Overview of Biochemical tests used to identify bacteria in Microbiology laboratory

Overview of Biochemical tests for differentiating Gram positive cocci
Overview of Biochemical tests for differentiating Gram positive cocci

In this blog post, i am sharing information about common, conventional biochemical tests and their primary uses in Microbiology laboratory for the identification of particular pathogen of interest. Some of the biochemical tests mentioned here for example catalase test, oxidase test assists us in many ways apart from the primary purpose mentioned in this post;

  1. Beta-glucuronidase test (MUG Test) : To identify Escherichia coli. Escherichia coli produces the enzyme β-D-glucuronidase, which hydrolyzes β-D-glucopyranosid-uronic derivatives to aglycons and D-glucuronic acid.

    Overview of Biochemical tests for differentiating Gram positive cocci
    Overview of Biochemical tests for differentiating Gram positive cocci
  2. Bacitracin Sensitivity Test: Bacitracin sensitivity test differentiates Streptococcus pyogenes (positive) from other beta hemolytic streptococci (resistant).
  3. Bile solubility test : To differentiate Streptococcus pneumoniae from other alpha hemolytic streptococci. Bile or a solution of a bile salt, such as sodium desoxycholate rapidly lyses pneumococcal colonies.

    CAMP Test
    CAMP test :
    A. Streptococcus agalactiae (positive)
    B. Streptococcus pyogenes (Negative)
    Image Source: ASM
  4. CAMP Test: Certain organisms such as Streptococcus agalactiae (Group B streptococci), produce a diffusible extracellular protein (CAMP) factor that acts synergistically with the beta-lysin of Staphylococcus aureus and  causes enhanced lysis of RBCs.
  5. Catalase test: To differentiate Staphylococci (catalase positive) from Streptococci (catalase test negative)
  6. Citrate utilization test: To differentiate members of Enterobacteriaceae family.
  7. Coagulase test: Coagualse test is used to identify Staphylococcus aureus. Coagulase test differentiates Staphylococcus aureus (positive) from coagulase negative staphylococci (CONS), such as S. epidermidis, S. saprophyticus.
  8. DNase test: This test is used to determine the ability of an organism to hydrolyze DNA. It is primarlly used to identify Staphylococcus aureus
  9. Indole test: This test is used to determine the ability of an organism to split tryptophan to form the compound indole. It is used differentiate gram negative rods particularly E. coli in microbiology laboratory.
  10. Litmus milk decolorization test: To help identify Enterococcus and some Clostridia which have ability to metabolize litmus milk.
  11. Lysine Decarboxylase test: To assist in the identification of Salmonella and Shigella
  12. Oxidase test: To help identify Neisseria, Pasteurella, Vibrio, and Pseudomonas. This test is used to determine the presence of bacterial cytochrome oxidase.
  13. Urease test: Urease test is used to determine the ability of an organism to produce urease (an enzyme) which hydrolyzes urea. This test is done to help identify Proteus, Morganella, Yersinia enterocolitica, and Helicobacter pylori
About Acharya Tankeshwar 452 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.


    • Pranab Roy
      Thank you for your question. Why you need to differentiate member of Enterobacteriaceae family from that of Rhizobia? I think you never encounter such problem while identifying clinical isolate. Rhizobia are non-fermentative and forms dry, tenacious colonies.

  1. sir i am persuing msc. biochemistry and its my 4th semester . . . can u please suggest me topics for dissertation?

  2. this site is amazing. thank you so much. this help me a lot in my preparation for ASCP exam. more power and God bless

  3. It’s quite clear to understand the basic idea of biochemical tests and expected results, but I wanted to know the limitations in these tests, specifically for oxidase, catalase. If it possible plz give a link even possible

  4. Thanks for the concise and beautiful write up. Please i’ll like to know the biochemical tests for lipase producing microorganisms. Thank you.

  5. please give me detail about the ATCC CULTURE (MICROBIOLOGICS)
    what does it means and how to find out following( if it is on certificate of analysis)
    purity : 0.1% total pellet cfu
    Recovery : >1000 cfu / pellet bacillus subtilis

    • Pham Khan, we do not perform such testing in our laboratory but I think, this linkhttps://www.chemsee.com/commercial/food-poisons/products/ will address your query.

  6. I would like to Request you to provide me any practical concerning bacteria culture ,biochemical test , and Gram negative bacteria that have a resistance to drugs. and i wanted to have a certificate professional on that.

    I.m working for National public Health laboratory in South Sudan and we have a challenges in bacteria culture .
    please tell me if you have a branch for training people , to our neighbor country south Sudan , i may joint you soon .

    my best Regards
    Pham Khan

    • Dear Pham Khan, We have updated blogs about various biochemical tests: https://microbeonline.com/bacterial-identification-methods/, culture media: https://microbeonline.com/culture-media/ etc already in microbeonline. Please go through the relevant post, and if you did not find any content or if you have any query, please let us know, we will try to address your query.
      We are happy to be connected with you and we wish you all the best. We are hopeful, you will strengthen the microbiology laboratory facility of National Public Health Laboratory of South Sudan with your expertise and leadership skills in the days to come. We are sorry, we do not have any branch to train laboratory technician but we are always open to address your issues. As you have said, you have challenges in bacterial culture, if it is related to some information gap, we are ready to provide relevant information based on our experience.

  7. Thank you sir, for your enlightenment. Sir i want to know for in case of urine test examination, is there specific parasite that you can found and others that can be found in urine in rare cases?

  8. sir,
    really this information is more helpful for us but if u add the bacterial colony characteristic of important and common bacteria it will more better to understand the diagnosis of disease and find out etiology of disease.

    thank you

  9. I was reading your comment on id of Vibrio and was a bit confused on your suggestion to perform oxidase
    on maconkey agar.I know that times have changed since I had learnt from my Professor then to never
    perform oxidase on maconkey,because of false results.Please correct me,I am still learning.

    • Dear Yacoob Mohammed,
      Thank you so much for your valuable comment. My understanding is also the same i.e. oxidase test must be performed from sheep blood agar or another medium without a fermentable sugar as acidification of MacConkey agar/TCBS can give false-negative results. I regret the inaccurate information inadvertently shared and will correct it as soon as possible. Thank you once again for helping me to disseminate accurate information to microbiology enthusiasts.

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