Reproducibility of Automated and Manual Counting of VSC Producing Organisms

D. Ricci-Nittel, D.S. Harper, K.A. Baxter, and M.W.B. Araujo, (Pfizer Consumer Healthcare, Morris Plains, NJ USA, Hill Top Research Inc, Miamiville, OH, USA). Poster # 1034 presented at AADR 2006 (Orlando, FL, March 2006).

ABSTRACT

Objective: To determine intra- and inter-examiner reproducibility of manual and automated counting of volatile sulfur compound (VSC) producing colonies on OOPS III media (Turng et al., 1997). Methods: Human saliva was collected from donors known to have salivary populations of VSC-producing microorganisms, pooled, diluted, and plated on pre-reduced OOPs III medium (20 plates from the common inoculum). Plates were incubated anaerobically to permit growth of dark (VSC-producing) colony forming units (CFUs), and then counted by four trained operators. Plates were counted twice in random order by both manual and automated (ProtoCOL RGB Synbiosis) methods. Plate counts were used to calculate CFU/mL values and Log10 transformed prior to statistical analysis. Standard error of the measurement (SE) was calculated (Araujo et al, 2003). Data analysis included determination of SE for intra- and inter-examiner with both techniques. In addition, the inter-method reproducibility was evaluated to determine whether or not the manual method is a valid alternative to the use of the machine. Results: Based on log10 CFU/mL, the mean ± standard deviation (SD) intra-examiner SE was 0.07 ± 0.01 for the automated instrument, and 0.04 ± 0.02 for the manual count. The mean ± SD inter-examiner SE was 0.08 ± 0.01 for the automated method and 0.05± 0.01 for manual. When calculating the inter-method SE, results showed a mean ± SD of 0.09 ± 0.01 for all 4 operators. Conclusions: The determination of the SE provides an easy method to measure operator reproducibility when reading plates by manual or automated methods. The reproducibility calculations demonstrated that the examiners are calibrated in all aspects of intra- and inter-reproducibility. Finally, the present study showed that manual or automated techniques produce comparable counts of VSC microorganisms grown on OOPs III agar plates; therefore, either method may be used in research settings.