Selective and Differential Media

These flashcards cover key terms and concepts related to selective and differential media in microbiology, focusing on their applications, compositions, and the significance of various indicator organisms.

Mannitol Salt Agar (MSA)

A medium that selects for salt-tolerant bacteria and differentiates based on mannitol fermentation.

Selective Media

Media that contain chemicals to inhibit the growth of unwanted bacterial species while allowing the desired species to grow.

Differential Media

Media used to identify bacterial species based on differences in metabolic activities.

Gram + Halophilic Species

Bacteria that can tolerate high salt concentrations; example includes Staphylococcus.

Phenol Red

A pH indicator used in MSA to determine acidity based on mannitol fermentation.

Lactose Fermentation

The metabolic process by which certain bacteria convert lactose into acid, lowering the pH.

Enterobacteriaceae

A family of Gram-negative bacteria that are commonly found in the intestinal tract.

Coliforms

Bacteria that ferment lactose, used as indicators of fecal contamination in water.

Eosin Methylene Blue Agar (EMB)

A medium that selects against Gram-positive bacteria and differentiates based on lactose fermentation.

Bile Salts

Compounds produced by the liver to inhibit Gram-positive bacteria and allow growth of Gram-negative enterics.

MacConkey Agar (MAC)

A selective and differential agar used to isolate Gram-negative bacteria and differentiate lactose fermenters.

Esculinase

An enzyme that breaks down esculin into glucose and esculetin, used in Bile Esculin Agar.

Acidic pH

A pH lower than 6.8, indicating the presence of acid end products from fermentation.

Electrolytes during fermentation

Substances such as acetate or phosphate that can influence the fermentation process.

Salmonella enterica

A species of bacteria known for causing typhoid fever and gastroenteritis.

Staphylococcus aureus

A pathogenic species of staphylococcus that ferments mannitol, indicated by yellow growth on MSA.

Gram-negative bacteria

Bacteria that do not retain the crystal violet stain used in the Gram-staining procedure.

Bile Esculin Agar (BEA)

A medium that selects for enterococci and Group D streptococci based on the breakdown of esculin.

Dark Brown/Black Precipitate

Indicates positive reaction in Bile Esculin Agar, forming due to the reaction of esculetin with ferric citrate.

Lactose Indicators

Neutral red or phenol red, used in MAC and EMB to indicate lactose fermentation.

Fermentation product

Substance produced by bacteria during the fermentation process, often leading to pH changes.

Critical pH Levels

pH < 6.8 indicates acid, pH 6.8-7.4 neutral, and pH > 7.4 indicates alkalinity.

Escherichia coli

A common bacterium in the human intestine that can be pathogenic under certain conditions.

Facultative Anaerobes

Bacteria that can grow in both the presence and absence of oxygen.

Group D Streptococci

A subgroup of streptococci categorized based on their ability to hydrolyze esculin.

Anthraquinone

A type of synthetic dye; in this context, refers to the dyes used in EMB.

Streptococcus bovis

A species of Group D streptococci that can be identified using Bile Esculin Agar.

Bacterial Metabolism

The chemical processes within bacteria that convert nutrients into energy and byproducts.

pH Scale

A scale ranging from 0 to 14 used to specify the acidity or alkalinity of a solution.

Electrophoresis in microbiology

A method to separate bacteria based on their size and charge during analysis.

Enteric Bacteria

Bacteria that reside in the intestinal tract and can cause gastrointestinal diseases.

Nutrient Agar

A general-purpose medium that supports a wide variety of microbial growth.

Fecal Coliforms

Bacteria found in the intestinal tract of warm-blooded animals, used as a water contamination indicator.

Antibiotic Selection

The use of antibiotics in selective media to inhibit the growth of specific bacteria.

Selective Pressure

Environmental factors that favor certain types of bacteria over others, influencing growth.

Ethanol and organic acids

Products of fermentation that can inhibit growth of some bacterial species.

Color Change in Agar

A visual indication of metabolic activity, seen as a result of pH changes during fermentation.