Final answer:
Coliforms are gram-negative rod bacteria that ferment lactose and serve as indicator organisms for fecal contamination in water. They are identified and quantified in water testing by their ability to ferment lactose, causing a pH-dependent color change in the test medium.
Step-by-step explanation:
Coliforms are gram-negative rod bacteria that can ferment lactose. They serve as indicator organisms for potential fecal contamination, which is why their presence in water supplies is taken with such seriousness. Some can be pathogenic, like certain strains of Escherichia coli, which are also coliforms and can produce toxins, emphasizing the need for accurate identification and quantification in water testing procedures. In a testing methodology, water samples undergo a series of dilutions and are inoculated in lactose broth tubes; growth is indicated by a color change from red to yellow, influenced by a pH indicator reacting to the fermentation process. The number of coliforms present is then estimated using statistical models based on the observed growth across the dilutions.