Hi Tiffany, I hope this helps:
Similar Question
a water 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?
Answer:
Coli forms are natural flora of gut of many vertebrates. Their presence indicates a recent fecal contamination of water. Since most of the water borne bacterial pathogens enter the water through excreta or feces, their presence is an indication of possible presence of pathogens. However, even though water samples are negative for Enterobacter or E. coli, the water could still be a public threat because the source of microbes may still enter water through other sources.
* Coli forms are only indicator organisms which gives us the probability of water to have potential pathogens.
In municipal water supplies, the source organism may enter through leaks of water supply pipes, or they might develop from the biofilms formed within the pipes.
The coli forms might be eliminated during the water treatment procedures, but resistant organisms may still survive
Most of the treatment procedures aim only at bacteria or certain viruses, but the remaining virus, protozoan parasites, helminth parasites, and bacterial spores may not be eliminated.
B.Culture media may contain components like antibiotics or serum which detoriate upon heat sterilization. Hence, they are sterilized through filtration. Moreoever, culture media are generally of small volumes and can be sterilized trough filtration.
Filtration in water treatment generally involves removal of large particles. Municiapl water treatments cannot filter water through the same process as that of culture media, since large volumes of water samples may make the filtration membranes inefficient by blocking/clogging the pores. The process is expensive. Therefore, sanitation process uses cheaper procedures.
c. In membrane filtration technique, each colony is assumed to have developed from a viable bacteria, and each viable bacteria gives rise to a colony. However, in true case, two or more bacteria may form a colony.
d. E.coli is positive for Indole and methyl red, but negative for Voges-proskaur and Citrate utilization tests
Enterobacter aerogenes is negative for Indole and methyl red, but positive for Voges-proskaur and Citrate utilization tests
e. Yes. Though EMB is inhibitory to Gram positive organisms, some Streptococci and Staphylococci, and yeasts can grow on this agar. Therefore, it is necessary to perform Gram staining to avoid false positive results.
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