Inactivation effect of low-energy X-ray irradiation against planktonic and biofilm Pseudomonas fluorescens and its antibacterial mechanism.

Pseudomonas fluorescens is a well-known biofilm former on food contact surfaces and can cause severe cross-contamination in food processing premises. This study aimed to determine the inactivation effect of low-energy X-ray on P. fluorescens planktonic cells in phosphate-buffered saline solution (PBS) and P. fluorescens biofilm cells on food-contact-surface (stainless steel). The results demonstrated that low-energy X-ray irradiation at 125 Gy inactivated 4.60 log CFU/mL and 4.21 log CFU/cm2 for P. fluorescens planktonic and biofilm cells, respectively. Based on Weibull model, low-energy X-ray achieved tR1 values of 14.8 Gy and 11.6 Gy for P. fluorescens planktonic and biofilm cells, respectively. Apart from cell inactivation, the irradiation also led to the destruction of extracellular polymeric substances (EPS) structure. Low-energy X-ray irradiation markedly damaged bacterial glucose uptake system and resulted in part loss of bacterial membrane potential and integrity. These results suggested the potential of the low-energy X-ray for inactivating P. fluorescens biofilm cells and removing EPS in food industry.

Low-energy X-ray inactivation of Listeria monocytogenes in mono-/co-culture biofilms with Pseudomonas fluorescens on food contact surfaces.

This study assessed the inactivation kinetics of 150 keV low-energy X-ray on mono-/co-culture biofilms of Listeria monocytogenes and Pseudomonas fluorescens on three different food-contact-surfaces (polyethylene, acrylic, and stainless steel). The results indicated that the level of biofilm formation of mono-/co-cultures of L. monocytogenes and P. fluorescens was the highest on acrylic. The mono-culture L. monocytogenes biofilm cells exhibited higher resistance to the low-energy X-rays than the corresponding mono-culture P. fluorescens biofilm cells, regardless of surface types. Furthermore, co-culture had enhanced the resistance of both P. fluorescens and L. monocytogenes biofilm cells to the low-energy X-ray. Two kinetic models for the inactivation process were investigated, including (i) Linear model and (ii) Weibull model. Based on R2, RMSE and AIC analysis, the Weibull model was superior in fitting the inactivation curves of low-energy X-ray on L. monocytogenes in mono-/co-culture biofilms with P. fluorescens. For mono-culture biofilms, the irradiation achieved the tR1 value (derived from the Weibull model, i.e., the dose required for the first 1-log reduction) of 46.36-50.81 Gy for L. monocytogenes and the tR1 value of 25.61-31.33 Gy for P. fluorescens. For co-culture biofilms, higher tR1 values for L. monocytogenes (59.54-70.77 Gy) and P. fluorescens (32.73-45.13 Gy) were yielded than those for their individual counterparts in mono-culture biofilm.

Autocorrelation noise removal for optical coherence tomography by sparse filter design.

We present a reconstruction method to eliminate the autocorrelation noise (ACN) in optical coherence tomography (OCT). In this method, the optical fields scattered from the sample features are regarded as the response of a sparse finite impulse response (FIR) filter. Then the OCT reconstruction is formulated as one of identifying the parameters of a sparse FIR filter, which are obtained via an [script-l](1) optimization with soft thresholding. The experimental results show that the proposed method can obtain OCT reconstruction results with effective attenuation of ACN.

Optical coherence tomography by using frequency measurements in wavelength domain.

Optical coherence tomography (OCT) reconstruction by using frequency measurements in the wavelength domain is presented in this paper. The method directly recovers the axial scan by formulating the frequency domain OCT (FD-OCT) into an algebraic reconstruction problem. In this way, the need for interpolation is removed. Then by solving the problem with ℓ1 optimization, the computational load is significantly reduced. It is demonstrated by experiment and simulation that the proposed method can achieve high resolution and longer imaging depth compared to the FD-OCT method.