Which of the following is the ideal indicator for pathogens in water?

The coliform group bacteria serve as the ideal indicator for pathogens in water due to their presence in the intestines of warm-blooded animals, including humans. Their detection suggests possible contamination with fecal material, which may harbor harmful pathogens, including bacteria, viruses, and protozoa. Coliforms are relatively easy to detect and enumerate through well-established laboratory methods, making them practical for water quality monitoring.

In contrast, while Salmonella species can indicate the presence of pathogens, they are not as ubiquitous or easy to detect in water samples as coliforms. The presence of Salmonella does not necessarily reflect the general condition of water with respect to fecal contamination and potential disease-causing organisms.

Gram-negative cocci and Gram-negative coccobacilli are more general classifications of bacteria and do not specifically point to fecal contamination or pathogen presence in water. They may include a variety of non-pathogenic organisms and therefore do not serve effectively as indicators for potential waterborne pathogens.