Production of Poly-γ-Glutamic Acid (γ-PGA) by Clinical Isolates of Staphylococcus Epidermidis

Abstract

Background and Objective: Poly-γ-glutamic acid (γ-PGA) is a constituent of the Bacillus anthracis capsule and a potential virulence factor of S. epidermidis. In this study, a methodology for the isolation, purification and quantification of γ-PGA in the isolates was adapted. In addition, the fate of the produced γ-PGA and its antiphagocytic activity were investigated. Methods: The capB gene was investigated by the PCR method in 50 isolates of S. epidermidis. A modified methodology was used for the extraction, purification, and quantification of γ-PGA using Cetyltrimethylammonium Bromide (CTAB) solution. The fate of γ-PGA was determined in Tryptic Soy Broth (TSB) medium, as well as the effect of ethanol, NaCl and KCl on the induction of the polymer production. The ability of neutrophils to phagocyte both FITC-labeled latex particles in the presence of free γ-PGA and S. epidermidis with and without anchored γ-PGA was evaluated by cytometry. Results: The production of γ-PGA was detected in 40 isolates; all of them were capB gene carriers. Free γ-PGA was detected and in the strain, the amount of released γ-PGA in the supernatant was 67% greater than the cell anchored γ-PGA. Phagocytosis tests performed with one γ-PGA producer isolate showed a significant reduction in neutrophil internalization. Conclusion: The adapted methodology was able to detect γ-PGA in the isolates studied. In addition to being found attached to the cell wall, it was demonstrated in this study that γ-PGA can also be found in the culture supernatant. Free γ-PGA did not determine a reduction in the internalization of latex by neutrophils, but cells with anchored γ-PGA showed significant protection against phagocytosis.