Antibiotics Stimulate Formation of Vesicles in in both Phage-Dependent and -Independent Fashions and via Different Routes.

Bacterial membrane vesicle research has so far focused mainly on Gram-negative bacteria. Only recently have Gram-positive bacteria been demonstrated to produce and release extracellular membrane vesicles (MVs) that contribute to bacterial virulence. Although treatment of bacteria with antibiotics is a well-established trigger of bacterial MV formation, the underlying mechanisms are poorly understood. In this study, we show that antibiotics can induce MVs through different routes in the important human pathogen DNA-damaging agents and antibiotics inducing the SOS response triggered vesicle formation in lysogenic strains of but not in their phage-devoid counterparts. The β-lactam antibiotics flucloxacillin and ceftaroline increased vesicle formation in a prophage-independent manner by weakening the peptidoglycan layer. We present evidence that the amount of DNA associated with MVs formed by phage lysis is greater than that for MVs formed by β-lactam antibiotic-induced blebbing. The purified MVs derived from protected the bacteria from challenge with daptomycin, a membrane-targeting antibiotic, both and in whole blood. In addition, the MVs protected from killing in whole blood, indicating that antibiotic-induced MVs function as a decoy and thereby contribute to the survival of the bacterium.