Hyperbaric Oxygen Sensitizes Anoxic Pseudomonas aeruginosa Biofilm to Ciprofloxacin

Abstract

Chronic Pseudomonas aeruginosa lung infection is characterized by the presence of endobronchial antibiotic-tolerant biofilm, which is subject to strong oxygen (O2) depletion due to the activity of surrounding polymorphonuclear leukocytes. The exact mechanisms affecting the antibiotic susceptibility of biofilms remain unclear, but accumulating evidence suggests that the efficacy of several bactericidal antibiotics is enhanced by stimulation of aerobic respiration of pathogens, while lack of O2 increases their tolerance. In fact, the bactericidal effect of several antibiotics depends on active aerobic metabolism activity and the endogenous formation of reactive O2 radicals (ROS). In this study, we aimed to apply hyperbaric oxygen treatment (HBOT) to sensitize anoxic P. aeruginosa agarose biofilms established to mimic situations with intense O2 consumption by the host response in the cystic fibrosis (CF) lung. Application of HBOT resulted in enhanced bactericidal activity of ciprofloxacin at clinically relevant durations and was accompanied by indications of restored aerobic respiration, involvement of endogenous lethal oxidative stress, and increased bacterial growth. The findings highlight that oxygenation by HBOT improves the bactericidal activity of ciprofloxacin on P. aeruginosa biofilm and suggest that bacterial biofilms are sensitized to antibiotics by supplying hyperbaric O2.

Non‐invasive imaging of oxygen concentration in a complex in vitro biofilm infection model using 19F MRI: Persistence of an oxygen sink despite prolonged antibiotic therapy

“…In the experimental condition, the bacteria were allowed 20 h of growth to establish a biofilm before GEN administration. Plate counts revealed that over this period bacterial counts in the inoculated bead rose from the initial inoculum concentration of ~log 10 5.4 colony-forming units per milliliter to about log 10 9.2 colony-forming units per milliliter ( Figure 5), while beads adjacent to the inoculated bead experienced a growth from 0 to log 10 4.4 colony-forming units per milliliter (P < .001 and P = .015, respectively). After this point, in contrast to the rapid depletion of oxygen in the absence of antibiotic, the onset of GEN exposure coincided with a "freezing" of the oxygen sink, characterized by ongoing oxygen usage but a complete lack of sink spatial expansion.…”

The Consequences of Being in an Infectious Biofilm: Microenvironmental Conditions Governing Antibiotic Tolerance

“…Another promising approach is to supply extra O 2 to hypoxic environments [ 41 , 107 , 108 ] to overcome the antibiotic tolerance in established biofilms where dormant bacteria are present. Hyperbaric O 2 treatment (HBOT) has previously been used as an adjuvant to ciprofloxacin on P. aeruginosa [ 109 , 110 ], but the underlying mechanism still needs to be investigated thoroughly.…”

An integrated model system to gain mechanistic insights into biofilm formation and antimicrobial resistance development inPseudomonas aeruginosaMPAO1

“…Increased antimicrobial tolerance, a fundamental property of biofilms [12] is well-studied [13] and four mechanisms play a major role: (i) under nutrient-limited conditions in biofilms, P. aeruginosa expresses phenotypic variants, i.e., dormant cells that are less susceptible to antibiotics which target actively dividing cells [14]; (ii) P. aeruginosa form a protective extracellular matrix composed of polysaccharides, proteins and DNA that limits the diffusion of antimicrobial substances or sequesters them, such that biofilm cells experience a decreased antimicrobial dosage [15]; (iii) anoxic conditions exist within the biofilm limiting the efficacy of antibiotics that require aerobic metabolic activity and the generation of reactive oxygen species [16]; (iv) sub-inhibitory concentrations of antibiotics induce increased rates of mutation, recombination and lateral transfer. The mutation rate in biofilms has been reported to be up to 100 times higher than in planktonic cells [17], significantly accelerating the development of antibiotic resistant mutants.…”