Chp. 9 Self-Test Question

What are the three traditional identification methods for microbes?

Colony morphology characterization, microscopic morphology, and biochemical testing.

What is the most important carbohydrate utilization test for differentiating gram-negative rods?

Lactose utilization.

What does a K/K (red slant/red butt) TSI reaction indicate?

No fermentation of lactose, glucose, or sucrose; typically not a member of the Enterobacteriaceae group.

What does a K/A (red slant/yellow butt) TSI reaction indicate?

Glucose fermentation only.

What does an A/A (yellow slant/yellow butt) TSI reaction indicate?

Fermentation of lactose, sucrose, or both, in addition to glucose.

What does a black butt in TSI indicate?

H2S production.

What enzyme do delayed lactose fermenters lack?

β-galactoside permease (transport enzyme).

What enzyme do delayed lactose fermenters possess?

β-galactosidase (cleaving enzyme).

What is the ONPG test used for?

To determine if an organism is a delayed lactose fermenter (dLF) or a non-lactose fermenter (NLF).

What color indicates a positive ONPG test?

Yellow.

What is the key takeaway about MR and VP?

A culture will only be positive for one pathway (MR+ or VP+), never both.

What is the purpose of the decarboxylase test?

To determine whether a bacterial species possesses enzymes capable of decarboxylating specific amino acids.

What color indicates a positive decarboxylase test?

Purple.

What color indicates a positive phenylalanine deaminase test?

Green.

What color change indicates a positive citrate utilization test?

Green to blue.

What color indicates a positive indole test?

Red (Ehrlich or Kovac's); blue/green (spot indole).

What color indicates a positive oxidase test?

Lavender.

What color indicates a positive urease test?

Bright pink.

What is the purpose of the API 20E system?

To identify gram-negative fermentative bacteria (Enterobacteriaceae).

How many digits are in the API 20E profile number?

Seven digits.

How is each digit of the API 20E profile number calculated?

Positive first test = 1, positive second test = 2, positive third test = 4; add the three scores in each group.

What is the purpose of mineral oil in some API 20E tests?

To create anaerobic conditions.

What additional test is performed outside the API 20E strip?

Oxidase test (counts as the 21st test).

What newer identification approaches are increasingly used in place of biochemical systems?

Protein profiling (MALDI) and sequencing.