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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° BBHC. (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° BBHC. (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
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