FIG. 1. Uninoculated MacConkey agar plate. (David Miller and Patrick Hanley, Hartwick College)
FIG. 2. MacConkey agar plate inoculated with the gram-negative lactose fermenter Escherichia coli and the gram-negative non-lactose fermenter Serratia marcescens. (David Miller and Patrick Hanley, Hartwick College)
FIG. 3. MacConkey agar plate inoculated with Escherichia coli using the streak plate technique. (David Miller and Patrick Hanley, Hartwick College)
FIG. 4. MacConkey agar plate inoculated with Escherichia coli using the streak plate technique. (Anne Y. Tsang, University of Maryland)
FIG. 5. MacConkey agar plate inoculated with Escherichia coli. (David Miller and Patrick Hanley, Hartwick College)
FIG. 6. MacConkey agar plate inoculated with the gram-negative lactose non-fermenter Serratia marcescens and Escherichia coli using the streak plate technique. (David Miller and Patrick Hanley, Hartwick College)
FIG. 7. MacConkey agar plate inoculated with Serratia marcescens and Escherichia coli using the streak plate technique. (David Miller and Patrick Hanley, Hartwick College)
FIG. 8. MacConkey agar plate inoculated with Escherichia coli and Salmonella typhimurium using the streak plate technique. (Anne Y. Tsang, University of Maryland)
FIG. 9. MacConkey agar plate inoculated with the gram-negative lactose fermenter Klebsiella pneumoniae using the streak plate technique. (Mary Allen, Hartwick College)
FIG. 10. MacConkey agar plate inoculated with the gram-negative lactose fermenter Citrobacter using the streak plate technique (Mary Allen, Hartwick College)
FIG. 11. MacConkey agar plate inoculated with Serratia marcescens, Escherichia coli (showing the pink halo) and the weak lactose fermenter Enterobacter aerogenes. (Mary Allen, Hartwick College)
FIG. 12. MacConkey agar plate inoculated with the delayed lactose fermenter Shigella sonnei (light pink growth), Serratia marcescens, and Escherichia coli (showing the pink halo). (Mary Allen, Hartwick College)
FIG. 13. MacConkey agar plate inoculated with the delayed lactose fermenter Shigella sonnei (light pink growth), Serratia marcescens, and Escherichia coli (showing the pink halo). (Mary Allen, Hartwick College)
FIG. 14. MacConkey agar plate inoculated with Escherichia coli (red) and Enterobacter aerogenes (pink) using the streak plate technique. (Mary Allen, Hartwick College)
FIG. 15. MacConkey agar plate inoculated with Escherichia coli (red) and Klebsiella pneumoniae (pink) using the streak plate technique. (Mary Allen, Hartwick College)
FIG. 16. MacConkey agar plate inoculated with Escherichia coli (red) and Klebsiella pneumoniae (pink) using the streak plate technique. (Mary Allen, Hartwick College)
FIG. 17. Burkholderia cepacia grows as tiny pinpoints on MacConkey agar in 24 hours at 37°C. (Rebecca Buxton, University of Utah)
FIG. 18. Same plate as FIG. 17 at 48 hours, Burkholderia cepacia displays small non-lactose fermenting colonies. Some strains appear somewhat purple due to strong lactose oxidation. (Rebecca Buxton, University of Utah)
FIG. 19. Stenotrophomonas maltophilia grows as tiny pinpoints on MacConkey agar in 24 hours at 37°C. (Rebecca Buxton, University of Utah)
FIG. 20. Same plate as FIG. 19 at 48 hours, Stenotrophomonas has distinct non-lactose fermenting colonies. The indicator has turned an alkaline tan color. (Rebecca Buxton, University of Utah)
FIG. 21. Typical spreading non-lactose fermenting colonies of Pseudomonas aeruginosa. The heavy growth in the primary innoculum has begun to display a blue-green pigment. (Rebecca Buxton, University of Utah)
FIG. 22. Although Acinetobacter baumanii is incapable of fermentation, its very strong lactose oxidation leads to weakly acid/purple colonies on MacConkey agar. (Rebecca Buxton, University of Utah)
FIG. 23. An encapsulated strain of Pseudomonas aeruginosa recovered from a cystic fibrosis patient at 24 hours. (Rebecca Buxton, University of Utah)
FIG. 24. Same plate as FIG. 23 at 48 hours, this strain of Pseudomonas aeruginosa make abundant, mucoid capsular material. (Rebecca Buxton, University of Utah)
FIG. 25. Normal fecal flora mixed with Salmonella. This unusual Salmonella strain ferments lactose. (The colonies were distinguished by producing abundant H2S on Hektoen Agar). (Rebecca Buxton, University of Utah)
FIG. 26. Normal fecal flora (lactose fermenters) mixed with Shigella sonnei (non-lactose fermenter). (Rebecca Buxton, University of Utah)
FIG. 27. This appears to be a pure culture of E.coli. (The patient was suffering from significant diarrhea due to Campylobacter jejuni, which doesn't grow on MacConkey agar). (Rebecca Buxton, University of Utah)
FIG. 28. On very close observation, the tiny pinpoints of a Vibrio species are visible among the large, normal fecal lactose fermenters. On Thiosulfate Citrate Bile Sucrose (TCBS) agar, this sample grew yellow, sucrose-fermenting colonies of V. alginolyticus. (Rebecca Buxton, University of Utah)
FIG. 29. Example of mixed fecal flora at 24 hours. One colony type of lactose fermentor and two of non-lactose fermentors, none of which were identified as typical causes of gastroenteritis. (Rebecca Buxton, University of Utah)
FIG. 30. Same plate as FIG. 29 at 48 hours. (Rebecca Buxton, University of Utah)
FIG. 31. Red-pigmented Serratia marcescens. Students often mistake the red pigment for lactose fermentation. (Rebecca Buxton, University of Utah)
FIG. 32. Klebsiella pneumoniae: Mucoid, lactose-fermenting colonies are typical of Klebsiella and Enterobacter species. (Rebecca Buxton, University of Utah)
FIG. 33. Proteus vulgaris: Non-lactose fermenters with slight swarming. (Rebecca Buxton, University of Utah)
PROTOCOL
The protocol for utilizing the MacConkey Agar in undergraduate education is available via a subscription to the MicrobeLibrary.
If you are already a MicrobeLibrary subscriber and logged in, please visit MacConkey Agar Protocols.
REVIEWERS
This resource was peer-reviewed at ASM Conference for Undergraduate Education 2005 (ASMCUE, 2005).
Participating Reviewers:
Anne Hanson University of Maine, Orono
Donald Lehman
University of Delaware, Newark
Jay Mellies
Reed College, Portland, Ore.
Patricia Shields
University of Maryland, College Park
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