HEK, MAC, EMB (week 5)

Which type of organisms can be differentiated from each other using the HEK media?

• Spore-forming gram-positive bacilli

• Non-spore-forming gram-negative bacilli

• Lactose-fermenting gram-positive cocci

• Non-lactose-fermenting gram-positive rods

What was the significant contribution of MacConkey agar?

• It inhibited all bacterial growth

• It allowed identification of pathogenic enteric bacteria by lack of lactose fermentation

• It enhanced the growth of gram-positive bacteria

• It was the first media to use antibiotics

Which genera did EMB media allow a visual distinction between?

• Bacillus and Clostridium

• Escherichia coli and Salmonella

• Staphylococcus and Streptococcus

• Lactobacillus and Bifidobacterium

What is the primary purpose of Hektoen enteric agar?

• To recover gastrointestinal pathogens like Salmonella and Shigella

• To enhance the growth of all bacteria

• To inhibit the growth of all pathogens

• To recover only nonpathogenic bacteria

How does Hektoen enteric agar differentiate between pathogenic and nonpathogenic coliforms?

• By color change due to acid production

• By size of the colonies

• By smell of the colonies

• By the speed of growth

What color do colonies appear on Hektoen enteric agar if they are able to ferment lactose, sucrose, or salicin?

• Greenish blue

• Bright red

• Salmon-pink to orange-yellow

• Dark purple

What is the role of bile salts in Hektoen enteric agar?

• To enhance the growth of all bacteria

• To inhibit most gram-positive organisms

• To provide nutrients for bacteria

• To change the color of the medium

Which organisms are unable to utilize lactose, sucrose, and salicin in Hektoen enteric agar?

• Nonpathogenic coliforms

• Pathogenic coliforms

• Salmonella and Shigella

• All gram-negative bacteria

What is the role of thiosulfate and ferric ammonium citrate in HE agar?

• To provide nutrients for bacterial growth

• To inhibit the growth of all bacteria

• To detect Salmonella by producing H₂S gas

• To enhance the color of bacterial colonies

What color does a nonpathogenic organism colony appear on HE agar?

• Black or with a black center

• Orange-yellow, sometimes with a black center

• Green with a blue center

• Red with a white center