Submitted to: Association Official Analytical Chemists Annual Intrl Meeting & Exposition
Publication Type: Proceedings
Publication Acceptance Date: 10/11/2007
Publication Date: 11/28/2007
Citation: Arnold, J.W. 2007. Comparison of measurement methods for Listeria monocytogenes biofilms under flow conditions. Proceedings Presentation #78, p. 2. Interpretive Summary:
Technical Abstract: The bacterial pathogen, Listeria monocytogenes, causes a high death rate among its victims and many food product recalls. Our goal was to develop methods to quantitatively assess the pathogen under conditions that mimic food environments. Stainless steel and glass coupons were incubated in aqueous media containing minimal nutrients and exposed to bacteria under static temperature and humidity conditions. Samples were measured separately for each coupon by aerobic plate counts, a modified crystal violet assay (CV), and spectrophotometry. The mean of the log10 density (cfu/cm2) was 5.90, and the std dev ranged from 0.127 to 0.438 on 24 coupons. The CV assay resulted in different t groupings from the cell density. The mean was 0.50, and the error % was 0.595. The typical sequence of biofilm development, followed on glass coupons, exhibited a change from dispersed single cells to an all-over pattern of clumps with few dispersed. Bacterial counts from planktonic cultures at 24, 48, 72, and 144 h confirmed that L. monocytogenes remained viable throughout the experiment. The cell density log10/ml was 8.01, 8.03, 7.69, and 6.66, respectively. L. monocytogenes formed biofilms on all of the substrata tested. The variability for the CV assay was somewhat high, with std dev ranging from 0.156 to 0.394. The data will be used to grow stable biofilms of Listeria spp. for further study. This is the first use of the crystal violet assay for measurement of bacterial biofilms on stainless steel. The methods tested are applicable to other bacteria and substrata.