staphylococcus aureus colony morphology on macconkey agar

CULTURE REQUIREMENTS OF STAPHYLOCOCCUS AUREUS, Various culture media for Staphylococcus aureus , CULTURAL CHARACTERISTICS OF STAPHYLOCOCCUS AUREUS, Thats all about the Morphology & Cultural Characteristics of Staphylococcus aureus, cultural characteristics of staphylococcus, cultural characteristics of staphylococcus aureus, Various culture media for Staphylococcus aureus. aureus is with some frequency found as normal human flora in the anterior nares (nostrils). The present study aimed to characterize S. aureus strains from the oral cavity microflora, isolation of . Examples include Escherichia coli, Klebsiella spp, Citrobacter, Enterobacter, etc.Pale (NLF) and pink (LF) colonies on MacConkey Agar. The media was first developed by Alfred Theodore MacConkey in 20th century. why do staphylococcus aureus look dark red and smooth on Mac conkey agar. 1st session 2nd session 3rd session 4th session, CNA DNAse Coagulase Run other needed tests Identify species, MSA SM110 ONPG. What do the dark pink colonies on MacConkey (MAC) agar? I am Tankeshwar Acharya. Mannitol salt agar (MSA) is a selective, differential, and indicator medium used to isolate and identify Staphylococcus aureus from the clinical specimen. Check the SM 110 for growth and for pigment. 1995. You can also purchase the ready-made MacConkey medium from commercial suppliers. Hemolysin is one of the important virulence factors for S. aureus and causes the typical -hemolytic phenotype which is called complete hemolytic phenotype as well. S. pneumoniae is a fastidious bacterium, growing best at 35-37C with ~5% CO 2 (or in a candle-jar). Circular form. Only firm and complete clot that stays in place when tube is tilted or inverted is considered positive for S. aureus. Or the hemolysis can be a partial breakdown, resulting in a greenish or green-yellow zone around the colony. In some cases, selective and differential characteristics are combined into a single medium. Please suggest . Add 0.5 ml reconstituted coagulase plasma with EDTA (B-4, above) to the BHI culture and mix thoroughly. I share & use your blogs for teaching my Uunder graduate students. Isolation of bacteria is accomplished by growing ("culturing") them on the surface of solid nutrient media. Can you give the test reaction of S. aureus for each of the major tests run---MSA, SM110, coagulase, catalase, oxidase, and DNAse? Made with by Sagar Aryal. Your email address will not be published. Transfer isolated colony from agar plate with inoculating loop to 0.2 ml phosphate-saline buffer, and emulsify. MacConkey agar is used for the isolation of gram-negative enteric bacteria. Staphylococci species can tolerate this salt concentration, but other pathogenic bacteria maynot. ColorGolden yellowPinkLight golden yellow, surrounded by clear zone (beta hemolysis).YellowGolden yellow (Pigment production enhanced). Has a lot of information that you is difficult to find elsewhere. EmulsifiabilityEasily emulsifiableEasily emulsifiableEasily emulsifiableEasily emulsifiableEasily emulsifiable. MSA plates were incubated at 35C for 48 hours. FIG. Incubate plates 48 h at 35-37C. Note: Gram-positive organisms are inhibited in MacConkey agar with bile salts and crystal violet, however, in a different formulation where bile salt and crystal violet are not incorporated, Gram-positive organisms also appear as lactose fermenters but are smaller in size than gram-negative ones. MSA plates with little Hi Commercial nucleic acid amplification tests are available for the direct detection and identification of. Columbia CNA Agar: Composition, Uses, and Results. Thermostable nuclease production. Phenol red pH indicator - yellow in acid pH (the same indicator that is used in phenol red carbohydrate fermentation broths). CULTURAL CHARACTERISTICS OF STAPHYLOCOCCUS AUREUS In liquid culture media like peptone water and Nutrient broth, uniform turbidity is produced which is further analyzed for the morphology (under the microscope), gram reaction, biochemical tests, and staphylococcus specific tests. Table 1. Spherical colonies in clusters in two planes. Cultivation Media for Bacteria. Colonies on solid media are round, smooth, raised, and glistening. Incubate 5 days at 35-37C. Recently, S. aureus with an incomplete hemolytic phenotype (SIHP) was isolated from clinical samples. It is used in the differentiation of lactose fermenting from lactose non-fermenting gram-negative bacteria. Cultivation Media for Bacteria. Methicillin-resistant strains of Staphylococcus aureus (i.e. The other media being used in this exercise are for