Microbial Growth Media Overview

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Questions and Answers

Which medium is specifically designed to select for Staphylococcus aureus?

Mueller Hinton Agar

Mannitol salt Agar (correct)

Blood Agar Plate

Chocolate agar plate

What is the role of sodium deoxycholate in selective media?

It promotes the swarming of Proteus.

It differentiates yeast from bacteria.

It inhibits gram-positive organisms. (correct)

It selects for gram-negative organisms.

Which of the following is a characteristic of differential media?

It provides distinct colonial appearances to differentiate organisms. (correct)

It tests for the sensitivity of organisms to antibiotics.

It is primarily used for transporting organisms.

It inhibits the growth of all but selected organisms.

Which of the following is NOT a medium used for sensitivity testing?

Mannitol salt Agar Signup and view all the answers

What does the presence of phenol red in Russell’s Double sugar indicate?

Fermentation of lactose or dextrose. Signup and view all the answers

Which medium is used to test the motility of an organism?

Sulfide-Indole-Motility (SIM) Signup and view all the answers

What is the primary action of nystatin in certain media?

Inhibit the growth of yeasts. Signup and view all the answers

What type of medium is chocolate agar plate (CAP)?

It contains lysed red blood cells for growth enhancement. Signup and view all the answers

Which agar is used for differentiating lactose fermenters and non-lactose fermenters, and is considered the primary selective agar?

Mackonkey Agar Signup and view all the answers

What is the color indication of a mannitol fermenter on Mannitol Salt Agar?

Yellow Signup and view all the answers

What pH indicator is used in Gram Xylose Lysine Desoxycholate (XLD) Agar?

Phenol Red Signup and view all the answers

Which broth is specifically used to enhance the growth of Salmonella and Shigella?

Tetrathionate Broth Signup and view all the answers

What is the color for pathogenic organisms that appear on Hektoen Enteric Agar?

Blue Green Signup and view all the answers

Which agar is selectively for Staphylococcus species?

Mannitol Salt Agar Signup and view all the answers

What color do non-mannitol fermenters appear on Mannitol Salt Agar?

Pink Signup and view all the answers

Which of the following acts as a reducing agent to create an anaerobic environment deeper in the tube?

Thioglycolic Acid Signup and view all the answers

Which method is used to differentiate Mycobacterium leprae from M.tuberculosis?

Baumgarten’s Method Signup and view all the answers

What is the primary purpose of India Ink in microbiological staining?

To appear as a thick gelatinous capsule Signup and view all the answers

What type of bacteria are described as 'gram ghost' due to their difficulty in staining?

Mycobacterium Signup and view all the answers

Which technique is most useful for staining Legionella and Spirochetes?

Silver Impregnation Techniques Signup and view all the answers

Which special stains are primarily used for demonstration of specific microorganisms?

Antibody-conjugated Stains Signup and view all the answers

Which method involves overlapping the streak for testing susceptibility?

Overlap Streak Method Signup and view all the answers

What describes a method that starts streaking on one side and then turns halfway?

Interrupted Streak Method Signup and view all the answers

Which hemolytic pattern is characterized by a complete hemolysis with clear zones around colonies?

Beta hemolytic pattern Signup and view all the answers

Which method uses a calibrated loop to place inoculum for quantification of bacterial cultures?

Streaking for quantification Signup and view all the answers

What is the appearance of an organism described as having an umbrella-shaped pattern in semi-solid media?

Listeria monocytogenes Signup and view all the answers

Which term describes colonies that do not allow light to pass through?

Opaque Signup and view all the answers

What type of hemolytic pattern is characterized by greenish zones around colonies?

Alpha hemolytic pattern Signup and view all the answers

What does the Multiple Interrupted Streak Method refer to?

An advanced method of streaking with interruptions Signup and view all the answers

What is the primary stain used in the Ziehl-Neelsen Stain?

Carbol Fuchsin Signup and view all the answers

Which method uses a concave slide to demonstrate motility?

Hanging Drop Method Signup and view all the answers

Which component enhances the affinity of the primary stain in Gram staining?

Mordant Signup and view all the answers

What type of organism does the Acid-fast stain target?

Bacteria with mycolic acid in their cell walls Signup and view all the answers

What is indicated by a blue background in Ziehl-Neelsen Stain?

