BACTOSCAN-8000 - RESULTS OF AN INTERLABORATORY STUDY

The fluorescent microscopic counting of single bacteria in milk (Bacto scan 8000) is applied as a routine method for the determination of the bacteriological quality of ex-farm milk in an increasing number of co untries. The working group ''Bacterial count in milk - Bactoscan metho d'' of the ''Commission in Charge of Article 35 of the German Food Act s'' has examined this method in an interlaboratory study to establish the precision characteristics repeatability (r) and reproducibility (R ). In the interlaboratory study 10 samples (n = 8 raw milk, n = 2 cali bration milk), which were divided into 4 subsamples and coded at rando m, were counted (each subsample 4 times) in 13 experienced labs. The p recision data proved to be dependent on the counting level and on the milk sample. For 3 different counting levels the following data (in lo g Bactoscan counts (BCs)) for repeatability (r) and reproducibility (R ), respectively, were evaluated: level log 1.6 BC (= lin 40 BC): 0.183 and 0.247; level log 2.0 BC (= lin 100 BC): 0.111 and 0.182; level lo g 2.4 BC (= lin 250 BC): 0.109 and 0.152. Compared to the precision da ta indicated for the macrocolony reference method in colony forming un its (mean r = log 0.20 cfu/ml and R = log 0.32 cfu/ml) the repeatabili ty (r) of the Bactoscan method resembles or surpasses that of the refe rence method at higher counting levels (greater than or equal to 30 BC ), and the reproducibility (R) of the Bactoscan method was similar (n = 2 milk samples) or markedly superior (n = 6 milk samples).