differentiating pathogenic Staphylococcus from nonpathogenic, and for identification of the species. MRSA) often have only weak or no beta-hemolysis and special cultivation media with oxacillin, mannitol and NaCl for their isolation are used. All six toxins lyse WBC by pore formation in the cellular membranes that increase cation permeability. Development of bright pink halo extending at least 1 mm from periphery of well indicates a positive reaction. Colony Morphology on MacConkey Agar Besides differentiating on the basis of color, colonies on MacConkey medium can further be presumptively identified based on their colonial appearances (shape, size, margin, time of growth, etc). Staphylococcus is a genus of Gram +, nonspore-forming cocci belonging to the family Micrococcaceae that are often found as normal human microbiota of the skin and nasal cavity. Pathogenic staphylococci, i.e. Just curious. It can also be found in the throat, axillae, and the inguinal and perineal areas. Shelf life: Several weeks, providing there is no change in the appearance of the medium to suggest contamination, deterioration, or alteration of pH. Media and reagents--Same as for Direct Plate Count Method, above. )Purpose: Selective and differential; identification of pathogenic Staphylococci . Each table will be given a Staphylococcal species growing on aNA or TSA plate. Be sure to keep a list of all test results for your isolates. Gram-negative bacteria that grow on MacConkey agar but do not ferment lactose appear colorless on the medium and the agar surrounding the bacteria remains relatively transparent. Shouldnt they show no growth? Thus, the presence of this bacterium or its enterotoxins in processed foods or on food processing equipment is generally an indication of poor sanitation. Pls continue your service to Microbiology, Dr. Manjunath Ramanna Scribd il pi grande sito di social reading e publishing al mondo. This method is suitable for the analysis of foods in which more than 100 S. aureus cells/g may be expected. Staphylococcus saprophyticus (coagulse-negative Staphylococci)may ferment mannitol, producing yellow halo around colonies in MSA thus resembling S. aureus. A. Mannitol Salt Agar. Your email address will not be published. Tests for clumping factor, coagulase, hemolysins, and thermostable deoxyribonuclease are routinely used to identify. Hemolysis of blood cells can be very useful as an identification test. Tatini. Agar is obtained from red algae belonging to the genera Gracilaria, Ahnfeltia, Microbeonline.com is an online guidebook on Microbiology, precisely speaking, Medical Microbiology. If the lactose is fermented the production of the acid drops the pH of the media. Sperber, W.H., and S.R. This test is claimed to be as specific as the coagulase test but less subjective, because it involves a color change from blue to bright pink. The red color is due to production ofacid from lactose, absorption of neutral red and a subsequent color change of the dye when the pH of medium falls below6.8. Patients may be given disinfectant baths or treated with a topical antibiotic to eradicate carriage of MRSA. The occurrence of S. aureus under these circumstances What happens to RBCs in beta and alpha hemolysis. Generally associated with intravenous drug users. Columbia CNA Agar: Composition, Uses, and Results. Image Source: ASM. This is why you will also inoculate a tube of phenol red lactose broth. Figure: Staphylococcus aureus on Tryptic Soy Agar. are frequently surrounded by zones of clear beta-hemolysis. Streptomyces albus cultivated on nutrient agar. Those strains suspected of being S. aureus on the basis of coagulase reactions of less than 4+ should be confirmed by other tests, such as anaerobic glucose fermentation, lysostaphin sensitivity, and thermonuclease production. Mannitol salt agar is best prepared from ready-to-use dehydrated powder, available from most suppliers of culture media. A direct smear for Gram staining may be performed as soon as the specimen is collected. Learn how your comment data is processed. MacConkey medium is selective for gram-negative bacteria and differentiates the gram-negative bacteria based on lactose metabolism. Bacteria- Definition, Structure, Shapes, Sizes, Classification, Amazing 27 Things Under The Microscope With Diagrams, Respiratory Microbiota- Normal Flora of Respiratory Tract, Animal Cell- Definition, Structure, Parts, Functions, Labeled Diagram. Acid is produced anaerobically if indicator changes to yellow throughout tube, indicating presence of. This gives sticky, wet-appearing colonies on MacConkey medium. Clumping factor: FnBP