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Ch. 1 - The Microbial World and You
Chapter 1, Problem 25.5a

Microscopic examination of a patient’s fecal culture shows comma-shaped bacteria. These bacteria require 2-4% NaCl to grow. The bacteria probably belong to the genus
a. Campylobacter.
b. Escherichia.
c. Salmonella.
d. Shigella.
e. Vibrio.

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1
Identify the shape of the bacteria: The problem states that the bacteria are 'comma-shaped'.
Recall the characteristics of the genera listed: Campylobacter, Escherichia, Salmonella, Shigella, and Vibrio.
Note that Vibrio species are known for their distinctive comma shape.
Consider the growth requirements: The bacteria require 2-4% NaCl to grow.
Recognize that Vibrio species, such as Vibrio cholerae, are halophilic, meaning they thrive in environments with higher salt concentrations, matching the growth requirement.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Vibrio genus characteristics

The Vibrio genus includes comma-shaped, gram-negative bacteria that are often found in aquatic environments. They are known for their requirement of a saline environment, typically thriving in conditions with 2-4% NaCl. This characteristic is crucial for their growth and differentiation from other genera, making them significant in clinical microbiology, especially in cases of gastroenteritis.
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Fecal culture analysis

Fecal culture analysis is a laboratory technique used to isolate and identify pathogens present in a patient's stool sample. This method helps in diagnosing gastrointestinal infections by allowing the growth of specific bacteria under controlled conditions. The morphology and growth requirements of the bacteria, such as shape and salt tolerance, are key indicators for identifying the causative agent.
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Differentiation of enteric bacteria

Differentiating enteric bacteria involves understanding the unique biochemical and morphological traits of various bacterial genera that inhabit the gastrointestinal tract. This includes recognizing specific growth requirements, such as salt concentration, and identifying characteristic shapes and metabolic processes. Such differentiation is essential for accurate diagnosis and treatment of infections caused by these bacteria.
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