Neutrophil lysis by S. epidermidis PSM peptides and culture filtrates of PSMδ-expression strains.
(A) Neutrophil (PMN) lysis by synthetic, N-formylated PSM peptides at 10 µg/ml was determined by measuring release of LDH (incubation time, 1 h). PSMα3 (S. aureus) was used as a comparison at the same concentration. (B) Neutrophil lysis using supernatants (18-h cultures) of a PSMδ-over-expressing agr-negative (lacking intrinsic PSM production) and corresponding control strains (incubation time, 6 h). pTXpsmδ, pTX construct expressing PSMδ; pTX16, control plasmid. Strains were grown in TSB with 0.5% xylose and 12.5 µg/ml tetracycline. **, p<0.01, paired t-tests. Blue bars, PSMδ concentration in the culture filtrates relative to that in the 1457 wild-type (set to 100%).