A 67-year-old patient with chronic alcoholism presents with severe pneumonia. Blood cultures grow bacteria that evade phagocytosis and demonstrate increased virulence due to an external protective layer surrounding the cell wall. Which bacterial structure is primarily responsible for this immune evasion?
Flagella
Capsule
Fimbriae
Lipopolysaccharide
Peptidoglycan
The Correct Answer is B
A. Flagella: Flagella are whip-like appendages that provide motility to bacteria, allowing them to move toward nutrients or away from harmful environments. While motility can contribute to colonization, flagella do not provide a protective barrier against phagocytosis or immune system attack.
B. Capsule: The capsule is an external polysaccharide or protein layer that surrounds the bacterial cell wall. It prevents recognition and ingestion by phagocytes, inhibits complement activation, and contributes to increased virulence. Encapsulated bacteria, such as Streptococcus pneumoniae, are particularly problematic in patients with weakened immune systems, like those with chronic alcoholism, because the capsule impedes effective immune clearance.
C. Fimbriae: Fimbriae are short, hair-like projections on the bacterial surface that facilitate attachment to host cells and surfaces. They play a role in colonization and biofilm formation but do not directly prevent phagocytosis or enhance survival against immune defenses.
D. Lipopolysaccharide: Lipopolysaccharide (LPS) is a component of the outer membrane of Gram-negative bacteria that contributes to endotoxin activity, triggering inflammation and septic shock. While LPS can affect host immune responses, it does not provide a direct physical barrier to phagocytosis.
E. Peptidoglycan: Peptidoglycan forms the rigid structural layer of the bacterial cell wall, providing shape and protection against osmotic pressure. Although essential for bacterial integrity, peptidoglycan does not prevent immune recognition or phagocytosis in the way that a capsule does.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
Bacteria with a thin peptidoglycan layer and an outer membrane containing lipopolysaccharide (LPS) are characteristic of gram-negative organisms. During Gram staining, the thin peptidoglycan layer cannot retain the crystal violet-iodine complex, so the cells take up the counterstain (safranin) and appear pink under a microscope. Common gram-negative bacilli causing urinary tract infections include Escherichia coli, which often presents with dysuria, fever, and bacilli observed on urine microscopy. Gram-positive bacteria have a thick peptidoglycan layer and lack an outer membrane. This structure allows them to retain the crystal violet stain and appear purple.
Correct Answer is E
Explanation
A. Cilia: Cilia are short, hair-like projections that cover the surface of some protozoa. They beat in coordinated waves to facilitate locomotion and help direct food particles toward the oral groove. Ciliary movement allows protozoa such as Parameciumto navigate aquatic environments efficiently.
B. Flagella: Flagella are long, whip-like appendages that provide motility to certain protozoa, including Euglena. The undulating motion of flagella propels the organism through liquid environments, enabling it to seek nutrients and favorable conditions.
C. Pseudopods: Pseudopods are temporary cytoplasmic extensions formed by the flow of cytoplasm. Protozoa such as Amoebause pseudopods for movement and phagocytosis, allowing them to engulf food particles and migrate toward stimuli.
D. Cilia and pseudopods only: While some protozoa possess cilia and pseudopods, this option excludes flagella, which are a common motility structure in many protozoan species. Limiting motility to only these two structures does not represent the full range observed in protozoa.
E. Cilia, flagella, and pseudopods: Protozoan motility encompasses all three structures. Different species utilize one or more of these mechanisms depending on their morphology and ecological niche. Cilia, flagella, and pseudopods collectively allow protozoa to move, capture food, and respond to environmental stimuli.
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