FIG. 2.

Preharvest population dynamics of (A) E. coli O157:H7 strain H1827R and (B) Salmonella enterica serovar Thompson strain RM1987N on young (•), middle (▴), and old (▪) leaves of young romaine lettuce plants. The plants were inoculated with each pathogen separately and were then incubated at 28°C under conditions conducive to the presence of free water on the leaf surface. (C) Population sizes of the indigenous culturable bacterial flora on the leaves of plants inoculated with strain H1827. Each datum point represents the mean of the log-transformed value of the bacterial population size per gram tissue of 10 leaf samples; error bars indicate ±1 standard error of the mean.