Figure 1. Total culturable aerobic bacterial population sizes on Romaine lettuce during field trials in 2009 and 2010 after inoculation of E. coli O157:H7.

Culturable bacteria were enumerated on TSA starting at the time of E. coli O157:H7 inoculation approximately 1 week after thinning and 4 weeks prior to plant maturity. Overhead irrigated (○) and drip irrigated (●) plants were inoculated with E. coli O157:H7 (n=12) (solid lines) or non-inoculated controls (dashed lines). Each point represents the average ± the standard error. hpi: hours post inoculation of E. coli O157:H7; dpi: days post inoculation of E. coli O157:H7; n=12; *n=3 control plants.