expression. We concluded that suppression of β-lactamase expression by tobramycin (a protein synthesis inhibitor) was at least part of the mechanism behind resistance suppression. Monte Carlo simulation demonstrated that a regimen of 2 g of cefepime every 8 h plus 7 mg/kg of body weight of tobramycin daily would provide robust resistance suppression for Pseudomonas isolates with cefepime MIC values up to 8 mg/liter and tobramycin MIC values up to 1 mg/liter. For P. aeruginosa resistance suppression, combination therapy is critical.
authors: Ordway Research Institute, Albany, New York, USA. gdrusano@ufl.edu
authors: G L
authors: GL
authors: Drusano
authors: Robert A
authors: RA
authors: Bonomo
authors: Nadzeya
authors: N
authors: Bahniuk
authors: Juergen B
authors: JB
authors: Bulitta
authors: Brian
authors: B
authors: Vanscoy
authors: Holland
authors: H
authors: Defiglio
authors: Steven
authors: S
authors: Fikes
authors: David
authors: D
authors: Brown
authors: Sarah M
authors: SM
authors: Drawz
authors: Robert
authors: R
authors: Kulawy
authors: Arnold
authors: A
authors: Louie
mesh_terms: D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D015153:Blotting, Western; D000077723:Cefepime; D002511:Cephalosporins / Q000493:pharmacokinetics / Q000494:pharmacology*; D003198:Computer Simulation; D004334:Drug Administration Schedule; D004347:Drug Interactions; D024881:Drug Resistance, Bacterial / Q000187:drug effects*; D015964:Gene Expression Regulation, Bacterial; D008826:Microbial Sensitivity Tests; D008954:Models, Biological; D009010:Monte Carlo Method; D011500:Protein Synthesis Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology; D011552:Pseudomonas Infections / Q000188:drug therapy* / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014031:Tobramycin / Q000493:pharmacokinetics*; D001618:beta-Lactamases / Q000172:deficiency / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002511:Cephalosporins; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D000077723:Cefepime; C048795:AmpC beta-lactamases; D001618:beta-Lactamases; D014031:Tobramycin