quiz 2 practice test

Mannitol Salt Agar (MSA) color change

A change from pink to yellow indicates the bacterium has metabolized mannitol, producing acid and lowering the pH below 6.8.

Non-mannitol metabolizing bacteria on MSA

They grow but do not cause color change; the medium remains pink.

Objective of EMV medium

To assess whether bacteria can metabolize lactose.

Green metallic sheen on EMV

Indicates effective lactose metabolism, particularly with E. coli.

Appearance of green sheen over time

It may fade to dark purple growth but still signifies strong lactose metabolism.

Characteristics of Spirit Blue Medium

Non-selective but differential; supports both Gram positive and Gram negative bacteria and tests for lipase enzyme presence.

Clearing around bacterial growth in Spirit Blue Medium

Indicates the presence of lipase, which breaks down lipids.

Function of glucose in TSI Medium

Serves as a limited carbon source for testing lactose and sucrose metabolism when glucose is exhausted.

Color change in TSI Medium upon fermentation

Turns yellow due to acidic byproducts from sugar metabolism.

Red color in TSI Medium

Indicates that only peptone is metabolized, resulting in basic conditions due to ammonia.

Effect of peptone on TSI Medium pH

Presents a rise in pH, turning the medium red.

Role of Sodium Thiosulfate in TSI Medium

Releases elemental sulfur in acidic conditions, which can be reduced to hydrogen sulfide by bacteria.

Indication of hydrogen sulfide production in TSI Medium

Black precipitate forms when ferric ammonium citrate binds with hydrogen sulfide.

Pathways for carbon metabolism

Glycolysis for sugar breakdown and Krebs cycle for decarboxylation.

Stab and streak method for TSI

Creates aerobic and anaerobic environments for bacterial growth observation.

Successful esculin hydrolysis in Bile Esculin Test

Indicated by a dark brown/black coloration from the metabolization of esculin.

Positive results in MIO test for indole production

A red ring appears after adding Kovac's reagent, indicating tryptophanase presence.

Presence of putrescine in MIO test

Signifies ornithine decarboxylation, raising pH and changing the medium from yellow to purple.

Precautions when handling Pseudomonas

Always change gloves due to its increased virulence.

Medical significance of hemolysis on Blood Agar Plates

Degree of hemolysis correlates with pathogenicity, for example, beta-hemolytic strep can cause serious infections.

Snyder Test Agar indication for lactobacilli

Detects them by color change from green to yellow due to lactic acid production.

Anaerobic chamber environment for bacteria

Removes oxygen and introduces nitrogen or carbon dioxide for anaerobic growth.

Gas production in TSI Medium

Indicated by cracks or bubbles in the medium.

Crucial lab safety measure with virulent bacteria

Importance of proper inoculation techniques to avoid contamination.

Presence of ferric citrate in Bile Esculin Test

Crucial for detecting esculetin reaction product which forms coloration.

Snyder Test target bacteria

Agar is designed to detect lactobacilli, which relate to dental caries risk.

Triglyceride breakdown in Spirit Blue Medium

Diminished blue color indicates lipase activity.

Importance of uninhibited surface in Spirit Blue Medium inoculation

To clearly observe the halo effect around bacterial growth.

Beta-hemolysis appearance on Blood Agar Plates

Clear zones surrounding growth indicate complete breakdown of red blood cells.

Importance of fermentation tests like TSI and Bile Esculin

Discern metabolic capabilities of bacteria, aiding in identification.