Use the following choices to answer questions 7–10:
a. Campylobacter
b. Cryptosporidium
c. Escherichia
d. Salmonella
e. Trichinella


Microscopic observation of a stool sample reveals gram-negative helical cells.

Verified step by step guidance

1. Identify the characteristics of the organism observed in the stool sample: gram-negative and helical cells.
2. Review the list of choices provided: Campylobacter, Cryptosporidium, Escherichia, Salmonella, and Trichinella.
3. Recall that Campylobacter is known for being a gram-negative, helical-shaped bacterium.
4. Consider the other options: Cryptosporidium is a protozoan, Escherichia (such as E. coli) is a rod-shaped bacterium, Salmonella is also rod-shaped, and Trichinella is a parasitic worm.
5. Conclude that the organism observed in the stool sample is most likely Campylobacter based on its gram-negative, helical shape.

Key Concepts

Gram-Negative Bacteria

Gram-negative bacteria are characterized by their cell wall structure, which includes a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides. This structure makes them more resistant to certain antibiotics and is crucial for their identification in microbiological studies. The Gram staining technique reveals these bacteria as pink under a microscope, indicating their unique cell wall composition.

Helical Cell Morphology

Helical cell morphology refers to the spiral shape of certain bacteria, which can influence their motility and pathogenicity. This shape is often associated with specific genera, such as Campylobacter and Helicobacter. Understanding the morphology helps in the identification of bacteria during microscopic examination, as it provides clues about their classification and potential health implications.

Stool Sample Analysis

Stool sample analysis is a critical diagnostic tool in microbiology for detecting gastrointestinal pathogens. It involves examining the sample for the presence of bacteria, parasites, or viruses that can cause infections. Microscopic observation, as mentioned in the question, allows for the identification of specific organisms based on their morphology, aiding in the diagnosis of conditions like gastroenteritis.