Question

Make a Dichotomous Key using the folowing bacteria to ultimately isolate the following organims using PEA, gram stain, catalase test, oxidase test, MSA, etc.:

Proteus                           Acinetobacter                       Staphylococcus                     Micrococcus

Lactobacillus                  Salmonella                            Escherichia                            Neisseria

Bacillus                          Shingella                               Klebsiella                              Citrobacter

Serratia                           Enterobacter                         Pseudomonas                        Streptococcus

Answer 1

Bacteria	PEA	Gram Stain	Catalase Test	Oxidase Test
Proteus	Inhibits the growth	Negative	Positive	Negative
Lactobacilllus	Promotes the growth	Positive	Negative	Negative
Bacillus	Promotes the growth	Positive	Positive	Negative
Serratia	Inhibits the growth	Negative	Positive	Negative
Acinetobacter	Inhibits the growth	Negative	Positive	Negative
Salmonella	Inhibits the growth	Negative	Positive	Negative
Shingella	Inhibits the growth	Negative	Positive	Negative
Enterobacter	Inhibits the growth	Negative	Positive	Negative
Staphylococcus	Promotes the growth	Positive	Positive	Negative
Escherichia	Inhibits the growth	Negative	Positive	Negative
Klebsiella	Inhibits the growth	Negative	Positive	Negative
Pseudomonas	Inhibits the growth	Negative	Positive	Negative
Micrococcus	Promotes the growth	Positive	Positive	Positive
Neisseria	Inhibits the growth	Negative	Positive	Positive
Citrobacter	Inhibits the growth	Negative	Positive	Negative
Streptococcus	Promotes the growth	Positive	Negative	Negative

PEA Test – Phenylethyl alcohol agar (PEA) is a selective medium test which is specific for gram positive bacteria. The selective medium inhibits the growth of gram negative bacteria and promotes growth of gram positive ones.