99D-4 |
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J. -H. RYU, H. Kim, and L. R. Beuchat. Center for Food Safety, Dept. of Food Science & Technology, Univ. of Georgia, 1109 Experiment St., Griffin, GA 30223-1797 The effects of nutrient availability and temperature on attachment and biofilm formation by Escherichia coli O157:H7 strain 43895-EPS, which produces exopolysaccharides (EPS), and strain 43895 (not an EPS producer) on stainless steel coupons (SSC) were investigated. Cells grown on lettuce juice agar (LJA) at 22°C for 72 h were suspended in phosphate-buffered saline (PBS, pH 7.2). SSC were immersed in the cell suspension (108 cfu/ml), incubated at 4°C for 24 h, rinsed, and vortexed in PBS with glass beads. The number of attached cells was determined by plating suspensions on tryptic soy agar (TSA). Biofilm formation in 10% tryptic soy broth (TSB), lettuce juice broth (LJB), and minimal salts broth (MSB) was determined. SSC on which cells had attached were rinsed, immersed in TSB (10%), LJB, and MSB, and incubated at 12 and 22°ÆC for up to 6 days. SSC were then rinsed and cfu/coupon was determined. A significantly lower number (4.9 log10 cfu/coupon) of strain 43895-EPS, compared to strain 43895 (6.6 log10 cfu/coupon), attached on SSC. Neither strain formed biofilm on SSC immersed in TSB (10%) or LJB, regardless of incubation temperature. The population on SSC decreased during the first day of incubation, then increased between day 1 and day 2 and remained constant for 6 days, but did not reach the initial population of attached cells. Both strains formed biofilms in MSB at 12 and 22°C. Populations of strains 43895 and 43895-EPS were 8.4 and 7.1 log10 cfu/coupon, respectively, after 2 days at 22°C and 8.2 and 6.6 log10 cfu/coupon, respectively, after 6 days at 12°C. It is concluded that EPS production by E. coli O157:H7 inhibits attachment on SSC and reduced nutrient availability enhances biofilm formation. However, in a given nutrient medium, EPS production and reduced incubation temperature did not markedly affect biofilm formation.
Session 99D, Food Microbiology: General
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