Three-Dimensional In Vitro Staphylococcus aureus Abscess Communities Display Antibiotic Tolerance and Protection from Neutrophil Clearance

• Published in: Infection and immunity Vol. 88; no. 11
• Main Authors: Hofstee, Marloes I, Riool, Martijn, Terjajevs, Igors, Thompson, Keith, Stoddart, Martin J, Richards, R Geoff, Zaat, Sebastian A J, Moriarty, T Fintan
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 19-10-2020
• Subjects: Abscess - immunology; Abscess - microbiology; Bacterial Infections; Drug Resistance, Microbial - physiology; Humans; In Vitro Techniques; Neutrophils - immunology; Staphylococcal Infections - immunology; Staphylococcus aureus - physiology; in vitro model; staphylococcal abscess communities; antibiotic tolerance; bacterium-host cell interactions; 3-dimensional; Staphylococcus aureus; fibrin pseudocapsule
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.00293-20

is a prominent human pathogen in bone and soft-tissue infections. Pathophysiology involves abscess formation, which consists of central staphylococcal abscess communities (SACs), surrounded by a fibrin pseudocapsule and infiltrating immune cells. Protection against the ingress of immune cells such as neutrophils, or tolerance to antibiotics, remains largely unknown for SACs and is limited by the lack of availability of
models. We describe a three-dimensional
model of SACs grown in a human plasma-supplemented collagen gel. The
SACs reached their maximum size by 24 h and elaborated a fibrin pseudocapsule, as confirmed by electron and immunofluorescence microscopy. The
SACs tolerated 100× the MIC of gentamicin alone and in combination with rifampin, while planktonic controls and mechanically dispersed SACs were efficiently killed. To simulate a host response, SACs were exposed to differentiated PLB-985 neutrophil-like (dPLB) cells and to primary human neutrophils at an early stage of SAC formation or after maturation at 24 h. Both cell types were unable to clear mature
SACs, but dPLB cells prevented SAC growth upon early exposure before pseudocapsule maturation. Neutrophil exposure after plasmin pretreatment of the SACs resulted in a significant decrease in the number of bacteria within the SACs. The
SAC model mimics key
features, offers a new tool to study host-pathogen interactions and drug efficacy assessment, and has revealed the functionality of the
pseudocapsule in protecting the bacteria from host phagocytic responses and antibiotics.