Differential & Selective Media, Chemical Control, Antibiotics

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Microbiologists often used multiple types of media to cultivate microorganisms in order to

grow a particular organism or obtain information about the biochemical properties of the organisms that grow

Growth on MacConkey agar that is pinkish-red color indicates:

he organism has the ability to ferment lactose, and is probably a coliform.

What does Columbia CNA (C-CNA) Agar differentiate?

hemolytic patterns.

Function of dyes eosin and methylene blue:

inhibit gram-positive growth and select for gram-negative organisms

Function of crystal violet and bile salts on MacConkey Agar

inhibit most gram-positive organisms select for gram-negative organisms

What is the differential ingredient in Eosin Methylene Blue Agar (EMB)?

lactose

What is the differential ingredient in MacConkey Agar?

lactose

What does MacConkey Agar differentiate?

lactose fermentation

What does Eosin Methylene Blue Agar (EMB) differentiate?

lactose fermentation - strong vs. weak

What is the differential ingredient Mannitol Salt Agar (MSA)?

mannitol

What does Mannitol Salt Agar (MSA) differentiate?

mannitol fermentation

Additive effect of Antibiotics means

means that the overall effect of the antibiotic combination is no greater than the sum of the individual antibiotics

disk diffusion assay

method to test the effectiveness of antimicrobial chemicals

What is the pH indicator in MacConkey Agar?

neutral red

What is the pH indicator in Mannitol Salt Agar (MSA) plates?

phenol red

Function of colistin & nalidixic acid in Columbia CNA (C-CNA) Agar

prohibit the growth of most gram-negative Gram-positive organisms are allowed to grow.(Staphylococcus and Streptococcus)

Epsilometer or E test

quantitatively measures the minimal inhibitory concentration (MIC) of the antibiotic for the microorganism being tested

What type of media is Mannitol Salt Agar (MSA)?

selective and differential

How are selective properties of microbiological media different from differential properties of microbiological media?

selective media composed ingredients to inhibit the growth of certain microbes, while allowing others to grow differential media contains ingredients or chemicals that help to visually distinguish which species do or don't carry out a specific biochemical process.

Three commonly used types of media are

selective media, differential media enriched media.

Antimicrobial therapy is based on

selective toxicity

What does Mannitol Salt Agar (MSA) selects for?

selects for halotolerant bacteria

why is solid media is usually employed with selective and differential media?

so that individual colonies may be isolated.

Why are the C-CNA and blood plates incubated in the Anaeropak box?

so they can be incubated in an environment enriched with carbon dioxide.

Antibiotics are

substances produced as metabolic products of one microorganism which inhibit or kill other microorganisms;

Often, most differential media contain a___,___and__ indicator

substrate chemical indicator pH indicator

Define. Selective media

suppresses the growth of some microorganisms while allowing the growth of others (i.e., it selects for certain microbes)

Growth on mannitol salt agar indicates

that the organism is Halotolerant

Growth on Eosin Methylene Blue agar which exhibits a green metallic sheen indicates Example

the organism can ferment lactose to form strong acid end-products. (Q1) is not inhibited by eosin and methylene blue Escherichia coli

Growth on Eosin Methylene Blue agar, which is a pink color indicates Example

the organism can ferment lactose to form weak acid end-products (Q2 Maybe Q3) is not inhibited by eosin and methylene blue Enterobacter aerogenes

Growth on Eosin Methylene Blue agar indicates Example:

the organism can grow in the presence of the dyes eosin and methylene blue and is likely a gram-negative (Q4) is not inhibited by eosin and methylene blue Morganella Morganii

A change in the color of the Mannitol Salt Agar (MSA) from pink to yellow indicates:

the organism has the ability to ferment mannitol (red arrow)

Absence of growth on Eosin Methylene Blue agar indicates Example

the organism is Gram-positive is inhibited by eosin and methylene blue Streptococcus mutans

Growth on MacConkey agar indicates:

the organism is gram-negative Resistant to crystal violet and bile salts

Growth on Columbia CNA agar indicates

the organism is resistant to the antibiotics colistin and naladixic acid, and is likely a gram-positive.

Antimicrobial chemotherapy is

the use of chemicals to inhibit or kill microorganisms in or on the host

What does Blood agar differentiate?

Differentiation among Gram-positive cocci Bacteria with hemolysins

Which chemical would you choose if you wanted maximum effectiveness against both E. coli and S. aureus?

Clorox Most effective

If you wanted to select for Gram-positive bacteria, what type(s) of agar could you use?

Columbia CNA Agar

What type of media is Blood Agar?

Differential

Example of Gram-negative bacteria that ferment lactose

Enterobacter aerogenes (Q1) Escherichia coli (Q2)

Example of Gram-positive cocci bacteria Alpha hemolytic

Enterococcus Faecalis

Bacteria: Growth + alpha hemolysis on C-CNA plates

Enterococcus faecalis

Compare and contrast the Disk Diffusion and Epsilon tests for determining antibiotic susceptibility. Is one better than the other? Why or why not?

Epsilon test is better because the measurement is more accurate

What does this media select for Columbia CNA (C-CNA) Agar?

Gram- positive Resistan to colistin and nalidixin acid

What does it mean when bacteria wont grow on MacConkey agar?

Gram- positive (Q3) Streptococcus mutans is inhibited by bile salts and crystal violet

Beta hemolysis on blood plate results

Growth surrounded by a complete clearing of the blood indicates beta hemolysis. complete lysis of RBC and hemoglobin.

Alpha hemolysis on blood plate on blood plates results in

Growth surrounded by a partial clearing of the blood (often a greenish-grey color) partial lysis of RBC and hemoglobin.

Gamma hemolysis on blood plates results in

Growth which produces no changes in the blood indicates the bacteria are non-hemolytic.

