Single and Combination Antibiotic Susceptibilities of Planktonic, Adherent, and Biofilm-Grown Pseudomonas aeruginosa Isolates Cultured from Sputa of Adults with Cystic Fibrosis

Abstract

Evidence suggests that Pseudomonas aeruginosa bacteria form biofilms within the airways of adults with cystic fibrosis (CF). The objective of this study was to determine whether clinical isolates of P. aeruginosa recovered from adults with CF have similar susceptibilities to individual antibiotics and to antibiotic combinations when grown as adherent monolayers or as biofilms compared to when they are grown using planktonic methods. Twelve multiresistant P. aeruginosa isolates, one mucoid and one nonmucoid from each of six CF patients, were grown conventionally under planktonic conditions, as adherent bacterial monolayers, and as biofilms. Each bacterial isolate remained genotypically identical despite being cultured under planktonic, adherent, or biofilm growth conditions. Isolates grown as adherent monolayers and as biofilms were less susceptible to bactericidal killing by individual antibiotics compared to those grown planktonically. More importantly, biofilm-grown bacteria, but not adherent monolayer-grown bacteria, were significantly less susceptible to two-and three-drug combinations of antibiotics than were planktonically grown bacteria (P ‫؍‬ 0.005). We conclude that biofilm-grown bacteria derived from patients with CF show decreased susceptibility to the bactericidal effects of antibiotic combinations than do adherent and planktonically grown bacteria.

Cis-2-decenoic Acid Inhibits S. aureus Growth and Biofilm In Vitro: A Pilot Study

“…Since antibiotics have greater bactericidal efficacy against planktonic bacteria than biofilm [1,7,40], the combination of C2DA with traditional antibiotics could have improved bactericidal efficacy and infection prevention therapies [16]. The combination of daptomycin or vancomycin with C2DA slightly enhanced the antibiofilm effects, but the combination of linezolid resulted in biofilm inhibition at concentrations two to 16 times lower than for either antimicrobial alone.…”

Sputum versus bronchoscopy for diagnosis of Pseudomonas aeruginosa biofilms in cystic fibrosis

“…Single and combination antibiotic susceptibility testing of P. aeruginosa, grown as biofilms, has been previously validated and shown to be reproducible [7,21].…”

“…A rocking table was used to produce shear forces across each peg, resulting in the formation of equivalent biofilms at each peg site. The current authors have previously shown by electron microscopy that this method results in biofilm growth on the pegs [7]. The biofilm culture was then transferred to a standard 96-well plate in which dilutions of antibiotics had been prepared and then incubated overnight at 35uC in ambient air.…”

“…One problem with relying on sputum samples to guide therapy is that biofilm bacteria may not be adequately sampled via sputum, since sputum expectoration only samples P. aeruginosa that have detached and dispersed from the airway biofilm [5,6]. In vitro studies have shown that biofilm-forming P. aeruginosa are significantly less susceptible to antibiotics compared to nonadherent forms [3,7]. However, studies have not previously been done to determine whether bacteria retrieved from sputum are more susceptible to antibiotics compared to bacteria retrieved directly from the airway biofilm.…”

Factors associated with infection by Pseudomonas aeruginosa in adult cystic fibrosis

“…In other words, alternative mechanisms must have been operational in the clustered strain to lead to mucoidy [20]. Multiple and diverse bacterial factors associated with the ability of cross-infecting P. aeruginosa strains to successfully establish persistent infection in other hosts are conceivable including: an improved ability to aerosolise [9]; a propensity to infect sheltered extrapulmonary sites [21] or adhere to CF mucosal surfaces [22]; a better ability to prosper in the abnormally anaerobic environment of the airway surface liquid typical of older CF patients; an increased tendency to form biofilms in the respiratory tract; or increased intrinsic antibiotic resistance [3] (in turn related to the propensity to form biofilms) [23]. Further work is required to better define these bacterium-specific factors.…”