Concept explainers
What is the logic behind testing for E. coli to detect fecal contamination of water?
To determine:
The logic behind testing for E. coli to detect fecal contamination of water.
Introduction:
E. coli is a common inhabitant of the human intestine; it is also able to survive in the outside environment.
Explanation of Solution
Coliforms such as E. coli are used to detect fecal contamination in water samples due to their widespread presence in the human intestine. They are able to survive in the outside environment, and will therefore provide a reasonable inoculum for culture tests. They are also easier to culture than true pathogens. For this reason, they are used as the initial indicator for fecal contamination; their presence indicates the possible presence of true enteric pathogens such as Salmonella.
E. coli is used to detect fecal contamination in water due to the fact that it is a prominent inhabitant of the human intestine, it is able to survive in the environment and it is easier to culture than true enteric pathogens.
Want to see more full solutions like this?
Chapter 20 Solutions
Foundations in Microbiology
- Why do we test water for coliforms if they are not considered pathogenic?arrow_forwardAseptic technique refers to A) the microbial inoculum placed into a test tube or onto a Petri plate. B) a series of practices to avoid contamination. C) the autoclave and other sterilizing procedures. D) cleanliness in the laboratory.arrow_forwardWhy can EMB agar be used to detect the presence of E. coli in particular? Explain the principle of detection of the organism using EMB agararrow_forward
- A stool specimen of a patient with severe diarrhea was cultured in a series of specialized media for isolation of enteric organisms. The cultures yielded three isolates that were species of Salmonella, Shigella, and Escherichia. Explain why the Hydrogen sulfide production test would be diagnostically significant.arrow_forward1) What are all of the different colony types that can be seen on a mixed-culture streak plate? 2) What kinds of colonies can be seen when mixed cultures of E. coli, M. luteus, and Serratia marcesens? 3) What is the range of colonies that may be seen with each mixed culture?arrow_forwardIf coliforms were present on a plated sample, would you know with certainty that the coliforms are disease-causing? Why or why not?arrow_forward
- Transparent double-sided dishes used for growing microbes are most commonly called A) Petri dishes. B) baker dishes. C) sterilization plates. D) culture medium plates.arrow_forwardyou are given a mixed culture of s. aureus, E. coli and P. aeruginosa. how would you isolate each other from this mixed culture?( Besides using plate technique)arrow_forwardKoch's postulates include all of the following EXCEPT O 1) Isolate the organism in pure culture. The symptoms of the test animal may vary from the symptoms seen in the O 2) patient. O 3) Inoculate a test animal with the isolated organism. 4) The organism must be isolated from the test animal in pure culture. 5) The organism isolated from the test animal must match the organism isolated from the patient.arrow_forward
- a) explain in your own words how to do a nitrate reduction test to identify unknown bacteria b) explain in your own words how to perform a phenol red broth (prb) test to help identify unknown bacteriaarrow_forwardE. coli O157:H7 is an organism of concern in contaminated foods. How can the use of MacConkey agar and Sorbitol-MacConkey agar be used to screen for E. coli bacteria in general and E. coli O157:H7 in particular?arrow_forwardIf the concentration of E. coli in a broth is between 104 and 106 cells per mL, the best way determine the precise number of living cells in the sample, would be toa) use a counting chamber.b) plate out an appropriate dilution of the sample on nutrient agar.c) determine cell number by using a spectrophotometer.d) Any of these three methods would be satisfactory.e) None of these three methods would be satisfactory.arrow_forward