Resistance of veillonella to hydrosoluble pristinamycins: a possible outer membrane barrier effect

An in vitro study on 25 Veillonella strains showed a consistent clindamycin susceptibility with resistance to erythromycin and to the hydrosoluble pristinamycins, quinupristin and dalfopristin and its 30:70 combination, the synergistin RP59500. Double erythromycin-clindamycin disk tests did not show any inducible resistance pattern. The addition of 10 or 50 mug/mL of polymyxin B nonapeptide, an outer membrane permeabilizing agent, consistently reduced quinupristin and dalfopristin MICs in most strains. This result suggests that the Veillonella outer membrane may act as a permeability barrier to these antibiotics, as in the case of other Gram-negative bacteria.