Fosfomycin enhances phagocyte-mediated killing of Staphylococcus aureus by extracellular traps and reactive oxygen species

Abstract

The successful treatment of bacterial infections is the achievement of a synergy between the host’s immune defences and antibiotics. Here, we examined whether fosfomycin (FOM) could improve the bactericidal effect of phagocytes, and investigated the potential mechanisms. FOM enhanced the phagocytosis and extra- or intracellular killing of S. aureus by phagocytes. And FOM enhanced the extracellular killing of S. aureus in macrophage (MФ) and in neutrophils mediated by extracellular traps (ETs). ET production was related to NADPH oxidase-dependent reactive oxygen species (ROS). Additionally, FOM increased the intracellular killing of S. aureus in phagocytes, which was mediated by ROS through the oxidative burst process. Our results also showed that FOM alone induced S. aureus producing hydroxyl radicals in order to kill the bacterial cells in vitro. In a mouse peritonitis model, FOM treatment increased the bactericidal extra- and intracellular activity in vivo, and FOM strengthened ROS and ET production from peritoneal lavage fluid ex vivo. An IVIS imaging system assay further verified the observed in vivo bactericidal effect of the FOM treatment. This work may provide a deeper understanding of the role of the host’s immune defences and antibiotic interactions in microbial infections.

Macrophage Extracellular Traps: A Scoping Review

“…Wong and Jacobs [30] used the elastase inhibitor, Nmethoxysuccinyl-Ala-Ala-Pro-Val-chloromethyl ketone (AAPV), to block monocyte-derived macrophages infected with M. tuberculosis or S. aureus from releasing METs. Shen et al [40] found similar results with AAPVtreated mouse peritoneal macrophages infected with S. aureus. In contrast, Je et al [26] noted AAPV-treated THP-1 macrophage-like cells infected with M. massili ense were unaffected with regard to MET release despite elastase being identified within the MET structures.…”

“…There have been mixed results using this technique as some groups have noted decreased MET release in cells pretreated with cytochalasin D [25,26]. To date, there are reports of potential MET microbicidal activity against pathogens including Staphylococcus aureus, S. agalactiae, E. coli, and C. albicans [28,[38][39][40]. Halder et al [22] isolated monocyte ETs by digesting immobilized traps with the restriction enzyme AluI, and then added ET material to C. albicans culture; ET material, but not monocyte chromosomal DNA, was able to inhibit fungal growth even at 30 h of incubation.…”

“…They proposed that activated complement might add microbicidal activity and allow for the enhanced opsonization and phagocytosis of organisms within ETs during the resolution of inflammatory responses [22]. Shen et al [40] showed that the antibiotic fosfomycin may boost MET release, potentially by increasing ROS production, and enhance the total extracellular killing of S. aureus by mouse peritoneal macrophages producing METs.…”

“…Reports have demonstrated that inhibitors of the NADPH-oxidase system including diphenylene iodonium reduce MET formation, although this has not been consistent across all studies [23,25,28,29,40]. King et al [47] used a fluorescent readout of ROS production (dihydrorhodamine 123) to indicate that human alveolar macrophages producing METs had a 2-fold increase in ROS fluorescence compared to cells not forming METs.…”

Targeting intracellularStaphylococcus aureusto lower recurrence of orthopaedic infection

“…This concentration was used to determine the concentration for the gentamicin protection assay, in which extracellular bacteria are killed but intracellular cells are protected in eukaryotic cells, which are relatively impervious to aminoglycosides. The protected cells are then released by lysis for subsequent enumeration …”