CMS SOM App. H, Tag V256

7.2.3 Heterotrophic plate count (dip samplers)

Dip samplers may be used for bacterial surveillance… in conjunction with a quality

assurance program designed to ensure their appropriate use. Elements of the quality

assurance program should include staff training in areas such as the correct methods of

inoculation, incubation, and interpretation, and verification involving duplicate samples

sent to a certified laboratory on at least an annual basis. Plates shall be incubated at 35 °C

for 48 hours.

Colonies should be counted using a magnifying device.

Interpretive Guidance § 494.40(a)

ANSI/AAMI RD52:2004

7.2.3 Heterotrophic plate count

This method is an indicator of water quality only and is not to be confused with total

heterotrophic plate counts, which require much longer incubation times at 28° C.

If a more accurate count from plates containing fewer than 30 or more than 300 colonies is

desired, larger or smaller volumes may be cultured. Smaller volumes can be obtained by making

1:10 serial dilutions in sterile phosphate buffer. If larger volumes are required, the membrane

filtration method should generally be used.

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Erratic colony counts . . . may indicate the presence of biofilm since sloughing of biofilm may

occur with release of bacteria into the water. [W]hen contamination persists in spite of frequent

and aggressive disinfection, it may be necessary to determine if biofilm is present in the system.

Additional Guidance:

Facilities that use dip samplers must send duplicate samples to a laboratory at least annually to

evaluate the accuracy of the testing done with the dip samplers.