Selecting a pathogen from a mixed culture A disease-producing (pathogenic) species present within a mixed culture can often be selected based on which distinguishing property when using suitable laboratory models or host systems?

Introduction / Context:
When a clinical or environmental sample contains a mixture of microbes, the objective is to recover the causative pathogen. Beyond nutritional selection, microbiologists may exploit the organism’s pathogenic properties using in vivo or ex vivo models to enrich or identify the disease-causing species.

Given Data / Assumptions:

• The culture is mixed and includes at least one pathogen.
• Some pathogens exhibit virulence in susceptible hosts (for example, laboratory animals, cell cultures, embryonated eggs).
• Nutritional selection alone may not uniquely identify a pathogen in complex flora.

Concept / Approach:
Selective recovery can be achieved by leveraging virulence. Historically, inoculation into a susceptible host (animal passage) enriches for pathogenic organisms because they multiply in vivo while commensals fail to persist. Modern analogs include invasion assays on cell lines, toxin detection, or bacteriophage susceptibility tests that reflect pathogenic traits. While specialized media (carbon or nitrogen sources) can be helpful, many pathogens share nutritional profiles with commensals, making pathogenic properties more discriminating.

Step-by-Step Solution:
Define the goal: select the disease producer from a mixed population.Identify a discriminant that commensals lack: virulence in a host or model system.Recognize that special carbon/nitrogen requirements are neither necessary nor sufficient in many cases.Choose pathogenic properties as the most reliable basis for selection when appropriate facilities and ethics permit.

Verification / Alternative check:
Classical methods such as Koch’s postulates employed animal inoculation to isolate and re-isolate the pathogen, demonstrating disease causation and effectively selecting the disease-producing agent.

Why Other Options Are Wrong:

• B/C: Nutritional idiosyncrasies occur but are not universal markers of pathogenicity.
• D: Not correct because pathogenic properties can be used.
• E: Pigment can be characteristic (for example, Pseudomonas), but pigments are not general selectors for disease producers.

Common Pitfalls:
Assuming one medium will always select the pathogen. In practice, combined strategies (selective media plus virulence or toxin assays) yield the best results.

Final Answer:
Pathogenic properties (for example, virulence in a susceptible host)