Assessing antibiotic tolerance of Staphylococcus aureus derived directly from patients by the Replica Plating Tolerance Isolation System- REPTIS

Antibiotic tolerant Staphylococcus aureus pose a great challenge to clinicians as well as to microbiological laboratories and are one reason for treatment failure. Antibiotic tolerant strains survive transient antibiotic exposure despite being fully susceptible in vitro. Thus, fast and reliable methods to detect tolerance in the routine microbiology laboratory are urgently required. We therefore evaluated the feasibility of the replica plating tolerance isolation system (REPTIS) to detect antibiotic tolerance in S. aureus isolates derived directly from patients suffering from different types of infections and investigated possible connections to clinical presentations and patient characteristics. One hundred twenty-five S. aureus isolates were included. Replica plating of the original resistance testing plate was used to assess regrowth in the zones of inhibition, indicating antibiotic tolerance. Bacterial regrowth was assessed after 24 and 48 hours of incubation and an overall regrowth score (ORS) was assigned. Regrowth scores were compared to the clinical presentation. Bacterial regrowth was high for most antibiotics targeting protein synthesis and relatively low for antibiotics targeting other cellular functions such as DNA-replication, transcription and cell wall synthesis, with the exception of rifampicin. Isolates with a blaZ penicillinase had lower regrowth in penicillin and ampicillin. Low ORSs were more prevalent among isolates recovered from patients with immunosuppression or methicillin-resistant S. aureus (MRSA) isolates. In conclusion, REPTIS is useful to detect antibiotic tolerance in clinical microbiological routine diagnostics. Rapid detection of antibiotic tolerance offers a new diagnostic readout that might allow more tailored treatments in the future.