Microbiology Lab Exercises 9-12 Review

Vocabulary-style flashcards covering microbial characteristics, artificial culture media, and biochemical diagnostic tests.

Staphylococcus epidermidis

Gram positive, cocci in clusters, catalase positive, coagulase negative, non-motile, and rarely pathogenic.

Staphylococcus aureus

Gram positive, cocci in clusters, catalase positive, coagulase positive, non-motile, and the most important pathogen in the genus Staphylococcus.

Nutrient Media

Artificial culture media containing ingredients like water, salt, agar, and amino acids designed to satisfy growth requirements for most bacteria; examples include Tryptic Soy Agar (TSA) and Tryptic Soy Broth (TSB).

Selective Media

Media that encourages the growth of a desired microbe while inhibiting most others using dyes, antibiotics, or chemicals; examples include Columbia Nalidixic Acid Agar (CAN) and Mannitol Salt Agar (MSA).

Differential Media

Media used to distinguish a desired bacterium from closely related species in a specimen; examples include Blood Agar Plate (BAP), MacConkney Agar (MAC), and Salmonella Shigella Agar (SSA).

MacConkney Agar (MAC)

A medium that inhibits gram-positive bacteria and promotes gram-negative growth; it differentiates lactose-fermenting bacteria (like E. coli) from non-lactose-fermenting bacteria (like Salmonella).

Mannitol Salt Agar (MSA)

A medium using $7.5\%$ sodium chloride as a selective agent and mannitol as a differential property; used to isolate and differentiate Staphylococcus species.

Facultative halophiles

Organisms, such as those in the genus Staphylococci, that are able to grow in high-salt environments.

Alpha-hemolytic colonies

Colonies on a Blood Agar Plate that cause partial breakdown of red blood cells, resulting in a greenish-brown zone.

Beta-hemolytic colonies

Colonies on a Blood Agar Plate that cause complete breakdown of red blood cells, resulting in a clear zone.

Gamma-hemolytic colonies

Colonies on a Blood Agar Plate that cause no breakdown of red blood cells and produce no visible zone.

DNase Agar

A medium containing DNA and methyl green indicator used to identify bacteria that produce the enzyme DNase; a positive result turns the agar clear.

Coagulase Test

A test using rabbit plasma to identify bacteria that produce the enzyme coagulase, which causes blood plasma to clot or clump.

Catalase Test

A test that identifies the presence of the enzyme catalase, which breaks down toxic $H_2O_2$ into water and oxygen; used to differentiate Staph from Strep.

Enterococcus faecalis

Gram-positive, cocci in chains, catalase negative, coagulase negative, and nonmotile bacteria that is positive for bile esculin hydrolysis.

Streptococcus pyogenes

Gram-positive, cocci in chains, catalase negative, coagulase negative, nonmotile bacteria belonging to Group A beta-hemolytic streptococci.

Bacitracin Test

A test used to detect Group A beta-hemolytic strep (like S. pyogenes); sensitive bacteria will show a zone of inhibition around the bacitracin disk.

Bile Esculin

A selective and differential medium where sodium azide inhibits gram-negative bacteria, and Enterococci are identified by their ability to hydrolyze esculin in the presence of bile, turning the medium dark brown or black.

Enterobacteriaceae

A family of gram-negative, rod-shaped, non-endospore forming bacteria that includes E. coli, Salmonella, and Shigella.

Coliforms

Lactose-fermenting members of the Enterobacteriaceae family that generally only cause disease outside the GI tract; examples include E. coli and Enterobacter aerogenes.

IMViC series

A group of four tests used for bacterial identification: Indole, Methyl red, Voges-Proskauer, and Citrate.

Eosin Methylene Blue Agar (EMB)

A selective and differential medium that uses methylene blue and bile salts to inhibit gram-positive bacteria and lactose to differentiate between fermenters and non-fermenters.

Indole Test

A test using Ehrlich’s Reagent to determine if bacteria can break down the amino acid tryptophan to produce indole; a positive result is a red ring.

Methyl Red Test

A test used to determine if bacteria can break down glucose into acidic end products; a positive result is a red broth color.

Voges-Proskauer (VP) Test

A test using O’Meara’s reagent to determine if bacteria can break down glucose into acetoin; Enterobacter aerogenes is positive (red band).

Citrate Test

A test to determine if bacteria can use citrate as their only source of carbon; a positive result changes the medium from green to blue.

Urease Test

Determines if bacteria can break down urea into ammonia and carbon dioxide; Proteus vulgaris is a positive example.

Phenylalanine Deaminase (PAD) Test

Determines if bacteria can break down phenylalanine into phenylpyruvic acid; Proteus vulgaris is positive and Serratia marcescens is negative.

Triple Sugar Iron (TSI)

An agar containing glucose, lactose, and sucrose used to detect sugar fermentation (A for acid/yellow, K for alkaline/red), gas production, and hydrogen sulfide ($H_2S$) production.

SIM Media

A medium used to detect sulfide ($H_2S$) production (blackening), indole production (red ring), and motility (cloudy or hazy appearance).