Attachment and Biofilm Formation by Selected Strains of Salmonella enterica and Entrohemorrhagic Escherichia coli of Fresh Produce Origin

This study compared the abilities of selected Salmonella enterica and enterohemorrhagic Escherichia coli (EHEC) strains of fresh produce origin to form biofilms on polystyrene surface and to attach to alfalfa and bean sprouts. Each of the 7 S. enterica and 4 EHEC inocula (2 mL; 10(7) CFU/mL) was placed in 6 different broths in 24-well polystyrene tissue culture plates at 28 degrees C for 1 to 7 d. Developed biofilms were quantified using the crystal violet binding assay. In a separate experiment, alfalfa and mung bean sprouts (5 g) were exposed to 25 mL inocula (10(7) CFU/mL) of S. enterica or EHEC at 22 degrees C for 2 h with shaking at 40 rpm. Contaminated sprouts were thoroughly rinsed and homogenized in 0.1% peptone water, and bacteria attached to sprouts were enumerated. Biofilm mass accumulated on polystyrene surface increased with incubation time (P < 0.05). Among the microbiological media used, LB no salt (NaCl) broth better supported biofilm development (P < 0.05). Two EHEC strains formed more biofilms than the Salmonella and other two EHEC strains (P < 0.05). However, more Salmonella cells (5.66 log CFU/g) attached to sprouts than EHEC cells (3.46 log CFU/g). Both Salmonella and EHEC attached in higher numbers to mung bean, than alfalfa, sprouts (P < 0.05). Practical Application This study determined the ability of some strains of S. enterica and enterohemorrhagic E. coli (EHEC) strains of fresh produce origin to form biofilm on polystyrene surface and their ability to attach to alfalfa and bean sprouts. Information obtained from the research deepens our knowledge on the interaction of selected bacterial pathogens with their contact surfaces and fills the knowledge gap in the current body of literature.