Microbiology Lab Techniques: Media, Streaking, Hemolysis, and Antibiotic Testing

What is the streak method used for?

To separate and isolate bacteria colonies on a solid agar surface.

What are examples of primary media used in microbiology?

T-Soy Agar (TSA) and Blood Agar Plate (BAP).

What is the first step in the streak method?

Write your initials, date, and experiment number on the plate.

What is the order of colony numbers in streaking?

IV < III < II < I.

What does colony morphology refer to?

The characteristics of colonies such as shape, size, and pigmentation.

What is the purpose of Blood Agar?

To assess hemolytic activities and provide nutrients for fastidious organisms.

What are the three types of hemolysis observed on Blood Agar?

Alpha hemolysis, Beta hemolysis, and Gamma hemolysis.

What is the appearance of Alpha hemolysis on Blood Agar?

Colonies appear dark-greenish due to partial breakdown of red blood cells.

What is the appearance of Beta hemolysis on Blood Agar?

Colonies appear bright/clear and transparent due to complete breakdown of red blood cells.

What is the selective agent in Mannitol Salt Agar (MSA)?

High NaCl concentration (~7.5%-10% NaCl) that selects for gram-positive bacteria.

What happens when bacteria ferment mannitol in MSA?

The pH drops, causing the phenol red indicator to turn yellow.

What is the purpose of MacConkey Agar?

To isolate Gram-negative enteric bacteria and differentiate lactose fermenting from non-fermenting bacteria.

What is the selective agent in MacConkey Agar?

Crystal violet and bile salts that inhibit growth of gram-positive bacteria.

What does the neutral red indicator in MacConkey Agar indicate?

It turns red at a pH below 6.8, indicating lactose fermentation.

What are the two bacterial cultures tested for disinfectant effectiveness?

E. coli and B. subtilis.

What is the goal of the Kirby-Bauer antibiotic testing?

To examine antibiotic susceptibility of bacterial cultures.

What indicates the effectiveness of an antibiotic in the Kirby-Bauer test?

The size of the zone of inhibition around the antibiotic disk.

What is a characteristic of Staphylococcus species?

They are Gram-positive cocci and catalase positive.

What does a positive coagulase test indicate?

Solid clot formation, indicating the presence of coagulase enzyme.

What is the result of a positive catalase test?

Bubbles produced when hydrogen peroxide is broken down.

What does a Novobiocin sensitivity test measure?

The ability of bacteria to grow in the presence of Novobiocin.

What indicates a sensitive Novobiocin test?

Zone of inhibition greater than 16 mm.

What indicates a resistant Novobiocin test?

Zone of inhibition less than 12 mm.

What type of media is T-soy agar classified as?

General purpose media.

What is an enriched media example?

Blood Agar, which is supplemented with sheep blood.

What is the significance of the hemolytic properties on BAP?

To assess the breakdown of red blood cells by bacteria.

What is the effect of exposure time on disinfectant effectiveness?

Longer exposure times generally increase effectiveness against bacteria.

What are the two main types of bacterial growth inhibition by disinfectants?

Bactericidal (kills bacteria) and Bacteriostatic (stops growth).

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