Phage typing can be done for –
**Core Concept**
Phage typing is a method used to differentiate between bacterial strains based on their susceptibility to specific bacteriophages, which are viruses that infect bacteria. This technique relies on the unique interactions between the bacterial cell surface and the phage, allowing for the identification of specific strains.
**Why the Correct Answer is Right**
Phage typing is particularly useful for differentiating between strains of *Staphylococcus aureus* and *Salmonella typhi*. The process involves infecting the bacterial culture with a specific phage and observing the outcome. If the bacteria are susceptible, the phage will cause lysis and a clear zone will appear on the agar plate. This method is especially useful in epidemiological studies to track the spread of disease. The unique phage susceptibility profiles of different bacterial strains make phage typing a valuable tool for strain identification.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because phage typing is not typically used for *Escherichia coli* strains. While phage typing can be used for some *E. coli* serotypes, it is not a primary method for differentiating between strains.
**Option B:** This option is incorrect because phage typing is not a reliable method for differentiating between *Pseudomonas aeruginosa* strains. Other methods, such as antibiotic susceptibility testing and molecular typing, are more commonly used for this purpose.
**Option C:** This option is incorrect because phage typing is not typically used for *Klebsiella pneumoniae* strains. Other methods, such as molecular typing and antibiotic susceptibility testing, are more commonly used for this purpose.
**Clinical Pearl / High-Yield Fact**
Phage typing is a valuable tool for epidemiological studies, allowing researchers to track the spread of disease and identify the source of outbreaks. This method is particularly useful for differentiating between strains of *Staphylococcus aureus* and *Salmonella typhi*.
**Correct Answer: C. Salmonella typhi**