A researcher identifies a gene in Streptococcus pyogenes that is suspected to encode a toxin. The gene is present in strains that cause disease but absent in closely related non-pathogenic strains. The researcher deletes the gene from the bacterial genome and finds that the mutant strain no longer causes disease in mice.

Which of Falkow’s molecular postulates has the researcher fulfilled? (select all that apply)

Which of the following is a known limitation of Koch’s postulates?

Which of the following individuals could be considered asymptomatic carriers of an infectious disease? (select all that apply)

Which of the following traits would help a pathogen antagonise host defences? (select all that apply)

A researcher is studying two strains of the same bacterial species (A & B). Strain A causes a mild respiratory illness that typically resolves without treatment. Strain B causes a severe respiratory disease requiring hospitalisation. Select the correct statement:

A research team collects stool samples from a healthy adult volunteer to study microbial diversity in the human gut. The volunteer provides three samples over the course of a single day: one in the morning, one in the afternoon, and one in the evening. The research team compares the microbial composition of the three samples.

What is this research project investigating?

I am a gram positive rod-shaped bacterium and a strict anaerobe. I am part of the normal human microbiota and have a commensal relationship with human hosts.

In which of the following body sites is this bacterium most likely to reside?

In which region of the respiratory tract would you find the largest density of normal microbiota?

Which of the following sites in the human body are considered sterile under normal conditions? (select all that apply)

The most common symbiotic relationships between a human host and its normal microbiota are: (select all that apply)