AFB (+) Red Bacilli Signup and view all the answers

What does False Gram Negative indicate?

Over decolorization Signup and view all the answers

Which stain uses a mixture of Auromine O and Rhodamine B dyes?

Fluorochrome Stain Signup and view all the answers

What counterstain is used in Fluorochrome Stain?

Potassium Permanganate Signup and view all the answers

Study Notes

Selective Media

Contains inhibitory agents that inhibit the growth of all organisms except those "selected" by specific growth conditions.

Differential Media

Provides distinct colonial appearances that differentiate between various groups of microorganisms.

Media for Sensitivity Testing

Mueller Hinton Agar (MHA) is the primary medium used for antibiotic susceptibility testing.

Transport Media

Used to preserve and prevent the drying and disintegration of microorganisms during transport.
Charcoal is often included in transport media.

Antibiotic Media

Contain specific antibiotics to select for organisms resistant to those antibiotics.
Vancomycin inhibits gram-positive bacteria.
Colistin inhibits gram-negative rods.
Nystatin, Anisomycin, and Amphotericin B inhibit yeast growth.

Media for Biochemical Reactions

Used to test biochemical activities and detect chemicals produced by microorganisms.

Russell's Double Sugar

Contains 1% lactose, 0.1% dextrose, nutrient agar, and phenol red as a pH indicator.

Kligler Iron Agar (KIA)

Same composition as Russell's Double Sugar, with the addition of agents to detect hydrogen sulfide production.

Triple Sugar Iron (TSI)

Same composition as KIA, with the addition of 1% sucrose.

Sulfide-Indole-Motility (SIM)

Semi-solid medium used to detect hydrogen sulfide production, motility, and serves as a biochemical medium for indole test.

Blood Agar Plate (BAP)

Supports the growth of non-fastidious bacteria and demonstrates hemolytic reactions.
5-10% defibrinated blood is used.
Citrate inhibits the growth of beta-hemolytic streptococci.

Chocolate Agar Plate (CAP)

Contains trypticase soy agar plus blood that has been chemically-treated or heat-treated (80°C) to lyse red blood cells.

Phenylethyl Alcohol Agar (PEA)

Sheep blood agar supplemented with Phenylethyl alcohol to inhibit the growth of gram-negative bacteria.

Columbia Agar Base

A nutritionally rich formula containing three peptone sources and 5% defibrinated sheep blood.

Eosin Methylene Blue Agar (EMB)

Differentiates lactose fermenters from non-lactose fermenters, based on colony color.

MacConkey Agar

Also differentiates lactose fermenters and non-lactose fermenters.
Frequently used as a primary selective and differential agar.

Mannitol Salt Agar

Selective for Staphylococcus sp.
Mannitol fermenters produce yellow colonies; non-fermenters produce pink colonies.

Hektoen Enteric Agar (HE)

Selectively slows the growth of most non-pathogenic gram-negative bacilli found in the gastrointestinal tract.
Non-enteric pathogens form orange to salmon-colored colonies.
Pathogenic organisms appear as blue-green colored colonies.

Xylose Lysine Desoxycholate (XLD) Agar

Contains Phenol red as a pH indicator.

Thiosulfate Citrate Bile Salt Sucrose Sugar (TCBS)

Peptone base agar with yeast extract and sucrose, used to detect fermentation.
Contains Bromothymol Blue as a pH indicator.

Tetrathionate Broth

Enhances the growth of Salmonella and Shigella, containing bile salts and sodium thionate.

Selenite Broth (Sel-F)

Enhances the growth of Salmonella and Shigella, containing sodium hydrogen selenite, which is toxic to most Enterobacteriaceae.

Alkaline Peptone Water (APW)

Used to enhance the growth of Vibrio.

Brain Heart Infusion

A naturally rich medium used to grow various organisms, often used to culture patient blood for bacteria.

Thioglycollate Broth

An enrichment broth most frequently used in diagnostic bacteriology.
Contains thioglycolic acid, which acts as a reducing agent, creating an anaerobic environment deeper in the tube, allowing anaerobic bacteria to grow.

