Fig 2. Prevalence of resistance in non-type-specific E. coli recovered from feedlot cattle, by sampling date.

Marginal (adjusted) means estimates of the prevalence of resistance to various antimicrobial drugs among non-type specific E. coli isolates obtained from individual fecal samples at the first and second samplings. These estimates have been adjusted for isolate, individual, and pen effects. Due to a large variation in second sampling relative to days on feed, estimates have been categorized and presented at 33–75 days on feed, 75–120 days on feed, and >120 days on feed. Error bars represent 95% confidence intervals. Dashed lines differentiate which antimicrobial drugs were tested by one or both susceptibility testing methods. Number of isolates in legend indicate how many were tested by each susceptibility test (n = number tested by disk diffusion / number tested by both tests / number tested by broth microdilution). P-values relate to differences in adjusted prevalence among the 4 days-on-feed categories, and were not adjusted for multiple comparisons among AMDs. * = unadjusted prevalence with “plus four 95% confidence interval for a proportion".