Heterotrophic Bacteria & Water Potability

PART 1 – Introduction
By Christian Panganiban, Microbiology Lab Coordinator

Bacteria can be classified as either autotrophic or heterotrophic depending on their ability to assimilate carbon-containing compounds from the environment. Autotrophic bacteria obtain carbon from inorganic sources, such as CO2. Heterotrophic bacteria (HB) require organic carbon sources, such as carbohydrates and proteins. Most bacteria are heterotrophic, including those known to be pathogenic to humans.

HB are found throughout the environment, including water. Their unique ability to adapt to the nutrient–poor environment of water systems allows HB to thrive in comparison to other organisms such as coliforms, which require more complex environmental conditions to proliferate. As such, testing for HB is an important component of any thorough analysis of a water system.

The concentration of HB in the water system is important to know for a couple of reasons. First, it is an indicator of the efficacy of water treatment. If a treatment is working properly, the post-treatment concentration of HB will be lower than the pre-treatment level of HB.

Secondly, HB interferes with the ability to detect coliforms, a common bacterial indicator for fecal contamination. As stated earlier, HB adapt to the nutrient-deficient environment of the water system. Consequently, coliforms are overwhelmed at high concentrations of HB. At approximately 500 CFU per mL or greater, detection of coliforms is compromised greatly. Without a reliable coliform detection system in place, water systems become susceptible to fecal contamination and exposure to pathogenic organisms such as E. coli, Campylobacter, and enteric viruses.

Part 2 of this series will explore the methodology employed by various laboratories in analyzing HB in solid and liquid matrices, the mechanism of HB interference and limitations of HB analyses.