Fecal coliform methods for examination of sea water: interlaboratory evaluation of split sample analysis

An interlaboratory study was conducted to compare the effectiveness of the following 3 multiple-tube fermentation methods for determining the most probable number (MPN) of Escherichia coli in a split artificial sea water sample: (1) the 72-hr standard methods procedure of the American Public Health Association, (2) a 24-hr elevated-temperature test using A-1 medium, and (3) a 24-hr elevated temperature test modified to include an initial 3-hr resuscitation period using A-1 medium. The capability of the laboratories to perform the 3 test procedures was also compared. Split sample replicates with low, medium, and high levels of E. coli were examined in 18 laboratories in the United States and Canada. Data indicate that the laboratories performed each test with equal capability, and all 3 procedures were equally effective in enumerating the strain of E. coli used in this investigation. By virtue of its homogeneity and stability, the split sample served as an appropriate specimen for this study and could probably be used as a proficiency test specimen for evaluating laboratory analyst performance in the bacteriological examination of sea water.