Figure 4: Quantitative analysis of depth of invasion. Depth of invasion was analyzed as described in Methods. All three PEGs and all three bacterial strains independently increased depth of invasion. A decrease in invasion was noted when samples were treated with PEG 3350 and either 261 or EPEC. Treatment with any bacterial strain and either PEG 8000 or PEG 20,000 led to increased invasion. The greatest increase was seen when samples were treated with PEG 8000 and HS4. Standard Student’s t-test was applied to the samples and the were obtained for samples treated with PEG 8000 and HS4 indicated by an asterisk (*).