Interpretation
Organisms growing on Simmons Citrate Agar are capable of using citrate as the sole carbon source and they can metabolize the ammonium salt in the medium.
Use of citrate increases the pH of the medium. The increase in pH then causes color change in the bromothymol blue indicator, turning it blue. Under acidic condition it changes to yellow color. This color change is useful because growth on Simmons Citrate Agar is often limited and would be hard to observe if it were not for the color change.
Sometimes, it is possible to detect growth on the Simmons Citrate Agar without the accompanying color change to blue. This is most likely due to insufficient incubation. Either a combination of blue color and growth or growth alone without the blue color should be scored as a positive for the citrate use test.
Growth media / agar plates
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Selective media |
Gram positive
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Actinobacteria
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Mycobacterium tuberculosis (Lowenstein-Jensen medium, Middlebrook 7H9 Broth, Middlebrook 7H10 Agar, Middlebrook 7H11 Agar) · Mycoplasma pneumoniae (Eaton's agar)
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Firmicutes
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Corynebacterium diphtheriae (Hoyle's agar) · Enterococcus (Bile esculin agar) · Lactobacillus (MRS agar) · Lactococcus (M17 agar) · Staphylococcus (Mannitol salt agar)
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Gram negative
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Alphaproteobacteria
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Brucella abortus (Brucella agar)
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Betaproteobacteria
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Neisseria (Thayer-Martin agar)
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Gammaproteobacteria
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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)
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Differential media |
Lactose fermenting gram negative (MacConkey agar/Sorbitol-MacConkey agar, Eosin methylene blue) · Hektoen enteric agar · sulfur (Bismuth sulfite agar)
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Fungal media |
Dermatophyte test medium · Potato dextrose agar · Sabouraud agar
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Nonselective media |
Chocolate agar · Nutrient agar · Plate count agar
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Other/ungrouped media |
Cysteine lactose electrolyte deficient agar · Cystine tryptic agar · Endo agar · LIA slant · Müller-Hinton agar/PNP agar · R2a agar · Simmons' citrate agar · Trypticase soy agar · TSI agar
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M: BAC
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bact (clas)
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gr+f/gr+a (t)/gr-p (c)/gr-o
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drug (J1p, w, n, m, vacc)
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