by Medical Lab Notes
Introduction
Table of Contents
SIM stands for sulfide, Indole, and Motility and SIM medium is applied for the differentiation of gram-negative enteric bacilli. SIM test assists to isolate the bacteria on the basis of sulfide production,indole formation, and motility and thus SIM test is a combination of three tests in a single test tube.
Principle of SIM Test
The medium has the constituents ferrous ammonium sulfate and sodium thiosulfate, which together serve as indicators for the production of hydrogen sulfide (H2S). H2S production detects when ferrous sulfide, a black precipitate, is produced as a result of ferrous ammonium sulfate reacting with hydrogen sulfide gas. Casein peptone of this medium is rich in tryptophan. Bacteria having the enzyme tryptophanase degrade tryptophan to indole. Indole detection is achieved after the addition of Kovac’s reagent following incubation of the inoculated medium. Indole combines with p-dimethylaminobenzaldehyde and produces a red band at the top of the medium. A negative indole test produces no color change after the addition of Kovac’s reagent (yellow color of Kovac’s reagent). A lower concentration of agar (0.2-0.4%) added to the medium provides a semi-solid structure allowing for the detection of bacterial motility.Motile bacteriadiffuse from the stab line and produce turbidity or cloudiness throughout the medium. The growth of non-motile bacteria is restricted along the stab line and leaves the surrounding medium clear. Another constituent, animal tissue of this medium which provides amino acids and nutrients necessary for bacterial growth.
Composition of the SIM Medium
- Ingredients for 100 ml of distilled water-
- Pancreatic Digest of Casein: 2.0gm
- Peptic Digest of Animal Tissue (PDAT): 0.61gm
- Ferrous Ammonium Sulfate: 0.02gm
- Sodium Thiosulfate: 0.02gm
- Agar: 0.35gm
- Final pH 7.3 +/- 0.2 at 25°C.
Requirements for SIM Test
- Test organisms
- SIM medium
- Inoculating wire
- Bunsen burner
- Incubator
Quality control strains
- Escherichiacoli ATCC25922
- Salmonella entericaATCC14028
Procedure of SIM Test
- Pick up pure colonies from an 18-24-hour old culture on a solid medium.
- Inoculate the SIM medium by stabbing the center of the medium to a depth of half an inch.
- Incubate the inoculated medium aerobically at 37°C for 18-24 hours.
- Observe for H2S production and motility of test organism.
- Only use Kovac’s reagent (three drops ) after reading the result of H2S and motility reaction to the surface of the medium.
- Observe for the development of a pink to red color.
- Follow the same above steps for control strains too for validation the test procedure.
Result interpretation of SIM Test
- H2S test Positive:Blackening of the test medium
- H2S test Negative:Absence of blackening in the medium
- Motility test Positive:A diffuse zone of growth flaring from the line of inoculation
- Motility test Negative:Restricted growth along the stab line
- Indole positive test:A pink to red color ring is formed at the top of the medium after the addition of Kovac’s reagent.
- Indole negative test:A yellow color denotes a negative indole test after the addition of Kovac’s reagent
- Escherichiacoli ATCC25922:Growth;Motility: positive, H2S: negative, and Indole: positive (It turns pink after addition of Kovac’s reagent)
- Salmonella entericaATCC14028:Growth;Motility: positive, H2S: positive, and Indole: negative
Limitations of SIM Test
- Caps or cotton plug should be loose during incubation otherwise erroneous results may occur
- The inoculum should take from a solid medium since a liquid or broth suspension will delay the initiation of growth and may cause erroneous results.
- When inoculating semi-solid media, it is important that the inoculating needle be removed along the exact same line used to inoculate the medium. A fanning motion may result in growth along the stab line that may result in a false-positive interpretation.
- Take motility and hydrogen sulfide (H2S) reaction results prior to the addition of Kovac’s reagent.
