Rapid detection and toxicity assessment of ochratoxin A by Photobacterium leiognathi in drinking water

This study was aimed to develop a rapid technique for detection of ochratoxin A (OTA) by Photobacterium leiognathi (P. leiognathi) based on its inhibition of luminescence on P. leiognathi. The freeze-dried powder of P. leiognathi was incubated and grown aerobically in sterile liquid medium at 28 °C for 20 h. Optical cell density (OD) at wavelength of 610 nm was measured using UV spectrometer every 2 h. Different concentrations of standard OTA solution were used to measure its luminescence inhibition and calculate its half maximal inhibitory concentration (IC₅₀). Scanning electron microscopy (SEM), flow cytometry (FCM), sodium dodecyl sulphonate polyacrylamide gel electrophoresis (SDS-PAGE), DNA extraction and gel electrophoresis were used to observe the performance of P. leiognathi under the treatment of OTA. A correlation (R² > 0.98) was obtained between the relative luminosity unit of P. leiognathi and OTA concentration in the range of 0.01–20 mg L⁻¹ with recoveries of 80.8–87.4%. The effects of OTA on P. leiognathi are time-dependent, and the IC₅₀ value of 12.71 mg L⁻¹ at 30 min demonstrated its good sensitivity to OTA. The cells of P. leiognathi under 40 mg L⁻¹ OTA exposure for 30 mins showed morphological alterations, protein damage, apoptosis and necrosis. The aforementioned results indicate that biological assay is a promising and alternative method used for rapidly monitoring the sudden pollution of OTA in the early emergency warning of drinking water system.