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Name: Robinson
Status: Student
Grade:  Other
Location: MN
Country: United States
Date: January 2009

E.coli is a gram -ve bateria. How can one diferentiate otner bacteria that may have same color from E.coli? In other words if you gram stain a bacteria, how do you know it's E.coli

NEWTON BBS does not recommend growing/culturing bacteria without the supervision of a microbiologist, and a properly equipped microbiology laboratory. Safety is our main concern! Growing dangerous bacteria species unknowingly is a real possibility and serious illness may occur without proper handling techniques. Furthermore, without proper bacterial disposal procedures such as an autoclave can guarantee, there is a danger to anyone who comes in contact after disposal.

You don't! If one is a very experienced microbiologist, sometimes bacteria have certain shapes that are unique. But, most gram negative bacteria look very similar. The only way to know for sure if its E coli is to grow it out on media and do biochemical testing to confirm it.


After determining a bacterium is Gram negative, the bacterium's ability to ferment various sugars will distinguish it from other Gram negatives. Also, nowadays bacteria can be distinguished from each other by the nucleotide sequence in their genes that code for ribosomal RNA.

Ron Baker, Ph.D.

There are lots of ways of classifying bacteria. Traditional microbiology lab techniques rely on gram staining as well as other kinds of stains, appearance under microscope (e.g. size and shape), and how colonies look (size, shape, color, margin). You can also use indirect methods such as changing the conditions in which they live (not all bacteria thrive in the same conditions). More modern techniques can sequence DNA to identify not only the species, but even different strains within the same species.

Hope this helps,

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