What does Mannitol Salt Agar select for?

Halotolerant Bacteria

What does it mean when bacteria grow on MacConkey agar?

It is Gram-negative and not inhibited by bile salts and crystal violet

An unknown bacterium produces colorless colonies when inoculated onto an EMB plate. Predict what you would see if you inoculated that same unknown onto MacConkey agar, and why:

It will grow because the organism is gram-negative

Examples of selective media:

MSA - mannitol salt agar Mac - MacConkey agar EMB -eosin-methylene blue agar C-CNA- Columbia C-CNA agar.

Examples of differential media

MSA- mannitol salt agar, C-CNA blood agar Mac- MacConkey agar EMB- Eosin-methylene blue agar.

Which Selective media, selects for Gram-negative bacteria?

Mac - MacConkey agar Halotolerant EMB -eosin-methylene blue agar

If you wanted to select for Gram-negative bacteria only, what type(s) of agar could you use?

MacConkey Agar EMB

Example of Gram-negative bacteria that does not ferment lactose

Morganella Morganii (Q4) Salmonella typhimurium (Q4)

Example of Halotolerant organisms

SES Enterococcus faecalis (yellow) Staphylococcus xylosus (yellow) Staphylococcus epidermidis (pink)

What type of media is Columbia CNA (C-CNA) Agar?

Selective and differential

What type of media is Eosin Methylene Blue Agar (EMB)?

Selective and differential

What type of media is MacConkey Agar?

Selective and differential

Bacteria: Growth + Beta hemolysis on C-CNA plates

Staphylococcus xylosus

Example of Gram-positive cocci bacteria Beta hemolytic

Staphylococcus xylosus Streptococcus zooepidemicus

Example of Gram-positive cocci bacteria Gamma hemolytic

Streptococcus mutans

selective toxicity means

That the agent used must inhibit or kill the microorganism without seriously harming the host

Chemical agents work through two main mechanisms:

(1) Alteration of cell walls or cytoplasmic membranes (2) Interference with protein and nucleic acid structure.

2 general classes of antimicrobial chemotherapeutic agents:

(1) Antibiotics (2) Antimicrobial chemotherapeutic chemicals

synergistic effect of antibiotics means

(Arrow) the overall effect of the antibiotic combination is greater than the sum of the individual antibiotics. Antibiotics enhance the effect of each other.

The goal of antibiotic combination therapy is

(a) reduce the incidence of antibiotic-resistance (b) allow lower doses of antibiotics to be used (c) enhance the agents' antibacterial activity.

Describe how the disk diffusion assay works.

1. filter disks are impregnated with the chemical to be tested, and are placed on a plate inoculated w/ bacteria 2. plates are incubated 3. As a chemical diffuses into the agar, it becomes less concentrated

What the selective component Mannitol Salt Agar (MSA)?

7.5% sodium chloride

In order to be selectively toxic

Agent must interact with microbial function/structure that is either not present in the host, or is substantially different from that of the host.

Which organisms grow on the blood plates?

All organisms

The three types of hemolysis are:

Alpha hemolysis -partial/green Beta hemolysis - complete Gamma hemolysis-no hemolysis

Hemolysis patterns

Alpha- partial hemolysis Beta- complete hemolysis Gamma- no hemolysis

Disk Diffusion Assay or Kirby-Bauer test.

Antibiotic sensitivity testing to determine the susceptibility of bacteria to various antibiotics.

Define the term "zone of inhibition".

Area around the disk where the growth has been inhibited Organism is susceptible to a chemical

What is the differential ingredient Blood agar?

Blood

What is the differential ingredient in Columbia CNA (C-CNA) Agar?

Blood

How does Blood agar allows distinction among bacteria?

By the bacteria ability to lyse red blood cells hemolysins (exotoxins that lyses of RBC)

Which Selective media, selects for Gram-positive bacteria?

C-CNA- Columbia C-CNA agar. MSA - mannitol salt agar

An unknown bacterium produces colorless colonies when inoculated onto an EMB plate. Predict what you would see if you inoculated that same unknown onto C-CNA Agar agar, and why:

The organism will not reproduce because C-CNA does not allow gram-negative organisms to grow

What property or properties of gram-negative organisms would likely make them more resistant to crystal violet and bile salts than gram-positive organisms?

The outer membrane

size of this zone of inhibition depends on

The sensitivity of the bacteria to the specific chemical and the chemical's ability to diffuse through the agar.

Example of Halotolerant organisms that ferment mannitol

Yellow Enterococcus faecalis Staphylococcus xylosus

Organisms that are able to ferment the mannitol will produce ____ _____products which __ the pH. Causing the phenol red indicator to turn ____

acid fermentation lower yellow

Antibiotics used in combination can have 2 effects

additive effect synergistic effect

Define. Differential media

allows growth of more than 1 microorganism of interest but with morphologically distinguishable colonies based on specific biochemical properties of the organisms.

Which media, is only differential?

blood agar

Examples of enriched media

blood agar chocolate agar

Antimicrobial chemotherapeutic chemicals are

chemicals synthesized in the laboratory which can be used therapeutically on microorganisms.

What are the selective ingredients in Columbia CNA (C-CNA) Agar?

colistin & nalidixic acid

Define.Enriched media

contains specific growth factors needed by fastidious bacteria to support their growth.

What are the selective ingredients in MacConkey Agar?

crystal violet and bile salts

Mueller-Hinton agar is used to

determine additive and synergistic effects of drug combinations by placing the two antibiotic discs on a lawn of cells

What are the selective ingredients Eosin Methylene Blue Agar(EMB)?

eosin & methylene blue dyes

What does Eosin Methylene Blue Agar (EMB) select for?

gram-negative bacteria

What does MacConkey Agar select for?

gram-negative bacteria


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