Elution, detection, and quantification of polio I, bacteriophages, Salmonella Montevideo, and Escherichia coli O157 : H7 from seeded strawberries andtomatoes

This study compared the effect of different physical and chemical treatment s of strawberries and tomatoes to determine their ability to recover seeded viral and bacterial pathogens from produce surfaces. Solutions of salts, a mino acids, complex media, and detergents were compared as eluants. Phospha te-buffered saline (PBS) containing 0.1% Tween 80 eluted the highest number of seeded microorganisms. Elution with this defined solution was then comp ared under different conditions of physical agitation. Rotary shaking for 2 0 min at 36 degreesC eluted higher numbers of viruses and bacteria than did low- or high-speed stomaching. Commercially available and laboratory prepa red bacteriological differential media were compared for their ability to r ecover and distinguish eluted Salmonella Montevideo and Escherichia coli O1 57:H7 strains from seeded produce. The recovery of seeded bacterial pathoge ns was low when differential media containing selective ingredients were us ed (MacConkey sorbitol agar, XLD agar, MacConkey agar). Highest recoveries were obtained on a medium consisting of tryptic soy agar supplemented with sodium thiosulfate and ferric ammonium citrate compared with selective medi a that inhibited up to 50% of the growth of the eluted microorganisms.