Unknown identification

[tmn920]

So we just started identification of our unknown bacteria today in lab. Our teacher didn't really explain much and I'm kind of lost...I was hoping someone could help!! I found it is Gram Negative and Rod-Shaped. I plan on testing for motility and performing the catalase/oxidase tests next. Am I headed in the right direction? I just dont really know what steps to take as far as the order of tests I perform and keeping my culture fresh.

[Cat]

Since your orgnism is gram-ve rod, catalase test in not needed (primarily staph id); oxidase might not be needed either. You might want to look at this id scheme:
http://webpages.marshall.edu/~simerma1/ ... gIDlab.htm

[tmn920]

thank you so much!

[Cat]

You are welcome!

[tmn920]

i'm almost positive that i have enterobacter...the SIM motility test was positive but the media was a little runny so i have to perform the test again. Do you know how I would distinguish between the different species of this genus?

[Cat]

You can ID them by Biochem test panels or DNA. I don’t know what your lab has available (if anything, especially if your class is general micro)…

[Sepals]

Contrary to what Cat said Oxidise and catalyse tests are always important! Like for example Enterbacteriaceae are always oxidise negative and catalyse positive, while Haemophilus is positive for both.

Rather then expect to be spoon fed here you should have already been taught how to identify, if not, you can easily find the info in medical microbiology textbooks. I recommend Color Atlas of Medical Microbiology (Diagnosis in Colour) by C. Anthony Hart and Microbiology: A Photographic Atlas for the Laboratory by Steven K. Alexander and Dennis Strete.

Cat you mean APIs or sequencing (which is reserved for hard to identify organisms). The whole point of doing individual biochemical tests is for the OP (and I) to show we understand the organism we are dealing with.

[Cat]

I did not say that they are not important. I said they are not necessary for ID.

1. If you take all gram -ve bacilli (and Haemophilus is coccobacilli), you cannot use oxidase and catalase tests to ID them the same way can for staph ID among gram +ve cocci.

2. Your example is not relevant to regular micro lab. To isolate Haemophilus you need special media containing X and V factors, blood agar in presence of S. aureus, or chocolate agar. Growth on regular nutrient agar or broth etc. is sufficient to rule out Haemophilus, thus, making any additional tests irrelevant.

[Sepals]

Coccobacilli = very short bacilli. Actually Haemophilus is pleomorphic (it can be observed as a range of different sizes from coccobacilli to longer, filamentous forms).

My example is relevant to a regular micro lab. My course is designed to train people to work in a regular micro lab and much has been covered on Haemophilus. Before the introduction of the vaccine in 1992 ~ 1500 cases of invasive Haemophilus disease including 900 cases of meningisis occured in the UK every year resulting in 60 deaths. Although infection rates have decreased since cases still occur and so an average clinical microbiologist must considered this organism. The oxidise and catalyse tests would be done before the ones you have listed, and is not involved in isolation, rather in pointing a microbiologist in the right direction.

Other gram negative pathogenic bacilli which are oxidise positive include those under the genera Aeromonas (may be a cause of diarrhoea and more serious infections in immunecompromised people) and Vibrio (can result in cholera and other nasty diseases), also the species Pseudomonas aeruginosa (leads to a wide range of illnesses) and Plesiomonas shigelloides which may cause diarrhoea.

[Cat]

There is something that I definitely don’t understand. Sepals, when you are saying “My course”, do you mean that you are teaching the course that tmn920 is taking?

While you are right in terms of the clinical findings etc… , you are overlooking the fact that we are talking about general micro lab (as I understood from tmn920s original message).

In general micro, to get you introduced to bacteria ID process you will be given a plate/broth with unknown bacteria to ID. You will not get to work with pathogens such as Haemophilus or Aeromonas and you will be unlikely to be given any bacteria that are pleomorphic either (to avoid any confusion). The idea of the course is to learn the basics in the lab environment, not in the clinical field.

Your ideas are leaning too heavily toward clinical micro. It seems to me that you are forgetting the lab basics. While nurse/doctor would need to perform oxidase/catalase tests on the nose swab if Haemophilus infection is suspected, they need to do that to either rule it out or to know that it is a possibility and, therefore, culture needs to be done on media containing X and V factors and further tests ordered for confirmation. In the lab, however, if you are given a regular nutrient agar plate with unknown bacteria on it and asked to ID it, your first conclusion should be that it’s not Haemophilus.