Identifying Gram Negative Bacteria

Identifying Gram Negative Bacteria

Gram Negatives used in Microbiology Lab at PGCC

• The following are Gram Negative bacteria we use as unknowns at PGCC.

• The following slides will give you the most important characteristics of each species and tests for identification.

Escherichia coli

• Gram negative rod - coliform

• Ferments acid and gas from glucose

• Ferments acid and gas from lactose

• Indole positive

• Methyl red positive

• Vogues=Proskauer negative

• Citrate negative

Enterobacter aerogenes

• Gram negative rod - coliform

• Ferments acid and gas from glucose

• Ferments acid and gas from lactose

• Indole negative

• Methyl red negative

• Voges-Proskauer positive

• Citrate positive

Serratia marcescens

• Gram negative rod (bacillus) - non-coliform

• Ferments acid and gas from glucose

• Does not ferment lactose

• DNase positive

• Growth in bile salts, esculin positive

• Produces prodigiosin at 30 degrees, but not at 37 degrees

Salmonella enterica

• Gram negative rod

• Ferments acid and gas from glucose

• Does not ferment lactose

• Growth in bile salts, esculin negative

Pseudomonas fluorescens

• Gram negative rod - non-coliform

• Does not ferment carbohydrates

• Oxidase positive

Neisseria sicca

• Gram negative diplococcus

• Oxidase positive

Multiple Choice

Which of the following is a coccus?

• Neisseria sicca

• Pseudomonas fluorescens

• Escherichia coli

• Serratia marcescens

Multiple Choice

__________ is the only species in our lab which does not ferment carbohydrates.

• Salmonella enterica

• Escherichia coli

• Neisseria sicca

• Pseudomonas fluorescens

Multiple Choice

Non-coliforms lack the ability to ferment

• lactose

• sucrose

• glucose

• carbohydrates