The picture shows litmus test results using apple juice, milk and lake water as real-life samples, along with clean water as a negative control (NC). Photos are taken when litmus test just begins (0 min) and proceeds for 15, 30, and 60 minutes. NC sample does not change colour over time (first column). For apple juice, milk, and lake water samples: “-“ means that each given sample that does not contain E. coli (thus each solution does not change colour at all with time); “+” means a relevant sample with E. coli (that’s why the solution changes colour even within 15 minutes, and exhibits increasingly stronger colour change with time)

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