An Eye to a Kill: Using Predatory Bacteria to Control Gram-Negative Pathogens Associated with Ocular Infections

Ocular infections are a leading cause of vision loss. It has been previously suggested that predatory prokaryotes might be used as live antibiotics to control infections. In this study, Pseudomonas aeruginosa and Serratia marcescens ocular isolates were exposed to the predatory bacteria Micavibrio aeruginosavorus and Bdellovibrio bacteriovorus. All tested S. marcescens isolates were susceptible to predation by B. bacteriovorus strains 109J and HD100. Seven of the 10 P. aeruginosa isolates were susceptible to predation by B. bacteriovorus 109J with 80% being attacked by M. aeruginosavorus. All of the 19 tested isolates were found to be sensitive to at least one predator. To further investigate the effect of the predators on eukaryotic cells, human corneal-limbal epithelial (HCLE) cells were exposed to high concentrations of the predators. Cytotoxicity assays demonstrated that predatory bacteria do not damage ocular surface cells in vitro whereas the P. aeruginosa used as a positive control was highly toxic. Furthermore, no increase in the production of the proinflammatory cytokines IL-8 and TNF-alpha was measured in HCLE cells after exposure to the predators. Finally, injection of high concentration of predatory bacteria into the hemocoel of Galleria mellonella, an established model system used to study microbial pathogenesis, did not result in any measurable negative effect to the host. Our results suggest that predatory bacteria could be considered in the near future as a safe topical bio-control agent to treat ocular infections. © 2013 Shanks et al

Inflammatory response of human corneal-limbal epithelial cells to predatory bacteria <i>in vitro</i>.

<p>Pro-inflammatory cytokines IL-8 (panel A) and TNF-α (panel B) were measured using ELISA assays. Cell supernatants taken from HCLE cells after 4 hrs of incubation with positive control <i>Pseudomonas aeruginosa</i> strain PA14 (average MOI  =  111), detergent lysis (LYSIS), medium only negative control (DNB), and experimental strains <i>B. bacteriovorus</i> strain 109J (avgerage MOI  =  4720), <i>B. bacteriovorus</i> strain HD100 (average MOI  =  1039), and <i>M. aeruginosavorus</i> (Mica, average MOI  =  853). Total independent data points from 2 experiments are shown. Asterisks indicate significant differences (p<0.001, ANOVA with Tukey's post-test). Only PA14 was significantly different than MOCK. Error bars indicate one standard deviation.</p

Cytotoxicity to human corneal-limbal epithelial cells <i>in vitro</i>.

<p>Alamar blue vital stain was used to measure cytotoxicity from positive control <i>P. aeruginosa</i> strain PA14 (average MOI  =  111), detergent lysis (LYSIS), medium only negative control (MOCK), and experimental strains <i>B</i>. <i>bacteriovorus</i> strain 109J (average MOI  =  4720), <i>B. bacteriovorus</i> strain HD100 (average MOI  =  1039), and <i>M. aeruginosavorus</i> (Mica, average MOI  =  853). HCLE viability was measured after 4 h (A) and 24 h (B) of exposure. Total independent data points from 4 experiments are shown. Asterisks indicate significant differences (p<0.001, ANOVA with Tukey's post-test). Only PA14 was significantly different than MOCK. Error bars indicate one standard deviation.</p