International Journal of Food Microbiology 40 (1998) 57–64 An interlaboratory study to find an alternative to the MPN technique for enumerating Escherichia coli in shellfish a, b c b d * I.D. Ogden , G.C. Brown , Susan Gallacher , P.H. Garthwaite , M. Gennari , e f g a M. Pilar Gonzalez , L.B. Jørgensen , B.T. Lunestad , Marion MacRae , h i j k M. Celeste Nunes , A.C. Petersen , J.T. Rosnes , J. Vliegenthart a Department of Medical Microbiology, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, UK b Department of Mathematical Sciences, University of Aberdeen, Aberdeen, AB24 3QY, UK c Marine Laboratory, SOAEFD, Victoria Road, Aberdeen, AB11 9DB, UK d Instituto di Ispezione delgi Alimenti di Origine Animale, Sez. 1, Via Celoria 10, 20133 Milan, Italy e Instituto de Investigacions Marinas, r / Eduardo Cabello, 6. Vigo-36208, Spain f MAF, Danish Institute of Fisheries Research, DK-2800 Lyngby, Denmark g Central Laboratory, Directorate of Fisheries, Strandgaten 229, 5002 Bergen, Norway h ˆ ˜ Instituto Portugues de Investigac ¸ao Maritima, Avenue de Brasilia, 1400 Lisboa, Portugal i Cork Regional Technical College, Rossa Avenue, Bishopstown, Cork, Ireland j Norconserv, Institute of Fish Processing and Preservation Technology, PO Box 327, N-4001, Stavanger, Norway k Inspectie Gezondheidsbescherming, Evertsenstraat 17, 4461 XN Goes, Netherlands Received 9 June 1997; received in revised form 8 December 1997; accepted 28 December 1997 Abstract Nine laboratories in eight countries tested 16 batches of common mussels ( Mytilus edulis) over a 32 week period in order to find an alternative to the Most Probable Number (MPN) technique to enumerate E. coli. The alternatives investigated included the 3M Petrifilm system, the Merck Chromocult agar method and a Malthus conductance technique. The Petrifilm was found to be unsuitable and was subsequently dropped from the trial. After 669 analyses, a correlation of 0.83 was observed for log E. coli counts between the MPN and Chromocult methods and there was no significant evidence that either method tended to give higher readings than the other. The MPN was slightly better than the Chromocult method for repeatability but the Chromocult was slightly better for reproducibility. However, the observed differences are probably too small to be of practical importance. On the basis of these data therefore, the two methods appear equally suitable for E. coli enumeration in shellfish. There were poor correlations between these methods and the Malthus technique. A small but significant number of samples tested positive on the Malthus instrument but were recorded negative on the MPN and Chromocult tests. Subsequent analysis positively identified E. coli from these Malthus assays. After statistical analysis, errors were noted in both the MPN and Chromocult methods but it was found that there would be no statistical differences if the Chromocult agar were used as an alternative to the MPN technique. Published by Elsevier Science B.V. Keywords: Interlaboratory study; Escherichia coli ; MPN; Chromogenic media; Conductance; Shellfish * Corresponding author. 0168-1605 / 98 / $19.00 Published by Elsevier Science B.V. All rights reserved. PII S0168-1605(98)00016-6