Hemolysins are bacterial toxins that lyse red blood cells.
True
False
The Correct Answer is A
Hemolysins are bacterial exotoxins that specifically target and lyse red blood cells, releasing hemoglobin into the surrounding environment. They are produced by certain pathogenic bacteria, such as Streptococcus and Staphylococcus species, and contribute to nutrient acquisition by providing iron from hemoglobin. Hemolysins can cause varying degrees of red blood cell destruction, resulting in different patterns on blood agar: alpha hemolysis (partial lysis with greenish discoloration), beta hemolysis (complete lysis with clear zones), and gamma hemolysis (no lysis). Their activity is an important virulence factor in bacterial infections.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
A. A thick peptidoglycan layer: Gram-positive bacteria have a thick peptidoglycan layer, which retains the crystal violet-iodine complex during Gram staining. Gram-negative bacteria have a much thinner peptidoglycan layer, which does not retain the stain after decolorization.
B. No cell wall: Gram-negative bacteria do have a cell wall; it is just structurally different from Gram-positive bacteria. Their wall consists of a thin peptidoglycan layer sandwiched between the inner cytoplasmic membrane and an outer membrane containing lipopolysaccharides.
C. An outer membrane containing lipopolysaccharide (LPS): Gram-negative bacteria possess an outer membrane external to the peptidoglycan layer. This outer membrane contains LPS, which contributes to the structural integrity of the cell, acts as an endotoxin, and protects against certain antibiotics and host defenses. The presence of LPS is a key distinguishing feature.
D. Teichoic acids in their cell wall: Teichoic acids are found only in the cell walls of Gram-positive bacteria. They provide structural support, contribute to cell wall maintenance, and help with adherence, but are absent in Gram-negative bacteria.
Correct Answer is C
Explanation
A. Pink: Pink indicates Gram-negative bacteria, which do not retain the crystal violet stain during the decolorization step and are counterstained with safranin. Gram-positive bacteria are not pink after Gram staining.
B. Red: Red is another way to describe the color of Gram-negative bacteria after counterstaining with safranin. Gram-positive bacteria do not take up the red counterstain because they retain the primary crystal violet stain.
C. Purple: Gram-positive bacteria appear purple after Gram staining. Their thick peptidoglycan cell walls trap the crystal violet-iodine complex even after alcohol or acetone decolorization, allowing them to retain the purple color and be distinguished from Gram-negative bacteria.
D. Colorless: Colorless cells would indicate a failure to stain or a decayed sample. Gram-positive bacteria are never colorless after a proper Gram staining procedure.
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