Heterotrophic plate count
Heterotrophs are broadly defined as microorganisms that require organic carbon
for growth. They include bacteria, yeasts and moulds. A variety of simple
culture-based tests that are intended to recover a wide range of microorganisms
from water are collectively referred to as “heterotrophic plate count” or “HPC
test” procedures. Accordingly, the terms “heterotroph” and “HPC” are not
synonymous.
There is no universal “HPC measurement.” Although standardized methods
have been formalized, HPC test methods involve a wide variety of test
conditions that lead to a wide range of quantitative and qualitative results.
Temperatures employed range from around 20 °C to 40 °C, incubation times
from a few hours to seven days or a few weeks, and nutrient conditions from
low to high. The test itself does not specify the organisms that are detected.
Only a small proportion of the metabolically active microorganisms present
in a water sample may grow and be detected under any given set of HPC test
conditions, and the population recovered will differ significantly according to
the method used. The actual organisms recovered in HPC testing can also vary
widely between locations, between seasons and between consecutive samples at
a single location.
Microorganisms recovered through HPC tests generally include those that are
part of the natural (typically non-hazardous) microbiota of water; in some
instances, they may also include organisms derived from diverse pollutant
sources.
Heterotrophic plate count Heterotrophs are broadly defined as microorganisms that require organic carbon for growth. They include bacteria, yeasts and moulds. A variety of simple culture-based tests that are intended to recover a wide range of microorganisms from water are collectively referred to as “heterotrophic plate count” or “HPC test” procedures. Accordingly, the terms “heterotroph” and “HPC” are not synonymous. There is no universal “HPC measurement.” Although standardized methods have been formalized, HPC test methods involve a wide variety of test conditions that lead to a wide range of quantitative and qualitative results. Temperatures employed range from around 20 °C to 40 °C, incubation times from a few hours to seven days or a few weeks, and nutrient conditions from low to high. The test itself does not specify the organisms that are detected. Only a small proportion of the metabolically active microorganisms present in a water sample may grow and be detected under any given set of HPC test conditions, and the population recovered will differ significantly according to the method used. The actual organisms recovered in HPC testing can also vary widely between locations, between seasons and between consecutive samples at a single location. Microorganisms recovered through HPC tests generally include those that are part of the natural (typically non-hazardous) microbiota of water; in some instances, they may also include organisms derived from diverse pollutant sources.
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