MacConkey agar - wikipedia MacConkey agar A MacConkey agar plate with an active bacterial culture. Lactose MacConkey agar with LF and non-LF colonies MacConkey agar is an indicator, a selective and differential culture medium for bacteria designed to selectively isolate Gram - negative and enteric ( normally found in the intestinal tract ) bacilli and differentiate them based on lactose fermentation. The crystal violet and bile salts inhibit the growth of gram - positive organisms which allows for the selection and isolation of gram - negative bacteria. Enteric bacteria that have the ability to ferment lactose can be detected using the carbohydrate lactose, and the pH indicator neutral red. Contents 1 Contents 2 History 3 Uses 3.1 Lac positive 3.2 Lac negative 3.3 Slow 3.4 Mucoid colonies 4 Variant 5 See also 6 References Contents It contains bile salts ( to inhibit most Gram - positive bacteria ), crystal violet dye ( which also inhibits certain Gram - positive bacteria ), neutral red dye ( which turns pink if the microbes are fermenting lactose ). Composition : Peptone -- 17 g Proteose peptone -- 3 g Lactose -- 10 g Bile salts -- 1.5 g Sodium chloride -- 5 g Neutral red -- 0.03 g Crystal violet -- 0.001 g Agar -- 13.5 g Water -- add to make 1 litre ; adjust pH to 7.1 + / − 0.2 There are many variations of MacConkey agar depending on the need. If the spreading or swarming of Proteus species is not required, sodium chloride is omitted. Crystal violet at a concentration of 0.0001 % ( 0.001 g per litre ) is included when needing to check if Gram - positive bacteria are inhibited. MacConkey with sorbitol is used to isolate E. coli O157, an enteric pathogen. History The medium was developed by Alfred Theodore MacConkey while working as a bacteriologist for the Royal Commission on Sewage Disposal. Uses Using neutral red pH indicator, the agar distinguishes those Gram - negative bacteria that can ferment the sugar lactose ( Lac+ ) from those that can not ( Lac - ) fermentation. This medium is also known as an `` indicator medium '' and a `` low selective medium ''. Presence of bile salts inhibits swarming by Proteus species. Lac positive By utilizing the lactose available in the medium, Lac+ bacteria such as Escherichia coli, Enterobacter and Klebsiella will produce acid, which lowers the pH of the agar below 6.8 and results in the appearance of pink colonies. The bile salts precipitate in the immediate neighbourhood of the colony, causing the medium surrounding the colony to become hazy. Lac negative Non-lactose fermenting bacteria such as Salmonella, Proteus species, Yersinia, Pseudomonas aeruginosa and Shigella. Slow Some organisms ferment lactose slowly or weakly, and are sometimes put in their own category. These include Serratia and Citrobacter. Mucoid colonies Some organisms, especially Klebsiella and Enterobacter, produce mucoid colonies which appear very moist and sticky. This phenomenon happens because the organism is producing a capsule, which is predominantly made from the lactose sugar in the agar. Variant A variant, sorbitol - MacConkey agar, ( with the addition of additional selective agents ) can assist in the isolation and differentiation of enterohemorrhagic E. coli serotype E. coli O157 : H7, by the presence of colorless circular colonies that are non-sorbitol fermenting. See also R2a agar MRS agar ( culture medium designed to grow Gram - positive bacteria and differentiate them for lactose fermentation ). References Jump up ^ `` tmc.edu ''. Archived from the original on 2008 - 11 - 04. Jump up ^ Anderson, Cindy ( 2013 ). Great Adventures in the Microbiology Laboratory ( 7th ed. ). Pearson. pp. 175 -- 176. ISBN 978 - 1 - 269 - 39068 - 2. Jump up ^ `` Archived copy ''. Archived from the original on 2010 - 12 - 03. Retrieved 2011 - 03 - 20. Jump up ^ MacConkey AT ( 1905 ). `` Lactose - Fermenting Bacteria in Faeces ''. J Hyg ( Lond ). 5 ( 3 ) : 333 -- 79. doi : 10.1017 / s002217240000259x. PMC 2236133. PMID 20474229. Jump up ^ MacConkey AT ( 1908 ). `` Bile Salt Media and their advantages in some Bacteriological Examinations ''. J Hyg ( Lond ). 8 ( 3 ) : 322 -- 34. doi : 10.1017 / s0022172400003375. PMC 2167122. PMID 20474363. Jump up ^ Luis M. De LA Maza ; Pezzlo, Marie T. ; Janet T. Shigei ; Peterson, Ellena M. ( 2004 ). Color Atlas of Medical Bacteriology. Washington, D.C : ASM Press. p. 103. ISBN 1 - 55581 - 206 - 6. CS1 maint : Multiple names : authors list ( link ) Jump up ^ `` Medmicro Chapter 26 ''. Archived from the original on 2008 - 07 - 06. Retrieved 2008 - 12 - 11. Growth media / agar plates Selective media Gram positive Actinobacteria Mycobacterium tuberculosis Löwenstein -- Jensen medium Middlebrook 7H9 Broth Middlebrook 7H10 Agar Middlebrook 7H11 Agar Mycoplasma pneumoniae Eaton 's agar Firmicutes Corynebacterium diphtheriae Hoyle 's agar Enterococcus Bile esculin agar Lactobacillus MRS agar Lactococcus M17 agar Staphylococcus Mannitol salt agar Gram negative Alphaproteobacteria Brucella Brucella agar Farrell 's medium Betaproteobacteria Neisseria Thayer - Martin agar Gammaproteobacteria Bordetella Bordet - Gengou agar Enterobacteriaceae VRBD agar Haemophilus influenzae / Legionella pneumophila Buffered charcoal yeast extract agar Pseudomonas aeruginosa Cetrimide agar Salmonella XLT agar DCA agar Salmonella / Shigella XLD agar Differential media Lactose fermenting gram negative MacConkey agar / Sorbitol - MacConkey agar Eosin methylene blue Hektoen enteric agar sulfur Bismuth sulfite agar Fungal media Czapek medium Dermatophyte test medium Potato dextrose agar Sabouraud agar Nonselective media Chocolate agar Nutrient agar Plate count agar Other / ungrouped media Cystine -- lactose -- electrolyte - deficient agar Cystine tryptic agar Endo agar Lysine iron agar Müller - Hinton agar / PNP agar R2a agar Simmons ' citrate agar Trypticase soy agar Tryptic soy broth TSI slant Retrieved from `` https://en.wikipedia.org/w/index.php?title=MacConkey_agar&oldid=839915408 '' Categories : Microbiological media Cell culture media Hidden categories : CS1 maint : Multiple names : authors list Talk Contents About Wikipedia Català Čeština Deutsch Español 한국어 Italiano עברית മലയാളം 日本 語 Polski Português ไทย 中文 5 more Edit links This page was last edited on 6 May 2018, at 15 : 05 ( UTC ). 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Question: what types of organisms will grow on macconkey agar
Answer: Gram-negative and enteric (normally found in the intestinal tract) bacilli