Multiple Choice
Why is it necessary to dilute a sample when determining bacterial numbers using plate counts?
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1. Introduction to Microbiology
Introduction to Microbiology
Multiple Choice
Which of the following would NOT be a likely member of the normal microbiota of the skin surface?
A
Escherichia coli
B
Propionibacterium acnes
C
Staphylococcus epidermidis
D
Micrococcus luteus
Verified step by step guidance1
Understand the concept of normal microbiota: These are microorganisms that typically reside on or within a healthy human body without causing disease, often providing beneficial effects or simply coexisting harmlessly.
Recall the typical environment of the skin surface: The skin is generally dry, acidic, and exposed to oxygen, favoring certain bacteria adapted to these conditions.
Identify common skin microbiota: Bacteria such as Propionibacterium acnes (now Cutibacterium acnes), Staphylococcus epidermidis, and Micrococcus luteus are well-known residents of the skin because they thrive in this environment.
Consider the characteristics of Escherichia coli: E. coli is primarily found in the intestinal tract, which is a moist, nutrient-rich, anaerobic environment, making it unlikely to be a normal resident of the dry, aerobic skin surface.
Conclude that Escherichia coli would NOT be a likely member of the normal skin microbiota based on its typical habitat and environmental preferences.
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