The extracellular matrix protects Pseudomonas aeruginosa biofilms by limiting the penetration of tobramycin

Abstract

SUMMARY Biofilm cells are less susceptible to antimicrobials than their planktonic counterparts. While this phenomenon is multifactorial, the ability of the biofilm matrix to reduce antibiotic penetration into the biofilm is thought to be of limited importance, as previous studies suggest that antibiotics move fairly rapidly through biofilms. In this study, we monitored the transport of two clinically relevant antibiotics, tobramycin and ciprofloxacin, into non-mucoid P. aeruginosa biofilms. To our surprise, we showed that the positively charged antibiotic tobramycin is sequestered to the biofilm periphery, while the neutral antibiotic ciprofloxacin readily penetrated. We provide evidence that tobramycin in the biofilm periphery both stimulated a localized stress response and killed bacteria in these regions, but not in the underlying biofilm. Although it is unclear which matrix component binds tobramycin, its penetration was increased by the addition of cations in a dose-dependent manner, which led to increased biofilm death. These data suggest that ionic interactions of tobramycin with the biofilm matrix limit its penetration. We propose that tobramycin sequestration at the biofilm periphery is an important mechanism in protecting metabolically active cells that lie just below the zone of sequestration.

Biofilm-Related Infections: Bridging the Gap between Clinical Management and Fundamental Aspects of Recalcitrance toward Antibiotics

“…In contrast, tobramycin was shown to be homogeneously distributed. Conversely, in the case of P. aeruginosa biofilm, tobramycin was shown to exhibit delayed and reduced diffusion in vitro (41,42). Thus, experimental data regarding the diffusion of an antibiotic through the biofilm matrix cannot be extrapolated to another bacterial strain and should be interpreted carefully (Table 1).…”

Growth on mannitol-rich media elicits a genome-wide transcriptional response in Burkholderia multivorans that impacts on multiple virulence traits in an exopolysaccharide-independent manner

“…*P,0.05; **P,0.005. aeruginosa biofilms limits the penetration of tobramycin, such that tobramycin is sequestered by the biofilm periphery (Tseng et al, 2013). If the same is true of B. multivorans biofilms, a greater proportion of biofilm-associated cells would be expected to survive tobramycin challenge in growth conditions that promote thicker biofilms.…”

PslG, a self-produced glycosyl hydrolase, triggers biofilm disassembly by disrupting exopolysaccharide matrix

“…Psl, a repeating pentasaccharide containing D-mannose, D-glucose and L-rhamnose [23], acts as 'molecular glue' to promote bacterial cell-cell and cell-surface interactions and it can form a fiber-like web to enmesh bacterial communities [6,7,17]. This exopolysaccharide also confers resistance of P. aeruginosa biofilms to antibiotics and phagocytic cells [9,[24][25][26]. In P. aeruginosa PAO1 (a common lab strain), Psl is more important than Pel for biofilm microcolony formation and antibiotic resistance [24].…”