Comparison of dilution schemes for enumerating fungi in ground pepper: a collaborative study.

ABSTRACT

Ten lots of ground pepper were analyzed for fungal populations using 15 and 110 dilutions in sterile 0.1% peptone. Duplicate samples (0.1 ml) diluted 15 were surface plated on dichloran rose bengal chloramphenicol (DRBC) agar whereas quadruplicate samples (0.1 ml) diluted 110 were surface plated on DRBC agar. Nine collaborators from six countries participated in the study. Significantly (p < 0.05) higher fungal populations were detected in 7 of the 10 lots of pepper diluted using the 15 dilution scheme; the other three showed no significant difference. Using 15 and 110 dilution schemes, among-laboratory variability in mean fungal populations detected was not significant (p < 0.05) for 7 of 10 and 2 of 10 lots of peppers, respectively. Coefficients of variation for reproducibility (among-laboratory variation) were 2.8% and 6.2%, respectively, using 15 and 110 dilution schemes. Analysis of collapsed data from all ten lots of pepper revealed that significantly higher populations of fungi were detected using a 15 dilution scheme.