Presence/Absence Tests for Total Coliform

Public and environmental health protection requires safe drinking water, which means it must be free of pathogenic bacteria. Among the pathogens transmitted in water sources, enteric pathogens are the most frequently encountered. Therefore, sources of fecal contamination in waters dedicated to human activities must be strictly controlled. Microbial water quality testing is an important component of water safety management, and screening for fecal contamination through microbial water quality monitoring is an important component of safe drinking water supplies and public health protection. Since coliforms (total coliforms) is one of the most important fecal indicators, concerns about improving the monitoring of drinking water hygiene quality have prompted interest in detecting total coliforms. The presence/absence test measures the concentration of all coliforms in a water sample, with higher concentrations being associated with the possible presence of disease-causing organisms.

Presence/absence testing has been used as a simpler and equally sensitive measurement of potential fecal contamination in large municipal chlorinated water systems. BOC Sciences has designed a simplified presence/absence qualitative test, in which colorimetric titration method is applied, to detect coliforms in drinking water.

Figure 1. Total & Fecal Coliform

• What is total coliforms?

Coliforms are the natural component of the microorganisms of the intestinal tract of warm blooded mammals, including humans. Coliforms bacteria can be found in surface water, groundwater, soil, vegetation, insect feces, and in the feces of warm blooded animals. Total coliforms are easily cultured in the laboratory, and because they are sensitive to common disinfection methods, they are used as indicators of potential contamination by other microorganisms (bacteria, viruses, and protozoa). The total coliform bacteria test is a primary indicator of the 'potability' of water.

Figure 2. Total Coliform, Fecal Coliform and E. coli. (Akter, R. 2019)

• What is the criteria for total coliforms?

The standard for total coliform bacteria in drinking water is less than 1 or zero colony-forming-units per 100 mL of water sample. This means that there should be no such bacteria in the drinking water.

• What are the health risks for total coliform bacteria?

The presence of total coliform bacteria indicates that other disease-causing organisms may be present in the water. These other organisms may be associated with bloody diarrhea, stomach cramps, vomiting, fever, respiratory tract infections, urinary tract infections, and even death.

Presence/Absence Tests - Colorimetric Titration

BOC Sciences has applied our presence/absence coliform test in a laboratory setting to detect coliforms in a water treatment plant or water distribution system. A 100 mL test sample is inoculated into a culture flask to obtain qualitative information on the presence or absence of coliforms by the presence or absence of lactose fermentation. Our method maximizes the detection of coliforms in water samples containing many organisms that may allow coliform overgrowth and cause detection problems.

• We collect 100 mL of sample in a sterile container, and aseptic technique is used to prevent contamination
• Then, we add the sample to a sterilized sampling vial
• Next, we add the contents of the ampoule to the bottle. The sample is incubated at 35 ± 0.5 °C (95 ± 0.9 °F) for 24 hours
• After 24 hours, we look for a color change. If there is no color change, the sample is incubated for another 24 hours. If there is no color change after 48 hours, the test result is negative. If there is a color change, the test result is presumptive positive

Advantages of Presence/Absence Tests

• Cost effective
• Simple to perform
• Require less laboratory equipment