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Figure 1: Citrate test Citrobacter freundii and Escherichia coli. FIG. 1. A positive citrate test result given by Citrobacter freundii (left) is indicated by growth and a blue color change. A negative citrate test result given by Escherichia coli (right) is indicated by a lack of growth and no color change. (Mary G. Miller, Southeastern Louisiana University, Hammond)

Figure 2: Citrate test on Klebsiella pneumoniae and Escherichia coli. FIG. 2. A positive citrate test result given by Klebsiella pneumoniae in the positive control (tube 1) and the test (tube 2) is indicated by growth and a blue color change. A negative citrate test result given by Escherichia coli in the negative control (tube 3) is indicated by a lack of growth and no color change. (Shashidhar Vishwanath, Kasturba Medical College, Karnataka, India)

Figure 3: Citrate test on Escherichia coli and Enterobacter aerogenes. FIG. 3. A negative citrate test result given by Escherichia coli (left) is indicated by a lack of growth and no color change. A positive result given by Enterobacter aerogenes (right) is indicated by growth and a blue color change. (Tasha L Sturm, Cabrillo College, Aptos, CA)

Figure 4: Uninoculated citrate test. FIG. 4. Uninoculated citrate slant. The green color indicates that the medium pH is between 6.9 and 7.6. (Maria P. MacWilliams, University of Wisconsin—Parkside, Kenosha)

Figure 5: Positive citrate test. FIG. 5. This image depicts a positive citrate test. Note the blue color of the medium and the faint white layer of growth on the slant surface. (Maria P. MacWilliams, University of Wisconsin—Parkside, Kenosha)

Figure 6: Citrate test on Proteus mirabilis and Klebsiella pneumoniae. FIG. 6. A negative citrate test result given by Proteus mirabilis (left) is indicated by a lack of growth and no color change. A positive result given by Klebsiella pneumoniae (right) is indicated by growth and a blue color change. An uninoculated tube is also shown. The image depicts the results after a 30-hour incubation. (Jackie Peltier Horn, Houston Baptist University, Houston, TX)

Figure 7: Citrate test on Proteus mirabilis and Klebsiella pneumoniae. FIG. 7. A negative citrate test result given by Proteus mirabilis (left) is indicated by a lack of growth and no color change. A positive result given by Klebsiella pneumoniae (right) is indicated by growth and a blue color change. An uninoculated tube is also shown. The image depicts the results after a 30-hour incubation. (Jackie Peltier Horn, Houston Baptist University, Houston, TX)

Figure 8: Citrate test on Escherichia coli. FIG. 8. The negative result of a citrate test done on Escherichia coli after a 24-hour incubation at 37°C. A negative result is indicated by a lack of growth and no color change. (Anne Hanson, University of Maine, Orono)

Figure 9: Citrate test on Enterobacter aerogenes. FIG. 9. The positive result of a citrate test done on Enterobacter aerogenes after a 24-hour incubation at 37°C. A positive result is indicated by growth and a blue color change. (Anne Hanson, University of Maine, Orono)

Figure 10: Citrate test on Escherichia coli and Enterobacter aerogenes. FIG. 10. The image depicts the results of a citrate test after a 24-hour incubation at 37°C. Tube A shows a negative result given by Escherichia coli which is indicated by a lack of growth and no color change. Tube B shows a positive result given by Enterobacter aerogenes which is indicated by growth and a blue color change. (Anne Hanson, University of Maine, Orono)