Antipseudomonal Agents Exhibit Differential Pharmacodynamic Interactions with Human Polymorphonuclear Leukocytes against Established Biofilms of Pseudomonas aeruginosa

Abstract

bPseudomonas aeruginosa is the most common pathogen infecting the lower respiratory tract of cystic fibrosis (CF) patients, where it forms tracheobronchial biofilms. Pseudomonas biofilms are refractory to antibacterials and to phagocytic cells with innate immunity, leading to refractory infection. Little is known about the interaction between antipseudomonal agents and phagocytic cells in eradication of P. aeruginosa biofilms. Herein, we investigated the capacity of three antipseudomonal agents, amikacin (AMK), ceftazidime (CAZ), and ciprofloxacin (CIP), to interact with human polymorphonuclear leukocytes (PMNs) against biofilms and planktonic cells of P. aeruginosa isolates recovered from sputa of CF patients. Three of the isolates were resistant and three were susceptible to each of these antibiotics. The concentrations studied (2, 8, and 32 mg/liter) were subinhibitory for biofilms of resistant isolates, whereas for biofilms of susceptible isolates, they ranged between sub-MIC and 2 ؋ MIC values. The activity of each antibiotic alone or in combination with human PMNs against 48-h mature biofilms or planktonic cells was determined by XTT [2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide] assay. All combinations of AMK with PMNs resulted in synergistic or additive effects against planktonic cells and biofilms of P. aeruginosa isolates compared to each component alone. More than 75% of CAZ combinations exhibited additive interactions against biofilms of P. aeruginosa isolates, whereas CIP had mostly antagonistic interaction or no interaction with PMNs against biofilms of P. aeruginosa. Our findings demonstrate a greater positive interaction between AMK with PMNs than that observed for CAZ and especially CIP against isolates of P. aeruginosa from the respiratory tract of CF patients. Pseudomonas aeruginosa causes acute and chronic infections predominantly associated with compromised innate host defenses (1, 2). In patients with cystic fibrosis (CF), chronic P. aeruginosa infection of the lower respiratory tract is associated with excessive morbidity and mortality, as more than 80% of these patients succumb to respiratory failure (3, 4). A critical virulence trait of this pathogen that dominates in the CF lung is its capacity to form biofilms, a characteristic that has been linked to antimicrobial resistance and host defense evasion (5, 6). Chronic pulmonary infections arise because host responses are ineffective against biofilms (7). However, virulence factors that depend on the cellto-cell communication system of P. aeruginosa are shown to have a major role as a defense against polymorphonuclear leukocytes (PMNs) (8-10).Biofilms are surface-attached structured networks of aggregated bacteria embedded in a self-produced matrix composed of polysaccharides, protein, and DNA. These aggregates can resist high concentrations of antimicrobial agents that would efficiently eliminate the single-cell planktonic phenotype (11-13).Exposure of bacteria to subinhibitory antibiotic concentrations (sub-MI...

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