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Title: Assessment of bacterial biofilm on stainless steel by hyperspectral fluorescence imaging

item Jun, Won
item Kim, Moon
item Millner, Patricia
item Chao, Kuanglin - Kevin Chao

Submitted to: Sensing and Instrumentation for Food Quality and Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2009
Publication Date: 1/30/2009
Citation: Jun, W., Kim, M.S., Lee, K., Millner, P.D., Chao, K. 2009. Assessment of bacterial biofilm on stainless steel by hyperspectral fluorescence imaging. Sensing and Instrumentation for Food Quality and Safety. 3(1):41-48.

Interpretive Summary: Biofilm formation in food processing environments can increase the occurrences of microbial contamination during food product processing and raise food safety and public health risks. This paper presents the evaluation of a recently developed portable hyperspectral fluorescence imaging system to detect microbial biofilm on stainless steel surfaces commonly used for the manufacture of food processing equipment. Results showed that fluorescence imaging technique can detect auto-fluorescence from the biofilms produced by E. coli O157:H7 and Salmonella on stainless steel surfaces. Thus, our system may be potentially applicable to detection, quantification, and classification of biofilms on food processing surfaces as a rapid and nondestructive method. Research presented in this investigation is useful to food scientists, microbiologists, engineers, regulatory government agencies (FSIS and FDA), and food processing industries.

Technical Abstract: Hyperspectral fluorescence imaging techniques were investigated for detection of two genera of microbial biofilms on stainless steel material which is commonly used to manufacture food processing equipment. Stainless steel coupons were deposited in nonpathogenic E. coli O157:H7 and Salmonella cultures, prepared using M9 minimal medium with casamino acids (M9C), for 6 days at 37°C. Hyperspectral fluorescence images of the biofilm formations on the stainless coupons were acquired from 416 to 700 nm with the use of ultraviolet-A (320 to 400 nm) excitation. Fluorescence images in the blue region at approximately 480 nm exhibited emission peaks for both bacteria and thus provided the highest contrast between the biofilms and the background of the stainless steel coupons. On the basis of Principal component analysis (PCA) of the hyperspectral fluorescence images, the second principal component score images exhibited clear morphological differences in biofilm formations between E. coli and Salmonella. E. coli formed granular aggregates of biofilms above the medium on stainless steel while Salmonella formed dense biofilm in the medium-air interface region (pellicle). A simple thresholding of the fluorescence image at 480 nm showed significantly higher intensity fluorescence of biofilm regions for Salmonella than for E. coli O157:H7. Viable cell counts of the samples confirmed that Salmonella was found to form more biofilm than E. coli O157:H7. Hyperspectral fluorescence imaging techniques can be used as a rapid, nondestructive method to detect and quantify biofilm formation on stainless steel, and to potentially differentiate bacteria based on spatial morphological growth patterns. It is feasible to apply fluorescence imaging techniques to rapidly screen large area food processing surfaces for bacterial contaminations.