The in vitro activity of sulphones alone and in combination with ampicillin or amoxicillin against Legionella pneumophila and other Legionella spp. including beta-lactamase studies.

Penicillinate sulphone beta-lactamase inhibitors, sulbactam, and BL-P2013, were very effective alone and in combination with ampicillin-like penicillins against 34 strains of Legionellae. The minimum concentrations inhibiting 50% of tested isolates (MIC50) results were as follows: sulbactam, BL-P2013, and amoxicillin = 2.0 micrograms/ml; ampicillin = 1.0 microgram/ml; erythromycin = 0.5 microgram/ml; and rifampin = 0.03 microgram/ml. Synergy was commonly observed when the sulphones were combined with ampicillin or amoxicillin, generally reducing the drug minimum inhibitory concentrations (MICs) fourfold to eightfold (synergy rates 85-91%). BL-P2013 was a slightly more active inhibitor of Legionella spp. beta-lactamase than dicloxacillin or sulbactam.