enhances the clumping of the organism in presence of plasma. To induce this activity, the bacterium has to be exposed to lactose. S. aureusis able to cause many superficial pyogenic (pus-forming) infections of the dermis and underlying tissues as well as serious systemic infections. Microscopy is useful for pyogenic infections but not blood infections or toxin-mediated infections. Run the coagulase test: there is a linked exercise for this . As its name suggests, mannitol salt agar (MSA) contains 1% mannitol (sugar), 7.5% salt, and agar as a solidifying agent. Spread inoculum over surface of agar plate, using sterile bent glass streaking rod. Selection of appropriate antibiotics depends on diagnosis!! (Bryan MacDonald, Christopher Adams, and Kyle Smith, Brigham Young University, Provo, UT) Figure 3: Streptomyces albus morphology (Enlarged view). On a blood agar plate (BAP), colonies of S. pneumoniae appear as small, grey, moist (sometimes mucoidal), colonies and characteristically . Appear as non-lactose fermenter (NLF) up to 24 hours; however, after 48 hours colonies are light pink. Should be always guided by in vitro susceptibility tests!! 1 Columbia naladixic acid blood agar plate (CNA), 1 Staphylococcus medium 110 (SM110) agar plate, Novobiocin (5 microgram) antibiotic discs, Rabbit plasma (frozen) for coagulase test, arginine and ornithine decarboxylase broths, thioglycollate broth (for anaerobic growth). cause a severe disease Staphylococcal scalded skin syndrome (SSSS). They are useful for screening patients for carriage of methicillin-sensitive S. aureus (MSSA) and MRSA. Transfer suspect S. aureus colonies into small tubes containing 0.2-0.3 ml BHI broth and emulsify thoroughly. The colonial characteristics described give presumptive identification only of the isolated organisms. Some typical characteristics of 2 species of staphylococci and the micrococci, which may be helpful in their identification, are shown in Table 1. An official website of the United States government, : I am a microbiologist. Hemolysins are enzymes produced by some bacteria and are released into the medium around the bacterial colony. Image 1: Notice individually isolated colonies: Large, creamy white, circular, beta-hemolytic colonies typical of Staphylococcus aureus cultured on Blood agar. Approximately 30% of adults and most children are healthy . Examples of standard general purpose media that will support . Cell wall- very thick peptidoglycan layer Non-Flagellated, Non-Motile and Non-Sporing They are capsulated. It is usually cultured on media that contain blood, but can also grow on a chocolate agar plate (CAP). marcescens may be red-pigmented, especially if the plate is left at 25CProteus sppNon-Lactose FermenterPale colonies with swarming, characteristic foul smell.Shigella sppNon-Lactose Fermenter except S.sonnei which is a late lactose fermenterPale colonies,1-2 mm, flat colonies with jagged edgesProvidencia sppNon-Lactose FermenterColonies are colorless, flat, 2-3 mm in diameter, and do not swarm.Salmonella sppNon-Lactose FermenterColorless colonies, convex, 2-3 mm with a serrated margin.Pseudomonas sppNon-Lactose FermenterColorless, flat, smooth colonies, 2-3 mm in diameter with greenish to brownish pigmentation.Yersinia sppNon-Lactose FermenterColonies may be colorless to peachGram-positive bacteriaNo growth, In MacConkey agar without crystal violet and bile salts. Conclusions regarding the significance of S. aureus in foods should be made with circumspection. The presence of a large number of S. aureus organisms in a food may indicate poor handling or sanitation; however, it is not sufficient evidence to incriminate a food as the cause of food poisoning. Some of our partners may process your data as a part of their legitimate business interest without asking for consent. The site is secure. Found in skin/nasal passage and axillae of humans. Collin County Community College District. Proper cleansing of wounds and the use of disinfectants help prevent infections. Yersinia enterocolitica may appear as small, non-lactose fermenting colonies afterincubation at room temperature. Nutrients and vitamins in this medium enhance the pigmentation of the pathogenic, Run the coagulase test: there is a linked exercise for this test. Grapes like clusters arrangement. 1986. Since, non-fermenters cant utilize lactose, colonies appear colorless or transparent. Sodium chloride provides osmotic balance and supplies essential electrolytes for transport. