Bacteriophage entry — What is the first step in infection of a bacterial host cell by a phage?

Introduction / Context:
Phage infection is a multi-step process with defined order: adsorption, penetration, biosynthesis, assembly, and release. Mislabeling the first step confuses receptor biology and host-range concepts.

Given Data / Assumptions:

• We consider tailed bacteriophages as canonical examples.
• Specificity is mediated by tail fibers or other receptor-binding structures.

Concept / Approach:
Adsorption (attachment) to host receptors such as LPS, teichoic acids, or transport proteins is the initiating interaction. Only after stable attachment does the phage inject its nucleic acid (penetration). Replication is later, and “absorption” refers to a physical process unrelated to infection steps.

Step-by-Step Solution:

Verification / Alternative check:
Classical one-step growth experiments and EM studies confirm visible attachment prior to DNA ejection and intracellular replication events.

Why Other Options Are Wrong:

• Absorption: not a virology lifecycle term; distractor.
• Penetration: follows adsorption.
• Replication: occurs after uncoating/penetration.

Common Pitfalls:
Swapping “adsorption” with “absorption”; in virology, adsorption = attachment.

Final Answer:
Adsorption (attachment to specific receptors)