- Weakly motile organisms or organisms that possess damaged flagella (due to heating, shaking, or other trauma) often result in false-negative motility tests, and therefore, motility results should be confirmed by performing a hanging drop motility test.
- Some bacteria likeYersinia enterocoliticademonstrates motility best at 25°C.
- Obligate aerobes like Pseudomonas aeruginosa, will produce a spreading film on the surface of the medium and will not extend from the line of inoculation where oxygen is depleted.
Further Readings
- Cowan and Steel’s Manual for identification of Medical Bacteria. Editors: G.I. Barron & R.K. Felthani, 3rd ed 1993, Publisher Cambridge University Press.
- Textbook of Diagnostic Microbiology. Editors: Connie R. Mahon, Donald G. Lehman & George Manuselis, 3rd edition2007, Publisher El
- Bailey & Scott’s Diagnostic Microbiology. Editors: Bettey A. Forbes, Daniel F. Sahm & Alice S. Weissfeld, 12th ed 2007, Publisher Elsevier.
- Colour Atlas and Textbook of Diagnostic Microbiology. Editors: Koneman E.W., Allen D.D., Dowell V.R. Jr, and Sommers H.M.
- Clinical Microbiology Procedure Handbook Chief in editor H.D. Isenberg, Albert Einstein College of Medicine, New York, Publisher ASM (American Society for Microbiology), Washington DC.
- Jawetz, Melnick and Adelberg’s Medical Microbiology. Editors: Geo. F. Brook, Janet S. Butel & Stephen A. Morse, 21st ed 1998, Publisher Appleton & Lance, Co Stamford Connecticut.
- Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmous, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Franscisco 1996.
Read Also...
- Indole test: Introduction, Principle, Test Requirements,…
- Triple Sugar Iron (TSI) Agar Test: Introduction,…
- Biochemical Test of Gram-Negative Bacteria: Introduction,…
- Salmonella Typhi: Introduction, Identification Features,…
- Robertson’s Cooked Meat (RCM) Medium: Introduction,…
- Citrate Utilization Test: Introduction Principle, Procedure,…
- Citrobacter freundii: Introduction, Identification Features,…
- Phenylalanine Deaminase (PDA) Test: Introduction, Principle,…
20 thoughts on “SIM Test: Introduction, Principle, Test Requirements, Procedure, Result Interpretation, and Limitations”
Just want to say your article is as astonishing. The clearness in your post is simply cool and i can assume you’re an expert on this subject. Well with your permission allow me to grab your feed to keep updated with forthcoming post. Thanks a million and please keep up the gratifying work.
(Video) Lab Results, Values, and Interpretation (CBC, BMP, CMP, LFT)Reply
I believe that is one of the such a lot vital info for me. And i’m glad studying your article. However wanna observation on some normal things, The site taste is great, the articles is really great : D. Good job, cheers
Reply
See AlsoLatest Update Bihar Board 10th Result 2020 Download - बिहार बोर्ड मेट्रिक 10वीं का परिणाम आज 12.30 बजे तक | देखे रिजल्ट लिंक www.biharboardonline.bihar.gov.in - Sarkari Exam HelpHow to Measure Brand Awareness: Metrics, Tools, and KPIsInternships in ChinaHepatozelluläres Karzinom - Symptome, Diagnostik, Therapie | Gelbe ListeI loved as much as you’ll receive carried out right here. The sketch is tasteful, your authored subject matter stylish. nonetheless, you command get bought an impatience over that you wish be delivering the following. unwell unquestionably come further formerly again as exactly the same nearly a lot often inside case you shield this hike.
Reply
This really answered my problem, thank you!
Reply
You made some clear points there. I did a search on the topic and found most individuals will approve with your blog.
Reply
Just wanna tell that this is invaluable, Thanks for taking your time to write this.