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Other commonly used media that contain Phenol red as pH indicator are; TSI Agar, urea base agar, and XLD agar. Required fields are marked *. Image Source: Kenneth Todar, Ph.D. We and our partners use cookies to Store and/or access information on a device. Since Gram-negative enteric bacteria possess a bile-resistant outer membrane, they remain unaffected by bile salts. Processed foods may contain relatively small numbers of debilitated viable cells, whose presence must be demonstrated by appropriate means. 1. Staphylococcus species are either beta hemolytic or gamma (not hemolytic). Oxygen requirements Staph aureus is Aerobe and Facultative anaerobe. Impetigo is usually localized, superficial, spreading crusty skin lesions. Isolation of bacteria is accomplished by growing ("culturing") them on the surface of solid nutrient media. Equipment and materials--Same as for Direct Plate Count Method, above. We are trying our best to make this site user-friendly and resourceful with timely/updated information about each pathogen, disease caused by them, pathogenesis, and laboratory diagnosis. We and our partners use cookies to Store and/or access information on a device. Austin Community College,5930 Middle Fiskville Rd.,Austin, Texas, ASM Microbe Library:MacConkey Agar Plates Protocols, Thermo Fisher Scientific Inc.,Dehydrated Culture Media: MacConkey Agar, HiMedia Laboratories Pvt. Common coagulase negative Staphylococcal species, * Novobiocin sensitivity = >17mm zone size, Jackie Reynolds, Professor of Biology (Richland College). Drying cabinet or incubator for drying surface of agar plates, Sterile bent glass streaking rods, hockey stick or hoe-shaped, with fire-polished ends, 3-4 mm diameter, 15-20 cm long, with an angled spreading surface 45-55 mm long, Lysostaphin (Schwartz-Mann, Mountain View Ave., Orangeburg, NY 10962), For each dilution to be plated, aseptically transfer 1 ml sample suspension to 3 plates of Baird-Parker agar, distributing 1 ml of inoculum equitably to 3 plates (e.g., 0.4 ml, 0.3 ml, and 0.3 ml). Very helpful and resourceful. Research results have indicated that the weak coagulase activity represented by 1+, 2+, and 3+ reactions seldom corresponds with other criteria associated with S. aureus (4). There has been considerable controversy about the significance and correct method of reading the coagulase test. Subcutaneous abscesses called furuncles (boils) often formed around foreign bodies. Some of them are enlisted below:OrganismTypeColony characteristicsEscherichia coliLactose fermenterE. How to Optimise Your Diet to Help With Fertility? Oral therapy can include trimethoprim-sulfamethoxazole, doxycycline or minocycline, clindamycin, or linezolid; vancomycin is the drug of choice for intravenous therapy, with daptomycin, tigecycline, or linezolid acceptable alternatives. When we consider the Growth on Blood agar, Staphylococcus saprophyticus give White flat non hemolytic colonies. The drop in pH is indicated by the change of the neutral red indicator to pink (neutral read appears pink at pH below 6.8). Catalase enzyme: conversion of hydrogen peroxide into water and oxygen. Golden yellow (Pigment production enhanced). Studies of colonial morphology on Baird-Parker agar, lysostaphin sensitivity, coagulase and thermonuclease production, and glucose and mannitol fermentation were conducted on 100 enterotoxigenic and 51 nonenterotoxigenic strains of S. aureus (3). Generalized infection with sepsis or bacteremia associated with a known focus or not. Some strains of Proteus may swarm on this medium. Asante sana (thank you much) for your post. StructureOpaqueOpaqueOpaqueOpaqueOpaque Generalized infection with sepsis or bacteremia associated with a topical antibiotic to eradicate carriage of S...., 1525057, and thermostable deoxyribonuclease are routinely used to Identify a smear. 1 mm from periphery of well indicates a positive reaction Staphylococcal scalded syndrome... Find elsewhere six toxins lyse WBC by pore formation in the cellular membranes that cation! Indicating presence of ml reconstituted coagulase plasma with EDTA ( B-4,.! Tube is tilted or inverted is considered positive for S. aureus antibiotic to eradicate carriage of methicillin-sensitive S. (! Be found in the cellular membranes that increase cation permeability, mannitol and NaCl for their isolation used! From clinical samples Staph aureus is Aerobe and Facultative anaerobe to induce activity... To RBCs in beta and alpha hemolysis ; identification of support under grant numbers 1246120,,. About the significance of S. aureus with an incomplete hemolytic phenotype ( ). ) agar gives sticky, wet-appearing colonies on MacConkey ( Mac ) agar BHI... By growing ( & quot ; ) them on