Micro Lab 9 - Gram‐Negative Bacteria And Unknowns

Front 1

Phenol red is a pH indicator that detects acid‐production, while the durham tube detects gas
production. Both of these products (acid and gas)
are due to the fermentation of sugars in the
media.

Back 1

In the carbohydrate fermentation test, what is the function of phenol red and the small inverted (durham) tube, and what process does this indicate?

Front 2

The pH indicator, bromothymol blue, turns from green to blue in an alkaline environment.

Back 2

In the citrate utilization test, what pH indicator is used to detect citrate use, and what color
does this indicator become in alkaline conditions (a positive result)?

Front 3

The pH indicator, brom cresol purple, turns from yellow to purple in an alkaline environment.

Back 3

In the amino acid decarboxylase test, what pH indicator is used to detect decarboxylase
activity, and what color does this indicator become in alkaline conditions (a positive result)?

Front 4

The pH indicator, phenol red, turns from orange to bright pink in an alkaline environment.

Back 4

In the urea hydrolysis test, what pH indicator is used to detect urease activity, and what color
does this indicator become in alkaline conditions (a positive result)?

Front 5

Sulfide
Indole
Motility

Back 5

In the SIM test, what do the three letters represent
(S, I, M), and how does each positive result appear?

Front 6

a by‐product resulting from the breakdown of cysteine, combines with ferrous ions in the growth media to yield a black precipitate.

Back 6

Sulfide

Front 7

a by‐product resulting from the breakdown of tryptophan, reacts with Kovac’s
reagent to yield a red solution

Back 7

Indole

Front 8

Motile bacteria will produce a diffuse cloud of growth extending from a stab in
semisolid agar

Back 8

Motility

Front 9

While macroscopic and microscopic characteristics provide important identification criteria, there can be many similarities and inconsistencies between microorganisms. By determining which enzymes are present, unknown microorganisms can be differentiated and identified through the presence or absence of specific biochemical reactions.

Back 9

Why are biochemical lab tests so important to microbiologists?

Front 10

A sample from the zone inhibition can be inoculated into nutrient broth. If bacteria grow in the broth,
the action of the antibiotic was bacteriostatic not bacteriocidal.

Back 10

How would you tell if the action of an antibiotic 
is bactericidal or bacteriostatic?

Front 11

Bacillus and Clostridium species both form
highly‐resistant spores.

Back 11

Why are Bacillus and Clostridium species considered 
more potentially resistant to disinfectants 
and antiseptics?

Front 12

Hydrogen peroxide breaks down to form water
and oxygen, and oxygen is toxic to anaerobes.

Back 12

What is it about hydrogen peroxide that makes 
it effective in controlling the growth of  vegetative anaerobes?

Front 13

Bacterial spores

Back 13

What would a chemical agent have to destroy 
in order to be called a sterilizer?

Front 14

Escherichia coli and Enterobacter species.

Back 14

Which bacteria are considered the "index of fecal 
contamination"?

Front 15

Coliforms ferment lactose to produce acid and gas within 48 hours, while non‐coliforms do not
ferment lactose.

Back 15

What characteristic distinguishes coliforms from 
non‐coliforms?

Front 16

Lower temperatures have bacteriostatic effects on many microorganisms. Refrigeration can slow down, but not necessarily inhibit, microbial growth.

Back 16

How does refrigeration affect the microorganisms 
found in milk and food?

Front 17

Microorganisms that can grow under anaerobic conditions, such as Clostridium botulinum, can
grow and thrive under vacuum sealed conditions and release toxins that cause food poisoning.

Back 17

If improperly treated canned foods are vacuum 
sealed, what kind of bacteria might survive to  cause food poisoning?