Gram-Positive Bacteria

Question 1

What is the gram staining process?

Answer 1

Gram staining:
1. Crystal violet
2. Iodine fixes the crystal violet to the peptidoglycan
3. Decolorizer like acetone, rinses off any unbound crystal violet and disintegrates the lipids of the cell membranes
4. Safranin red counterstain turns the gram-negative bacteria reddish pink

Question 2

_ bacteria turn purple during staining due to their thick, mesh-like peptidoglycan cell wall

Answer 2

Gram-positive bacteria turn purple during staining due to their thick, mesh-like peptidoglycan cell wall
* The cell wall is cross linked which allows it to pick up the crystal violet stain and resist rinsing by acetone

Question 3

Because gram-positive bacteria have no _ , the cross-linking in their _ is the last line of defense against osmotic stress

Answer 3

Because gram-positive bacteria have no outer membrane , the cross-linking in their cell wall is the last line of defense against osmotic stress

Question 4

Beta-lactam antibiotics target gram-positive bacteria by binding to _ which inhibits peptidoglycan cross-linking and decreases cell wall stability

Answer 4

Beta-lactam antibiotics target gram-positive bacteria by binding to penicillin-binding proteins (PBPs) which inhibits peptidoglycan cross-linking and decreases cell wall stability
* Bacteria die from osmolysis

Question 5

The peptidoglycan cell wall is covalently linked to _ , a long anionic polymer made of glycerol and phosphate repeats

Answer 5

The peptidoglycan cell wall is covalently linked to teichoic acid , a long anionic polymer made of glycerol and phosphate repeats
* Also lipoteichoic acids are the same thing but are linked to the head groups of membrane lipids

Question 6

Teichoic acid and lipoteichoic acids give the bacterial cell a _ charge

Answer 6

Teichoic acid and lipoteichoic acids give the bacterial cell a negative charge

Question 7

Only _ bacteria can make spores

Answer 7

Only gram-positive bacteria can make spores

Question 8

Capsules can help the bacteria to resist _ and _

Answer 8

Capsules can help the bacteria to resist opsonization and phagocytosis

Question 9

_ are the structures at the tops of the pili which form bonds with cell surface molecules

Answer 9

Fimbriae are the structures at the tops of the pili which form bonds with cell surface molecules

Question 10

_ are a polysaccharide coating made of glycocalyx that is secreted by some gram-positive bacteria

Answer 10

Biofilms are a polysaccharide coating made of glycocalyx that is secreted by some gram-positive bacteria
* Mediates adherence to a surface
* Protection from antibiotics and immune response

Question 11

_ are polypeptides that get secreted from gram-positive or gram-negative bacteria and harm the host by altering the host’s cell structure or function

Answer 11

Exotoxins are polypeptides that get secreted from gram-positive or gram-negative bacteria and harm the host by altering the host’s cell structure or function

Question 12

_ are components of gram-negative bacterial outer membrane or cell walls

Answer 12

Endotoxins are components of gram-negative bacterial outer membrane or cell walls

Question 13

_ is the capability of some gram-positive bacteria to invade host cells and live inside the phagosome or escape the phagosome; they replicate intracellularly and escape immune surveillance

Answer 13

Intracellular invasion is the capability of some gram-positive bacteria to invade host cells and live inside the phagosome or escape the phagosome; they replicate intracellularly and escape immune surveillance

Question 14

_ converts fibrinogen to an insoluble fibrin capsule that then surrounds microorganisms and limits immune cell access to them

Answer 14

Coagulase converts fibrinogen to an insoluble fibrin capsule that then surrounds microorganisms and limits immune cell access to them

Question 15

_ are lipids and proteins that can lyse RBCs by destroying their cell membrane

Answer 15

Hemolysins are lipids and proteins that can lyse RBCs by destroying their cell membrane

Question 16

_ are enzymes that facilitate spread throughout the host’s tissues and include hyaluronidase, DNase, collagenase, lipase, elastase, and streptokinase

Answer 16

Spreading factors are enzymes that facilitate spread throughout the host’s tissues and include hyaluronidase, DNase, collagenase, lipase, elastase, and streptokinase

Question 17

_ are powerful exotoxins that initiate the stimulation of the immune response by tightly binding the MHC class II molecules to T-cell receptors on antigen-presenting cells

Answer 17

Superantigens are powerful exotoxins that initiate the stimulation of the immune response by tightly binding the MHC class II molecules to T-cell receptors on antigen-presenting cells
* They can induce antigen-independent T cell activation and proinflammatory cytokines
* This is referred to as a cytokine storm

Question 18

The two most likely modes of antibiotic resistance are _ and _

Answer 18

The two most likely modes of antibiotic resistance are conjugation and transduction
* Spontaneous mutation is rare

transduction shown

Question 19

_ enzyme gives some gram-positive bacteria the ability to inactivate penicillin and its derivatives

Answer 19

Beta-lactamase enzyme gives some gram-positive bacteria the ability to inactivate penicillin and its derivatives
* Beta-lactamase cleaves the beta-lactam ring of beta-lactam antibiotics

Question 20

Streptococcus pneumoniae also has resistance to beta-lactam because it has unique _ encoded in the genome sequence

Answer 20

Streptococcus pneumoniae also has resistance to beta-lactam because it has unique mutated penicillin-binding proteins encoded in the genome sequence
* This decreases the drug’s affinity for the bacteria

Question 21

_ accounts for about 40% of all nosocomial (hospital-acquired) Staph aureus infections in the US

Answer 21

MRSA accounts for about 40% of all nosocomial (hospital-acquired) Staph aureus infections in the US
* Vancomycin had been a common drug to treat antibiotic-resistant strains like this but now resistant strains are increasing

Question 22

_ produces yellow pigment on trypticase soy agar

Answer 22

Staph aureus produces yellow pigment on trypticase soy agar

Question 23

The _ test can differentiate gram-positive cocci by their ability to catabolize hydrogen peroxide into wtaer and oxygen

Answer 23

The catalase test can differentiate gram-positive cocci by their ability to catabolize hydrogen peroxide into wtaer and oxygen
* This is important to differentiate between staphylococcus (+) from streptococcus (-)

Question 24

Coagulase is a unique enzyme to _ and a positive test indicates that the bacteria can produce coagulase, which creates an insoluble fibrin capsule around the microorganism

Answer 24

Coagulase is a unique enzyme to S aureus and a positive test indicates that the bacteria can produce coagulase, which creates an insoluble fibrin capsule around the microorganism

Question 25

The _ reaction can demonstrate whether bacteria possess a capsule

Answer 25

The Quellung reaction can demonstrate whether bacteria possess a capsule
* Also called the Neufeld-Quellung test
* In a positive reaction, the antibodies bind to the capsule, making it look enlarged and opaque in microscopy

Capsules can also be detected with latex bead agglutination and staining with India Ink

Question 26

The three types of hemolysis (RBC breakdown) are _ , _ , and _

Answer 26

The three types of hemolysis (RBC breakdown) are alpha , beta , and gamma

Question 27

_ hemolysis (partial breakdown) shows a green darkening of the blood agar

Answer 27

alpha hemolysis (partial breakdown) shows a green darkening of the blood agar –> color from hydrogen peroxide oxidizing hemoglobin

Question 28

_ hemolysis results in a complete clearing of blood agar

Answer 28

beta hemolysis results in a complete clearing of blood agar

Question 29

_ hemolysis is designated for when no hemolysis occurs and there is no change in the blood agar

Answer 29

gamma hemolysis is designated for when no hemolysis occurs and there is no change in the blood agar