Identifying unknown bacteria

About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.

Moderators: Leonid, amiradm, BioTeam

Post Reply
Posts: 3
Joined: Fri Nov 23, 2007 2:07 am

Identifying unknown bacteria

Post by hiimkimmie » Fri Nov 23, 2007 2:14 am

hey, i need help in identifying an unknown bacteria for my microbiology class. my professor said we arn't being held to know exactly what it is, but what catagory or direction it is. this is what all i have so far:

it is a gram - cell.
it presents catalase because it bubbled.
amalase is present because starch was digested.
it does not have casinase because it did not digest pepsin.
it is aerobe, an obligate aerobe because it must have oxygen
it will not grow in TSI, triple sugar iron and
it will not grow in SCA, simmons citrate agar

it is bacilli because it is rod shaped, and the color of it was an offwhite color. please help me!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Posts: 3
Joined: Fri Nov 23, 2007 2:07 am

Post by hiimkimmie » Sat Nov 24, 2007 1:54 am

ok, so i emailed my professor and here was his reply:

Keep in mind that for the unknown report, the goal is not to necessarily identify
the unknown, but rather to demonstrate your ability to interpret and reason through
your results. So, it is quite possible, especially based on the results you
outlined below, that you will not identify your bacterium. That is okay...what you
will do then is, in your conclusion, talk about how your results are not sufficient
to identify your unknown.

For example, you could say, 'While I have shown that unknown #3 is a gram (-)
bacillus, facultative aerobe, thus far not enough data has been gathered to
definitively identify this bacterium. Based on this observations, I am confident
that this bacterium belongs to the coliform family. Within that family, there are a
number of possibilities for this unknown including X, Y and Z. To differentiate
between these possibilities, one would perform the following tests.' And then go
from there, indicating possible tests and expected results.

I can tell you that you do have a coliform as you correctly surmised below. The
bacterium is potentially pathogenic, but we have done no direct test to show that in
the lab.

In terms of growth on the specialty medias (lab #12), how did your bacterium grow on
the Levine-EMB? I would have expected a purplish tinted, sticky looking pattern of
colonies. Also, your unknown should have grown on both Simmons Citrate Agar (SCA)
and the Triple Sugar Iron (TSI). In fact, every unknown in the class, except #14,
should grow on TSI. The lack of growth you noted on both of those media may be what
is causing your frustration. SO, what you could say is that 'Identification of this
unknown would have been helped had the bacterium grown on TSI and SCA.
Unfortunately, that did not occur. One possible reason is..." and then try to come
up with a reason for lack of growth. Keep in mind that we are dealing with living
organisms and cannot expect everything to work everytime. And that is okay and will
not penalize your long as you mention that those tests may have been
helpful. In fact, I would even go on to say in your unknown report that, if time
permitted, it would be helpful to repeat the TSI and SCA tests and to do the
following determination (and then mention another possibly helpful test or result
that you stumbled across in your readings).

In terms of the production of hydrogen sulfide...we did that test in lab, but it was
not the hydrogen peroxide bubbling (catalase) test. Rather, if a bacterium produces
hydrogen sulfide, then in the TSI tubes you would get black deposits in the bottom
of the TSI tube

Think back to your TSI it possible that there was growth, but no dramatic
change in color? I think it was very likely that, because I remember checking
everyone's tubes the day before and seeing growth in the TSI tubes. I will admit to
not checking the SCA tubes for everyone, though, so I can't help you there.


is it possible i have e.coli? please help me! i dont want to be wrong!

Posts: 4
Joined: Sun Apr 29, 2007 10:26 am

Post by microworld » Sat Nov 24, 2007 9:21 am

Mmm,if you want to identify it exactly,you should do a series physical and biochemical test to verify.
Also, you can use API system et al.There is another way that is detected 16srRNA to get the final answer.
good luck

Posts: 3
Joined: Fri Nov 23, 2007 2:07 am

Post by hiimkimmie » Sat Nov 24, 2007 1:09 pm

what possible tests could i do, to figure out and determine my unknown? like, i know my bacteria is from the coliform group. but there are different bacterias in the coliform group and these certain tests can determine what each is. what would those tests be? thank you! :)

User avatar
Inland Taipan
Inland Taipan
Posts: 5345
Joined: Thu Jan 20, 2005 8:14 pm
Location: Nashville, TN

Post by mith » Sat Nov 24, 2007 5:06 pm

Living one day at a time;
Enjoying one moment at a time;
Accepting hardships as the pathway to peace;

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest