Detection of bacterial biofilm on stainless steel by hyperspectral fluorescence imaging

In this study, hyperspectral fluorescence imaging techniques were investigated for detection of microbial biofilm on stainless steel plates typically used to manufacture food processing equipment. Stainless steel coupons were immersed in bacterium cultures of nonpathogenic E. coli, Pseudomonas pertucinogena, Erwinia chrysanthemi, and Listeria innocua. Following a 1-week growth in rich medium tryptic soy broth (TSB) and M9 minimal medium with casamino acids (M9C), biofilm formations were evaluated using a recently developed portable hyperspectral fluorescence imaging system. Hyperspectral fluorescence images of the biofilm samples, in response to ultraviolet-A (320 to 400 nm) excitation, were acquired from 416 to 700 nm. Fluorescence images in the blue emission peak region exhibited the most contrast between biofilms and stainless steel coupons. On the basis of correlation analyses, two-band ratios compared with the single-band images enhanced the contrast between the biofilm forming area and untreated coupon surfaces. A two-band fluorescence ratio image, 444/588 nm, resulted in the greatest contrast between the biofilm formations and stainless steel coupon for the biofilms grown in M9C medium. TSB medium showed relatively high auto-fluorescence, and thus further investigation is needed to mitigate the contribution of strong TSB auto-fluorescence in detection of biofilms.