Effects of Preparation and Storage of Agar Media on the Sensitivity of Bacterial Forward Scattering Patterns

Abstract

Recent worldwide foodborne outbreaks emphasize the need for the development of rapid and accurate method for pathogen detection. To address such issues, a new colony based label-free detection method working on the principles of elastic light scattering was introduced. In order to build libraries of scattering images for bacterial pathogens, it is pertinent to determine the effect of preparation and storage of the agar media on the scatter patterns. Scatter patterns of three Escherichia coli serovars (O26, O111 and O157) were studied and used in a model system, after growth on Sorbitol-MacConkey agar plates that were prepared and stored at different conditions in the laboratory. Quantitative image processing software was used to analyze variation in scatter patterns of the same serovar on media prepared under various standard laboratory conditions and to generate a cross-validation matrix for comparison. Based on the results, it was determined that attention should be given during preparation of media so that the agar plates are not air-dried more than 10 -20 min after solidification at room temperature. The plates could be stored in sealed bags in cold room (4˚C -10˚C) for up to a month before use. The findings of this study should provide guidelines in preparation, storage, and handling of media for generation of reproducible scatter patterns of bacterial colonies with the light scattering sensor for pathogen detection.

Laser-induced speckle scatter patterns in Bacillus colonies

“…As the modeling of forward scattering pattern for the bacteria colony shows, the morphology and optical characteristics play major roles into formation of diffraction patterns. Previous studies have shown that availability of nutrients and agar concentration (Bae et al, 2011 ), and storage condition of the agar plate (Mialon et al, 2012 ) possibly affect the distribution/propagation of cells within a colony and the resulting diffraction pattern. Furthermore, previous studies (Bae et al, 2007 , 2010 ; Kim et al, 2013 ) indicate that the forward scattering patterns produced by BARDOT are circular symmetric or concentric circle with some radial spokes for most of the microorganisms ( E. coli , Listeria , Salmonella , and Staphylococcus ) studied.…”

Light Scattering Sensor for Direct Identification of Colonies of Escherichia coli Serogroups O26, O45, O103, O111, O121, O145 and O157

“…The media included: BHI agar, Sorbitol MacConkey (SMAC; Becton Dickinson) agar, Rainbow Agar O157 (Biolog, Hayward, CA), BBL CHROMagar O157 (Becton Dickinson), and R&F E. coli O157:H7 medium (R&F Products, Downers Grove, IL). Agar plates were prepared as instructed by the manufacturer, tempered to 45°C, dispensed 20 mL/plate, cooled at room temperature for 10–20 min, and stored in a sealed plastic bag until use (used within 7–30 days) [54] . After plating appropriate dilutions of bacterial cultures, the plates were incubated at 37°C for 10–12 h or until the colony size reached 1.1±0.1 mm in diameter.…”

Exploring Bacterial Colonies in Solid Foods or Model Foods Using Non-Destructive Techniques

“…As the modeling of forward scattering pattern for the bacteria colony shows, the morphology and optical characteristics play major roles into formation of diffraction patterns. Previous studies have shown that availability of nutrients and agar concentration (Bae et al, 2011), and storage condition of the agar plate (Mialon et al, 2012) possibly affect the distribution/propagation of cells within a colony and the resulting diffraction pattern. Furthermore, previous studies (Bae et al, 2007Kim et al, 2013) indicate that the forward scattering patterns produced by BARDOT are circular symmetric or concentric circle with some radial spokes for most of the microorganisms (E. coli, Listeria, Salmonella, and Staphylococcus) studied.…”