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Automated Counting of Bacterial Colony Forming Units on Agar Plates

Figure 5

Performance of the automated colony counter.

A. Performance of automated colony counting (dots) of S. pneumoniae CFUs and routine manual counting (squares) versus the gold standard of manual counting on high performance images (X-axis). A total of 22 plates of 7 different pneumococcal strains were analyzed (CFU range 16–749; mean 133.5, median 55.5). Linear regression analysis of manual and automated colony count versus the gold standard showed a significant difference of the two slopes (p<0.0001) with a slope of 1.01(SD ±0.016; 95% confidence interval (CI) 0.98–1.04) for the automated colony counter and a slope of 0.67(SD±0.03; CI 0.61–0.73) for routine manual counting (95% confidence interval is indicated with dotted lines). B. Performance of automated colony counting (dots) of S. pneumoniae CFUs on blood agar plates versus the gold standard of manual counting on high performance images (X-axis). A total of 26 plates of 7 different pneumococcal strains (CFU range 36–853; mean 176, median 101.5) were analyzed. Linear regression showed a slope of 1.02 (SD±0.01; CI 1–1.03) (95% confidence interval is indicated with dotted lines). C. Performance of automated colony counting (dots) of M. catarrhalis CFUs on BHI plates versus the gold standard of manual counting on high performance images (X-axis). 25 plates of M. catarrhalis strain 25238 were used (CFU range 20–70, mean 43.9, median 42). Linear regression analysis of automated colony count versus the gold standard showed a slope of 1 (SD ±0.008; CI 0.981–1.033) for the automated colony counter. D. Performance of automated colony counting (dots) of P. aeruginosa CFUs on blood agar plates versus the gold standard of manual counting on high performance images (X-axis). 8 plates of P. aeruginosa clinical isolate (strain 460229) were analyzed (CFU range 1–386, mean 142.3, median 37). Linear regression analysis of automated colony count versus the gold standard showed a slope of 0.89 (SD ±0.033; CI 0.81–0.97) for the automated colony counter.

Figure 5

doi: https://doi.org/10.1371/journal.pone.0033695.g005