Awater sample could be negative for enterococcus and coliforms and still be a major public health threat. why?
why can filitration be used to sterilize culture media? why can filtration be used in sanitation?
what basic assumption is made in the membrance filter technique if the number of bacteria is determined from the number of colonies?
what difference exsits between e. coli and e. aerogenes regarding their imvic reactions?
is it really necessary to perform a gram stain on the microbes isolated from macconkey or eosin-methylene blue agar used in the presumptive identification of coliforms? why or why not?

1. Enterococcus and coliforms can enter the water through feces. Although a water sample is negative for these bacteria, it could still be infected by pathogens from other sources than feces.

2. Culture media are sterilized by filtration because they could contain antibiotics or serum which deteriorate upon heat. Filtration is used in sanitation to remove large particles.

3. In the membrane filter technique, it is assumed that all viable bacteria will form colonies. This means that formed colonies develop from the viable bacteria so that the number of colonies suggests the number of bacteria.

4. E. coli is negative for Citrate and Voges-Proskauer tests, and is positive for Indole and Methyl red tests.

5. The answer is yes because eosin-methylene blue agar is inhibitory to Gram+ bacteria.