How can water be tested for bacteria contamination

Testing water for bacterial contamination is crucial for health safety and environmental monitoring.

Six techniques are being discussed here.

• Membrane Filtration (MF) Technique: In this method, a specified volume of water passes through a fine membrane filter that traps bacteria on its surface. The filter is then placed on a nutrient-rich medium, incubated, and checked for bacterial colony growth. Each colony represents one bacterial cell or cluster in the original sample. This method is used to identify fecal indicators like Escherichia coli and Coliforms in drinking water.

• Multiple-Tube Fermentation (MTF): Water is diluted and added to a series of tubes with a growth medium that supports bacterial growth, leading to gas formation or color change if bacteria are present. Based on the number of positive tubes, the bacterial concentration is estimated statistically (MPN).
• Presence/Absence (P/A) Testing: In a P/A test, a sample is added to a single container with a color-changing or fluorescing growth medium that indicates bacterial presence if the color shifts after incubation.
• Enzyme-Substrate Reaction Tests (e.g., Colilert): Water is mixed with reagents that react with specific enzymes produced by E. coli and Coliforms, creating a visible color change or fluorescence when these bacteria are present.

• PCR (Polymerase Chain Reaction) Testing: PCR amplifies bacterial DNA from a water sample, allowing precise detection of specific pathogens. It involves DNA extraction, amplification using bacterial gene markers, and identification through analysis.
• Flow Cytometry : It uses lasers to count bacterial cells as they pass through a flow cell, with fluorescent dyes differentiating live and dead cells. It provides immediate data on bacterial concentration and activity.

Each method has unique benefits for detecting bacteria in water, with applications ranging from basic field testing to advanced lab analysis. The choice depends on the level of detail needed, resources, and the type of water source being analyzed.