Lange Microbiology Self-Assessment


Abdominal Cramping & Nausea

CASE Report:

A 73-year-old woman is admitted to the hospital for intravenous treatment of an abscess caused by Staphylococcus aureus. Subsequent to her treatment and discharge from the hospital, it is necessary to disinfect the hospital room. One thousand of the S aureus cells are exposed to a disinfectant. After 10 minutes, 90% of the cells are killed. How many cells remain viable after 20 minutes?
Question:
How many cells remain viable after 20 minutes?

A. 500
B. 100
C. 10
D. 1
E. 0
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Answer / Question:

The answer is C.

For Your Ready Reference :

CELL GRowth:

The Cell Cycle

All dividing cells follow the same basic sequence for replication. The cell generation time is the length of time required to complete the five phases of the cell cycle (Fig. 28-8). The G1 phase (G stands for gap) involves various cellular activities, such as protein synthesis, RNA synthesis, and DNA repair. When prolonged, the cell is considered to be in the G0, or resting, phase. G1 cells may either terminally differentiate into the G0 phase or re-enter the cell cycle after a period of quiescence. During the S phase, new DNA synthesis occurs. The G2 (premitotic) phase is characterized by cells having twice the DNA content as they prepare for division. Finally, actual mitosis and chromosomal division takes place during the M phase.

Tumors do not have faster generation times, but instead have many more cells in the active phases of replication. In contrast, normal tissues have a much larger number of cells in the G0 phase. As a result, cancer cells proceeding through the cell cycle are highly sensitive to chemotherapeutic agents, whereas normal cells in G0 are protected. This growth pattern disparity underlies the effectiveness of chemotherapeutic agents.

Cancer Cell Growth

Tumors are characterized by a gompertzian growth pattern (Fig. 27-1). Fundamentally, a tumor mass requires progressively longer times to double in size as it enlarges. When a cancer is microscopic and nonpalpable, growth is exponential. However, as a tumor enlarges, the number of its cells undergoing replication decreases.

Principles of Chemotherapy


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