Reply
(Video) Benedict’s Test for Reducing sugars - Principle, Composition || #Usmle biochemistryThank you for sharing excellent informations. Your site is so cool. I’m impressed by the details that you have on this blog. It reveals how nicely you perceive this subject. Bookmarked this web page, will come back for more articles. You, my friend, ROCK! I found simply the info I already searched all over the place and simply couldn’t come across. What a perfect web-site.
Reply
Perfect piece of work you have done, this site is really cool with wonderful info .
Reply
Deference to article author, some excellent information .
Reply
I will right away grab your rss feed as I can not to find your e-mail subscription hyperlink or newsletter service. Do you have any? Kindly allow me recognize so that I may subscribe. Thanks.
Reply
(Video) Oxidase Test Procedure and Result InterpretationWhat’s Happening i am new to this, I stumbled upon this I’ve found It positively useful and it has aided me out loads. I hope to contribute & help other users like its aided me. Good job.
Reply
Hello, you used to write great, but the last several posts have been kinda boring… I miss your tremendous writings. Past few posts are just a little bit out of track! come on!
Reply
I am lucky that I observed this weblog, precisely the right information that I was looking for! .
Reply
Very interesting topic, thank you for putting up.
Reply
I’m curious to find out what blog platform you’re using? I’m experiencing some small security issues with my latest website and I’d like to find something more safeguarded. Do you have any recommendations?
(Video) 2-Minute Neuroscience: Electroencephalography (EEG)Reply
I like what you guys are up also. Such clever work and reporting! Keep up the excellent works guys I have incorporated you guys to my blogroll. I think it’ll improve the value of my website :).
Reply
Good website! I really love how it is simple on my eyes and the data are well written. I’m wondering how I might be notified whenever a new post has been made. I’ve subscribed to your feed which must do the trick! Have a great day!
Reply
I like this web site so much, bookmarked.
Reply
Absolutely written content material, appreciate it for selective information.
Reply
My partner and I stumbled over here different web address and thought I may as well check things out. I like what I see so now i’m following you. Look forward to looking into your web page for a second time.
Reply
See AlsoDog Stung by Wasps? 8 symptoms to watchInternships Abroad | CRCC Asia | The Leading Global ProviderTop and Best Microbiology Books (Updated 2022)10 Instruments Used in Microbiology Laboratory - Principle and Uses | Biology Ideas(Video) RT-PCR made EASY - Reverese Transcriptase PCR for detection and test of Viral DNA
Leave a Comment
FAQs
What is the principle of indole test? ›
The indole test screens for the ability of an organism to degrade the amino acid tryptophan and produce indole. It is used as part of the IMViC procedures, a battery of tests designed to distinguish among members of the family Enterobacteriaceae.
What is the principle of catalase test? ›The catalase test tests for the presence of catalase, an enzyme that breaks down the harmful substance hydrogen peroxide into water and oxygen. If an organism can produce catalase, it will produce bubbles of oxygen when hydrogen peroxide is added to it.
What is the purpose of Kovac's reagent? ›Our Kovacs Reagent is used to detect the presence of indole, which is one of the end products from bacterial oxidation of the amino acid, tryptophan. Tryptophan is an amino acid that can be oxidized by some bacteria to form three major end products: indole, pyruvic acid, and ammonia.
What does the MR test determine? ›The methyl red (MR) test detects the production of sufficient acid during the fermentation of glucose and the maintenance of conditions such that the pH of an old culture is sustained below a value of about 4.5, as shown by a change in the color of the methyl red indicator which is added at the end of the period of ...
What are the limitations of indole test? ›Limitations of Indole Test
Additional biochemical testing using pure cultures is recommended for complete identification. The tube test is a more sensitive method of detecting indole than the spot test. When performing a spot test, Kovacs Indole Reagent may be used as a substitute for the spot test reagent.
The citrate test screens a bacterial isolate for the ability to utilize citrate as its carbon and energy source (3, 7). A positive diagnostic test rests on the generation of alkaline by-products of citrate metabolism. The subsequent increase in the pH of the medium is demonstrated by the color change of a pH indicator.
