A Waveguide Resonator Sensor for Bacterial Growth Monitoring: Towards Antibiotic Susceptibility Testing

In the current landscape of inappropriate antibiotic use leading to antimicrobial resistance, research on Bacterial Growth Monitoring (BGM) and Antibiotic Susceptibility Testing (AST) methods has gained major importance. This paper proposes a waveguide resonator biosensor for real-time and non-contact BGM with future application in AST. The sensor operated based on creating a resonant section sandwiched between two inductive irises. The resonant section consisted of an opening through which the bacterial sample in the test tube in placed, creating material perturbations. Bacteria growth caused alterations in the complex permittivity of the resonant section, changing the resonant characteristics that were monitored in the reflection coefficient of the waveguide. Experimental results indicated a ~6.7 dB increase in the magnitude of the reflection coefficient for the growth of 50 µL of E. coli in 5 mL of Luria-Bertani (LB) broth at 37°C, over a period of 12 hours. To evaluate the capability for AST, investigations were extended to monitor the bacterial growth trends in the presence of different antibiotic concentrations in the media. The observed trends in the S11 data demonstrated a relationship between bacterial growth rates and concentrations of antibiotics (in the growth media), promising the potential of the proposed sensor as an effective AST method.