Revival of Krebs–Ringer balanced salt solution for the investigation of polymorphonuclear leukocytes and Pseudomonas aeruginosa biofilm interaction

ABSTRACT To study the interaction between aggregating bacteria and polymorphonuclear leukocytes (PMNs) in vitro, the chosen medium must favor both the isolated PMNs and the bacteria. To investigate the best-suited medium for the in vitro survival of isolated unactivated human PMNs, we compared three different mammalian cell media: Krebs–Ringer balanced salt solution (BSS), Hanks’ BSS (HBSS) and Roswell Park Memorial Institute (RPMI) 1640. The death of PMNs was estimated by the release of lactate dehydrogenase activity. Furthermore, two types of serum, human (HS) and fetal bovine (FBS), were compared at different concentrations (0%, 2%, 5%, 10%) and at three different time points (2, 4, 20 h). We show that Krebs–Ringer BSS prolonged the survival of PMNs compared to HBSS and RPMI 1640 and that the addition of 10% FBS significantly enhanced the long-term survival (20 h) compared to HS. Furthermore, we observed aggregation of Pseudomonas aeruginosa when grown in the presence of either a mixture of histones, histone H3, arginine or lysine. In this study, we show that the use of Krebs–Ringer BSS is highly relevant for the study of the interaction of bacteria and PMNs in relation to novel treatment strategies of biofilm infections due to the reproduction of bacterial aggregation as seen in chronic bacterial infections. Krebs–Ringer BSS stimulates the survival of polymorphonuclear leukocytes in vitro, and the addition of histones induces the reproduction of bacterial aggregation as seen in chronic bacterial infections.