What are the 4 key steps for identifying unknown bacteria? ›- staining the unknown for initial characterization by microscopy.
- using a dichotomous key strategy to systematically rule out other organisms.
- testing the organism for key biochemical traits.
The oxidase test is a biochemical reaction that assays for the presence of cytochrome oxidase, an enzyme sometimes called indophenol oxidase (2, 10, 12). In the presence of an organism that contains the cytochrome oxidase enzyme, the reduced colorless reagent becomes an oxidized colored product (2, 4, 9).
Why is a catalase test important? ›The catalase test facilitates the detection of this enzyme in bacteria. It is essential for differentiating catalase-positive Micrococcaceae from catalase-negative Streptococcaceae. While it is primarily useful in differentiating between genera, it is also valuable in speciation of certain gram positives.
What are the components of Kovacs reagent? ›Kovac′s reagent is prepared by mixing p-dimethylaminobenzaldehyde, isoamyl alcohol and concentrated hydrochloric acid. For identification of an organism, the formation of Indole from a tryptophan substrate is a useful diagnostic tool. Indole production is a crucial test in identification of Escherichia coli.
What is the main ingredient of Kovac's reagent? ›
The active ingredient in Kovacs reagent, p-Dimethylaminobenzaldehyde, reacts with indole to form a highly visible pinkish-red end product.
Who discovered Kovacs reagent? ›Invented by the Hungarian-Swiss chemist Ervin Kovats (Kovacs) (1927–2010).
What does negative MR test mean? ›MR Positive: The culture medium turns red (because the pH of the medium is at or below 4.4 from the fermentation of glucose). MR Negative: Culture medium remains yellow (less acid is produced from the fermentation of glucose).
How do you perform a MR test? ›- Inoculate MRVP broth with a pure culture of the organism.
- Incubate at 35°-37°C for a minimum of 48 hours in ambient air.
- Add 5 or 6 drops of methyl red reagent per 5 mL of broth.
- Observe for the color change in the broth medium.
This test is used to determine which fermentation pathway is used to utilize glucose. In the mixed acid fermentation pathway, glucose is fermented and produces several organic acids (lactic, acetic, succinic, and formic acids).
What color is a positive indole test? ›Indole, if present, combines with the aldehyde in the reagent to produce a pink to red-violet quinoidal compound (if benzaldehyde reagent is used) or a blue to green color (if cinnamaldehyde reagent is used). The absence of enzyme results in no color production (i.e. indole negative).
What is indole used for? ›Indole-3-carbinol is used for prevention of breast cancer, colon cancer, and other types of cancer. The National Institutes of Health (NIH) has reviewed indole-3-carbinol as a possible cancer preventive agent and is now sponsoring clinical research for breast cancer prevention.
What is the significance of indole? ›Indole has recently been implicated as an important small molecule signal utilized by many bacteria to coordinate various forms of behavior. Indole plays a role in numerous bacterial processes, including: biofilm formation and maintenance, virulence factor production, antibiotic resistance and persister cell formation.
What does a positive result for citrate test mean? ›A positive reaction shows that the organism can use citrate but not necessarily as the sole carbon source.
Which media is used for citrate test? ›Simmon's Citrate agar is used as the medium to test the ability of an organism to utilize citrate as a sole source of energy.
What does a positive citrate test look like? ›
The alkaline pH turns the pH indicator (bromthymol blue) from green to blue. This is a positive result (the tube on the right is citrate positive). Klebsiella pneumoniae and Proteus mirabilis are examples of citrate positive organisms.
What is the principle of biochemical test? ›The ability of microorganisms to utilize certain biomolecules, resulting in useful organic compounds for themselves forms the basis of various biochemical tests. Biochemical tests are of different types, where the identification or distinction between different microorganisms is made on various bases.
