Lab Report 14: Bacteriophage Specificity

Answers

1. Purpose of the exercise

The purpose is to test bacteriophage host specificity: whether the phage suspension can productively infect each bacterial host tested in the exercise. Visible lysis or plaque formation on a bacterial lawn indicates which hosts support productive infection under the conditions tested.

2. Observation table

The printed report sheet provides three blank rows and does not identify the bacteria or supply any lysis results. Complete the table with the organisms and observations from the actual exercise:

3. Evidence that the bacteriophage infected the bacteria

A plaque is a localized area of visible clearing in an otherwise continuous bacterial lawn. It develops when bacteriophages productively infect susceptible cells, replicate, lyse those cells, and spread to nearby cells. Plaques therefore support this interpretation:

$$\text{plaque} \Longrightarrow \text{productive infection detected}$$

4. Why the bacteriophage may not infect all three bacteria

Bacteriophages do not infect bacteria indiscriminately. Receptor-binding proteins on a phage must recognize compatible, accessible receptors on the bacterial surface. After attachment, the host must also permit genome entry and phage replication; bacterial defenses or other intracellular incompatibilities can prevent a productive infection.

Use the completed observation table to identify which tested hosts showed lysis. A “no” result means productive infection was not detected for that host under the conditions of this exercise; it does not mean that the species can never be infected by any bacteriophage.

5. Explanation for bacteriophage specificity

Bacteriophage specificity begins with compatible recognition between phage attachment proteins and receptors on the bacterial surface. Productive infection also depends on successful genome entry, replication, assembly, and release inside the host. A mismatch or defense at any of these stages can prevent plaque formation.

Conclusion

The exercise demonstrates bacteriophage host specificity. Record the actual organisms and lysis observations from the experiment, then explain the pattern using receptor compatibility and the intracellular requirements for productive infection.