Description
| Intended Use and Principle of Procedure |
| MacConkey Broth is used for cultivating gram-negative, lactose-fermenting bacilli in water and foods as a presumptive test for coliform organisms.
Peptone provides amino acids and other growth factors. Lactose is a carbon energy source for gram-negative lactosefermenting bacilli. Oxgall inhibits the growth of grampositive organisms. Bromcresol purple is the indicator. |
| Summary and Explanation |
| MacConkey Broth is a modification of the original bile salt broth recommended by MacConkey that contained 0.5% sodium taurocholate and litmus as an indicator. In later publications, MacConkey suggested variations of this formulation using neutral red indicator instead of litmus. Childs and Allen demonstrated the inhibitory effect of neutral red and substituted the less inhibitory bromcresol purple. Oxgall in the medium replaces the original sodium taurocholate to inhibit growth of gram-positive organisms. |
| Formulae | ||||||||
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| Procedure |
| Inoculate tubes with the test specimen. Incubate tubes for 18-24 hours at 35 ± 2°C in an aerobic atmosphere. |
| Directions for Preparation from Dehydrated Product |
| 1. Dissolve 35 g of the powder in 1 L of purified water. For testing 10 mL samples, prepare double strength. 2. Dispense in test tubes containing Durham tubes. 3. Autoclave at 121°C for 15 minutes. 4. Test samples of the finished product for performance using stable, typical control cultures.
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| Identification Specification and Cultural Response | ||||||||||||||||||||||||||||
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| Expected Results |
| Lactose-fermenting organisms grow very well in MacConkey Broth and produce acid, causing the medium to turn yellow. Gas is also produced, which collects in the Durham tubes. Nonfermenting organisms produce good growth but will not produce acid or gas. |
| References |
| 1. MacConkey. 1901. Zentralbl. Bakteriol. 29:740. 2. MacConkey. 1905. J. Hyg. 5:333. 3. MacConkey. 1908. J. Hyg. 8:322. 4. Childs and Allen. 1953. J. Hyg. Camb. 51:468 |
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