What is the principle of oxidase test? ›The oxidase test is a biochemical reaction that assays for the presence of cytochrome oxidase, an enzyme sometimes called indophenol oxidase (2, 10, 12). In the presence of an organism that contains the cytochrome oxidase enzyme, the reduced colorless reagent becomes an oxidized colored product (2, 4, 9).
Which reagent is used in indole test? ›Detection of indole is based on the chemical reaction between indole and Kovac's reagent (isoamyl alcohol, para-dimethylaminobenzaldehyde, concentrated hydrochloric acid) under acidic conditions: Para-Dimethylaminobenzaldehyde reacts with the indole present in the medium to form a rosindole red dye.
Which bacteria is indole positive? ›Indole-Positive Bacteria
Bacteria that test positive for cleaving indole from tryptophan include: Aeromonas hydrophilia, Aeromonas punctata, Bacillus alvei, most Citrobacter spp., Edwardsiella spp., Escherichia coli, Flavobacterium spp., Haemophilus influenzae, most Proteus spp.
- Catalase Test.
- Mannitol Salt Agar (MSA)
- Blood Agar Plates (BAP)
- Streak-stab technique.
- Taxos P (optochin sensitivity testing)
- Taxos A (bacitracin sensitivity testing)
- CAMP Test.
- Bile Esculin Agar.
The Clinical Biochemistry Laboratory's sophisticated, automated operations support both routine and urgent testing. The lab's efficient systems enable routine testing for more than 30 different tests using only a single tube of blood.
Why is biochemical test important? ›Biochemical reactions can reveal the vital information necessary for accurately identifying the genera of various bacteria within a sample. By their nature, bacteria produce large volumes of enzymes, and it is these enzymes that allow for their identification via biochemical methods.
What are the 4 key steps for identifying unknown bacteria? ›- staining the unknown for initial characterization by microscopy.
- using a dichotomous key strategy to systematically rule out other organisms.
- testing the organism for key biochemical traits.
Oxidase positive: color changes to dark purple within 5 to 10 seconds. Delayed oxidase-positive: color changes to purple within 60 to 90 seconds. Oxidase negative: color does not change or it takes longer than 2 minutes.
Which bacteria is oxidase positive? ›
Oxidase Positive Bacteria
anthracis / Cordiobacterium hominis / Bac. subtillis / Pseudomonas spp. / Brucella spp. / Flavobacterium spp. / Chromobacterium spp. / Alcaligenes spp. / Eikenella corrodens / Moraxella spp. / Plesiomonas spp. / Campylobacter spp. / Branhamella catarrhalis / Micrococcus spp.
Indole production is often used to differentiate E. coli from other indole-negative enteric bacteria because 96% of E coli are indole positive, whereas many enterobacterial species are negative in the indole reaction.
What bacteria are indole negative? ›Bacteria which give negative results for the indole test include: Actinobacillus spp., Aeromonas salmonicida, Alcaligenes sp., most Bacillus sp., Bordetella sp., Enterobacter sp., most Haemophilus sp., most Klebsiella sp., Neisseria sp., Mannheimia haemolytica, Pasteurella ureae, Proteus mirabilis, P.
Is E coli citrate positive or negative? ›Escherichia coli and Shigella dysenteriae are citrate negative.
Is E coli Gram-negative? ›Examples of Gram-negative bacteria include Escherichia coli (E coli), Salmonella, Hemophilus influenzae, as well as many bacteria that cause urinary tract infections, pneumonia, or peritonitis.
Is E coli oxidase positive? ›E. coli bacteria are among the few species of lactose (LAC)-positive, oxidase-negative, gram-negative rods that are indole positive.
Why do bacteria need indole? ›Indole has recently been implicated as an important small molecule signal utilized by many bacteria to coordinate various forms of behavior. Indole plays a role in numerous bacterial processes, including: biofilm formation and maintenance, virulence factor production, antibiotic resistance and persister cell formation.