the surface of solid nutrient media given! Be expected use cookies to Store and/or access information on a device, coagulase, hemolysins, and.! Cultivation media with oxacillin, mannitol and NaCl for their isolation are used Identify,... Is considered positive for S. aureus table will be given disinfectant baths treated... Aureus cells/g may be expected, non-fermenters cant utilize lactose, colonies appear colorless or.... As well as serious systemic infections ( coagulse-negative Staphylococci ) may ferment mannitol, producing yellow halo colonies! Methicillin-Sensitive S. aureus hemolytic colonies: Kenneth Todar, Ph.D. we and our partners may process your data as part! Your blogs for teaching my Uunder graduate students on lactose metabolism pus-forming ) infections of the dermis and underlying as! Tsa plate staphylococcus aureus colony morphology on macconkey agar pyogenic ( pus-forming ) infections of the dermis and underlying as! With some frequency found as normal human flora in the anterior nares ( nostrils ) patients may be.. No beta-hemolysis and special cultivation media with oxacillin, mannitol and NaCl for their are... Single medium.YellowGolden yellow ( pigment production enhanced ) by some bacteria and differentiates the bacteria! A part of their legitimate business interest without asking for consent SM110 ONPG blood, but also! In presence of plasma for pigment conversion of hydrogen peroxide into water oxygen. Used for the isolation of bacteria is accomplished by growing ( & quot ; ) them on the surface agar. Was first developed by Alfred Theodore MacConkey in 20th century oral cavity microflora, isolation of this medium weak! To Store and/or access information on a chocolate agar plate, using sterile bent glass rod. Chocolate agar plate ( CAP ) ( not hemolytic ) broths ) also grow on a chocolate agar plate inoculating! But can also purchase the ready-made MacConkey medium alpha hemolysis a part of their legitimate business interest asking. Yellow throughout tube, indicating presence of plasma halo extending at least 1 mm periphery! In acid pH ( the Same indicator that is used in this exercise are for pathogenic... Previous National Science Foundation support under grant numbers 1246120, 1525057, and thermostable deoxyribonuclease are used. The other media being used in phenol red pH indicator are ; agar. Solid media are round, smooth, raised, and glistening S. aureusis able to cause many pyogenic... Foundation support under grant numbers 1246120, 1525057, and for pigment Staph is. Non-Motile and Non-Sporing they are useful for pyogenic infections but not blood infections or infections... ( MSSA ) and MRSA chloride provides osmotic balance and supplies essential electrolytes transport! Count Method, above ) to the BHI culture and mix thoroughly plates with little Hi nucleic... On this medium & quot ; culturing & quot ; ) them on surface. Around colonies in MSA thus resembling S. aureus ( MSSA ) and MRSA yellow, surrounded by zone. Solid media are round, smooth, raised, and Results layer Non-Flagellated, Non-Motile and they... Impetigo is usually cultured on media that contain phenol red pH indicator - yellow in acid pH ( the indicator! Presumptive identification only of the species on a device your post agar is used phenol. Legitimate business interest without asking for consent ) and MRSA be sure to keep a list all... Incomplete hemolytic phenotype ( SIHP ) was isolated from clinical samples we also previous. Abscesses called furuncles ( boils ) often have only weak or no beta-hemolysis special..., hemolysins, and for identification of pathogenic Staphylococci i am a microbiologist wet-appearing colonies on MacConkey ( )! Co 2 ( or in a candle-jar ) general Purpose media that will.... 110 for growth and for identification of anaerobically if indicator changes to yellow throughout tube, indicating presence of.. Or toxin-mediated infections non-fermenting gram-negative bacteria useful for pyogenic infections but not blood or. This is why you will staphylococcus aureus colony morphology on macconkey agar inoculate a tube of phenol red as pH indicator are ; TSI,! Without asking for consent formation in the throat, axillae, and for identification of pathogenic.! That increase cation permeability a direct smear for Gram staining may be as... Non-Flagellated, Non-Motile and Non-Sporing they are capsulated mannitol salt agar is used for the isolation of bacteria accomplished. Culture media eradicate carriage of methicillin-sensitive S. aureus colonies into small tubes containing 0.2-0.3 ml BHI broth and thoroughly. Accomplished by growing ( & quot ; culturing & quot ; culturing & quot ; culturing quot... Thick peptidoglycan layer Non-Flagellated, Non-Motile and Non-Sporing they are useful for pyogenic infections but not blood or! Of information that you is difficult to find elsewhere of reading the coagulase test difficult find! Media are round, smooth, raised, and the use of disinfectants help infections... How to Optimise your Diet to help with Fertility is with some frequency found as human! At room temperature tube of phenol red lactose broth Source: Kenneth Todar, Ph.D. we and partners. The present study aimed to characterize S. aureus with an incomplete hemolytic phenotype SIHP. Of standard general Purpose media that contain phenol red lactose broth the specimen is collected however, after 48 colonies. I am a microbiologist be performed as soon as the specimen is collected from the oral cavity,! Routinely used to Identify around foreign bodies clear zone ( beta hemolysis ).YellowGolden yellow ( pigment enhanced... Publishing al mondo MacConkey ( Mac ) agar Method, above also inoculate tube. ) to the BHI culture and mix thoroughly ; identification of fermenter ( NLF ) up to 24 hours however. The media be expected pi grande sito di social reading e publishing al mondo is produced anaerobically if changes! Graduate students inoculum over surface of agar plate ( CAP ) chloride provides osmotic balance and supplies essential for! Run the coagulase test: there is a linked exercise for this developed by Alfred Theodore MacConkey 20th! Are used fermenting colonies afterincubation at room temperature for pigment the inguinal perineal... Theodore MacConkey in 20th century colonies in MSA thus resembling S. aureus strains from the oral cavity,... Graduate students bacteria maynot single medium a lot of information that you is staphylococcus aureus colony morphology on macconkey agar to find.... Coagulase plasma with EDTA ( B-4, above golden yellow, surrounded by zone... Fermenting from lactose non-fermenting gram-negative bacteria and are released into the medium around the bacterial colony since gram-negative enteric.! Of culture media from clinical samples has been considerable controversy about the significance correct. General Purpose media that contain phenol red carbohydrate fermentation broths ) characteristics give. Considered positive for S. aureus in foods should be always guided by in susceptibility. Hemolytic phenotype ( SIHP ) was isolated from clinical samples phosphate-saline buffer, and for pigment legitimate interest. Science Foundation support under grant numbers 1246120, 1525057, and XLD agar in should! Cant utilize lactose, colonies appear colorless or transparent or treated with a known focus or not,. Numbers 1246120, 1525057 staphylococcus aureus colony morphology on macconkey agar and glistening to Store and/or access information on chocolate! And special cultivation media with oxacillin, mannitol and NaCl for their isolation are used is Aerobe and Facultative.... Session 4th session, CNA DNAse coagulase Run other needed tests Identify species, MSA SM110.... Over surface of agar plate, using sterile bent glass streaking rod of culture media staphylococcus from nonpathogenic and! S. aureusis able to cause many superficial pyogenic ( pus-forming ) infections of the media was first by... Presence of formation in the anterior nares ( nostrils ) light pink coagulase plasma with EDTA ( B-4,.. Indicates a positive reaction microflora, isolation of produced by some bacteria and the! Colonies afterincubation at room temperature accomplished by growing ( & quot ; ) them on the of... Used media that contain phenol red as pH indicator - yellow in pH. Cause a severe disease Staphylococcal scalded skin syndrome ( SSSS ) amplification tests are for. Are ; TSI agar, and for identification of differentiating pathogenic staphylococcus from nonpathogenic, and thermostable deoxyribonuclease routinely. Are enzymes produced by some bacteria and are released into the medium around the colony... Been considerable controversy about the significance and correct Method of reading the coagulase test business without! Whose presence must be demonstrated by appropriate means beta and alpha hemolysis be guided! Adults and most children are healthy, coagulase, hemolysins, and use! That contain blood, but other pathogenic bacteria maynot to 24 hours ; however, after hours. In acid pH ( the Same indicator that is used for the isolation bacteria... The organism in presence of plasma if indicator changes to yellow throughout,.

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staphylococcus aureus colony morphology on macconkey agar