Methods of Inoculation

Liquid Culture Media: Inoculated by shaking.
Butt Medium: Inoculated by stabbing.
Slant Medium: Streaked from bottom with a zigzag fashion.
Butt/Slant Medium: Stab the butt portion and streak with a zigzag fashion on the slant.
Plated Medium: Streaked.

Streak Plate Techniques

Radial Streak Method: Inoculum is placed on one side of the plate and brought to the other side in a concentric fashion.
Overlap Streak Method: Overlapping streaks are used, often for susceptibility testing.
Multiple Streak Method: The medium is divided into several divisions, and each division is streaked separately.
Interrupted Streak Method: The streaking starts on one side of the plate, stops halfway, the plate is turned 180 degrees, and the streaking continues.
Multiple Interrupted Streak Method: The most preferred method.
Streaking for Quantification: 1 µL (1:1000) or 10 µL (1:100) are used for urine cultures, the inoculated plate is cross-streaked with an ordinary inoculating loop.

Streak Plate Technique

Used for isolating pure cultures of organisms from mixed populations.

Colony Characteristics

Form/Shape/Margin: Describes the shape of colonies and their edges (smooth, filamentous, rough, irregular, mucoid).
Elevation: Determined by tilting the medium and looking at the side of the colony (flat, raised, convex).
Transparency:
- Transparent: Allows light to pass through completely.
- Translucent: Allows some light to pass through.
- Opaque: Does not allow light to pass through.
Hemolysis:
- Alpha hemolytic: Incomplete hemolysis, characterized by greenish zones around colonies.
- Beta hemolytic: Complete hemolysis, characterized by clear zones around colonies.
- Gamma hemolytic: Non-hemolytic, no zone around colonies.
- Double zone of hemolysis: Found in Clostridium perfringens, with a beta-hemolytic inner zone.
Pigment: Inherent characteristic of an organism, often expressed as colony color.

Growth in Broth and Semi-Solid Media

Listeria monocytogenes: Umbrella-shaped pattern in semi-solid media.
Certain Streptococcal species in thioglycolate: Vine or streamer effect and puffed balls.
Erysipelothrix rhusiopathiae: Test tube brush growth on semi-solid media.

Microscopic Techniques

Wet Mount Method: Inoculum or specimen is mixed with normal saline solution (NSS) to demonstrate the bacterial cell shape and arrangement.
Hanging Drop Method: Uses a concave slide to demonstrate motility.
Swarming Phenomenon: Motile organisms spread from the original site of inoculation on BAP and CAP, creating a thin film of growth.

Gram Staining

Primary Stain: Crystal violet.
Mordant: Gram's Iodine (enhances affinity of primary stain, forming CV-I complex).
Decolorizer: Acetone-Alcohol or 95% Ethyl Alcohol (lipid solvent and dehydrating agent).
Counterstain: Safranin (stains gram-negative bacteria).
False Gram-Negative: Loss of cell wall integrity caused by factors like antibiotic treatment, autolysis, aging, media, or temperature incubation, or over-decolorization.
False Gram-Positive: Incomplete decolorization or thick smear.

Acid-Fast Staining

Used for bacteria with mycolic acid in their cell walls.
Mycolic acid renders the cell resistant to decolorization, even with acid alcohol decolorizers.
Primary Stain (Ziehl-Neelsen): Carbol fuchsin.
Background (Ziehl-Neelsen): Blue.
Primary Stain (Kinyoun): Mixture of auramine O and rhodamine B dyes.
Background (Kinyoun): Green.
Counterstain (Fluorochrome): Potassium permanganate.
Background (Fluorochrome): Black.
Modified Acid-Fast Stain: Detects Nocardia, Legionella micdadei, and oocysts of Cyclospora, Cryptosporidium, and Isospora.

Special Stains

Lactophenol cotton blue: Used to stain fungi.
Fontana-Tribandeau: Used to stain spirochetes.

Key Exceptions

Gram-Positive Cocci: All except Neisseria, Branhamella (Moraxella), and Veillonella.
Lack of Cell Wall: Mycoplasma and Ureaplasma.
Difficult to Gram Stain: Legionella and Spirochetes (silver impregnation techniques are more useful).

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Description

This quiz covers various types of microbial growth media, including selective, differential, and antibiotic media. It aims to test your understanding of the properties and applications of these media in microbiology. Additionally, it explores media used for biochemical reactions and sensitivity testing.