FIG. 1. Eosin-methylene blue (EMB) agar plate inoculated with Escherichia coli (a gram-negative coliform bacterium) showing good growth of dark blue-black colonies with metallic green sheen indicating vigorous fermentation of lactose and acid production which precipitates the green metallic pigment. (Naowarat Cheeptham, Thompson Rivers University, Kamloops, BC, Canada)
FIG. 2. EMB agar plate inoculated with Enterobacter aerogenes (a gram-negative coliform bacterium) showing good growth of brown, dark-centered, mucoid colonies indicating lactose fermentation and acid production. (Naowarat Cheeptham, Thompson Rivers University, Kamloops, BC, Canada)
FIG. 3. EMB agar plate inoculated with Klebsiella pneumoniae (a gram-negative coliform bacterium) showing good growth of brown, dark-centered, mucoid colonies (smaller than Enterobacter) indicating lactose fermentation and acid production. (Naowarat Cheeptham, Thompson Rivers University, Kamloops, BC, Canada)
FIG. 4. EMB agar plate inoculated with Pseudomonas aeruginosa (a gram-negative noncoliform bacterium) showing good growth but no fermentation of sugars or acid production. (Naowarat Cheeptham and Carolynne Fardy, Thompson Rivers University, Kamloops, BC, Canada)
FIG. 5. EMB agar plate inoculated with Proteus vulgaris (a gram-negative coliform bacterium) showing growth of pink colonies indicating non-lactose fermentation and some acid production. (Naowarat Cheeptham, Thompson Rivers University, Kamloops, BC, Canada)
FIG. 6. EMB agar plate inoculated with a mixed culture of Escherichia coli and Pseudomonas aeruginosa. Note the metallic green sheen of the strong lactose-fermenting Escherichia coli and the pinkish colonies of nonfermenter Pseudomonas aeruginosa. (Archana Lal, Independence Community College, Independence, KS)
FIG. 7. EMB agar plate inoculated with Acinetobacter baumannii (a gram-negative non-glucose-fermenting bacillus) showing a colony with a classic blue-grey center. This should not be mistaken for evidence of lactose fermentation on EMB agar. (Bobbi Pritt, Mayo Clinic, Rochester, MN)
FIG. 8. EMB agar plate inoculated with Stenotrophomonas maltophilia (a gram-negative non-glucose-fermenting bacillus) showing good growth and non-lactose-fermenting morphology. (Bobbi Pritt, Mayo Clinic, Rochester, MN)
FIG. 9. EMB agar plate inoculated with mixed enteric flora. The lactose fermenter Escherichia coli grew with purple-centered colonies while the lactose nonfermenter Salmonella enteritidis grew as colorless colonies. Salmonella enteritidis mixed with Escherichia coli is able to utilize the acid products as energy source, resulting in an insufficient acid buildup to precipitate out the Eosin Methylene Blue and no green metallic sheen is produced by Escherichia coli. (Jerry Keplinger, East Tennessee State University, Johnson City)
FIG. 10. EMB agar plate inoculated with Clostridium perfringens (a gram-positive bacterium) maintained under anaerobic conditions and showing no growth. (Naowarat Cheeptham, Thompson Rivers University, Kamloops, BC, Canada)
FIG. 11. EMB agar plate inoculated with Bacillus subtilis (a gram-positive bacterium) showing poor growth. (Naowarat Cheeptham, Thompson Rivers University, Kamloops, BC, Canada)
FIG. 12. EMB agar plate inoculated with Micrococcus luteus (a gram-positive bacterium) showing no growth. (Naowarat Cheeptham, Thompson Rivers University, Kamloops, BC, Canada)
FIG. 13. EMB agar plate inoculated with Staphylococcus aureus (a gram-positive bacterium) showing no growth. (Archana Lal, Independence Community College, Independence, KS)
FIG. 14. EMB agar plate inoculated with Streptococcus group B (a gram-positive bacterium) showing no growth. (Archana Lal, Independence Community College, Independence, KS)
FIG. 15. EMB agar plate inoculated with (A) Escherichia coli, (B) Bacillus subtilis, (C) Pseudomonas aeruginosa, and (D) Staphylococcus aureus. The two gram-positive bacteria Bacillus subtilis and Staphylococcus aureus did not grow, while the two gram-negative bacteria Escherischia coli and Pseudomonas aeruginosa grew with typical lactose fermenter (colonies with green metallic sheen) and nonfermenter (pink colonies) morphology. (Archana Lal, Independence Community College, Independence, KS)
FIG. 16. EMB agar plate inoculated with Salmonella enteritidis (a gram-negative coliform bacterium) showing good growth of grey mucoid colonies with no fermentation of lactose or acid production. (Naowarat Cheeptham and Carolynne Fardy, Thompson Rivers University, Kamloops, BC, Canada)
FIG. 17. EMB agar plate inoculated with (A) Escherichia coli, (B) Pseudomonas aeruginosa, (C) Klebsiella pneumoinae, and (D) Enterobacter aerogenes. All four gram negative bacteria grew exhibiting different morphology. Escherischia coli grew with typical lactose fermenter morphology with excessive acid production and precipitation of green metallic pigment (colonies with green metallic sheen). Pseudomonas aeruginosa grew exhibiting the nonfermenter morphology (pinkish colonies), both Klebsiella pneumoniae and Enterobacter aerogenes grew with lactose fermentation and acid production morphology (with purple dark centered mucoid colonies). (Naowarat Cheeptham and Carolynne Fardy, Thompson Rivers University, Kamloops, BC, Canada)
PROTOCOL
The protocol for utilizing EMB agar in undergraduate education is available via a subscription to the MicrobeLibrary.
If you are already a MicrobeLibrary subscriber and logged in, please visit Eosin-Methylene Blue Protocol.
Also available in the Curriculum Collection (requires subscription):
Antibiotic Susceptibility of E. coli Isolates
Also available in the Visual Collection:
Lactose Nonfermenter on EMB
REVIEWERS
This resource was peer-reviewed at the ASM Conference for Undergraduate Educators 2007.
Joel Adams-Stryker
Evergreen Valley College, San Jose, CA
Robert Bauman
Amarillo College, Amarillo, TX
Dexter Beck
Chattahoochee Technical College, Marietta, GA
Donald Breakwell
Brigham Young University, Provo, UT
Elaine Bukowski
Ivy Tech Community College of Indiana, Prospect, KY
Cheryl Dias
Harold Washington College, Chicago, IL
Edith Hillard
Frederick Community College, Frederick, MD
Catherine A. Hopper
University of Maine, Orono, ME
Joanna Klein
Northwestern College, St. Paul, MN
Alexandra Kurtz
Georgia Gwinnett College, Lawrenceville, GA
Sue Merkel
Cornell University, Ithaca, NY
Heidi R. Smith
FRONT Range Community College, Fort Collins, CO
Sherry Stewart
Navarro College, Corsicana, TX
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