1.normal plates select spreader-free plate. Count all colony forming units including those of pinpoint size, on selected plate. record dilutions used and total number of colonies counted.
2. plates with more than 250 colonies. When number of CFU plate exceeds 250, for all dilutions, record the counts as too numerous to count for all but the plate closest to 250, and count CFU in those portions of plate that are representative of colony distribution. See ref. 2 for detailed guidelines. Mark calculated APC with EAPC to denote that it was estimated from counts outside 25-250 per plate range
3. Spreaders. Spreading colonies are usually of 3 distinct types 1. a chain of colonies, not too distinctly separated, that appears to be caused by disintegration of a bacterial clump 2. one that develops in firm of water between agar and bottom of dish and 3 one that forms in firm of water at edge or on surface of agar. If plates prepared from sample have excessive spreader growth so that area covered by spreaders, including total area of repressed growth exceeds 25% of plate area, report plate as spreaders. When it is necessary to count plates containing spreaders not eliminated by a or b above, count each of the 3 distinct spreader types as one source. For the first type, If only one chain exists, count it as a single colony. If one or more chains appear to originate from separate sources, count each source as one colony. Do not count each individual growth in such chains as a separate colony. Type 2 and 3 usually result in distinct colonies and are counted as such. Combine the spreader count and the colony count to compute the APC.