Intracellular activity of antibiotics against a stable small colony variant of Staphylococcus aureus isolated from a CF patient in model Calu-3 human airway epithelial cells

Abstract number: P1058

Nguyen H.A., Denis O., Vergison A., Tulkens P.M., Struelens M.J., Van Bambeke F.

Objectives: Persistence of S. aureus infections in CF may be related to the presence of small colony variant (SCV) variants and of intracellular bacteria. Using a stable thymidine-auxotrophic mecA negative SCV of S. aureus isolated from a CF patient, we showed that most antibiotics (AB) act only poorly on intracellular forms in a model of human THP-1 macrophages (ICAAC 2007, abstr. A1437). We have now compared the activity of commonly used (gentamicin, rifampicin, vancomycin, moxifloxacin) and newly developed AB (linezolid, tigecycline, oritavancin) against this SCV isolate using Calu-3 cells as a model of airway epithelium.

Methods: MICs were determined in MH broth after 48 h incubation. Intracellular activities (IA) were measured as the change in post-phagocytosis inoculum [delta log CFU] after 24 h or 96 h in Calu-3 cells (normal bronchial epithelial cells) incubated with ABs at extracellular concentrations (Ce) corresponding to their respective peak (Cmax), free peak (fCmax), trough (Cmin) and free trough (fCmin) in plasma when administered at standard doses.

Results: Over 24 h, the intracellular inoculum remained constant (-0.14 ± 0.01 log CFU with 10 mg/L lysostaphin to prevent extracellular growth). All AB showed a concentration-dependent effect, with a significant inoculum decrease at Cmax for TGC, LNZ and RIF, fCmax for MXF, Cmin for ORI low dose, and fCmin for GEN, VAN and ORI high dose. At 96 h, the activity of all drugs (except LNZ and TGC) markedly progressed at Cmax, approaching or reaching a bactericidal effect, while regrowth was observed at Cmin for all drugs but VAN, MXF and RIF.

Conclusion: Prolonged incubation with high concentrations of bactericidal drugs is needed to durably act on intracellular SCVs, suggesting the importance of AB selection and PK/PD optimisation to avoid failure in eradicating these bacteria in CF patients.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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