Question

A public health microbiologist plans to screen a particular bacterial species that was isolated from several patients in an intensive care unit to detect if any of the cells are penicillin-resistant mutants. What is the first step in conducting this experiment?

1) Determine whether or not wild type cells of the same bacterial species are susceptible to penicillin.
2) Test the cells to see if they can grow on media to which penicillin has been added.
3) Perform an antibiotic susceptibility test on the cells using antibiotics other than penicillin that are known to be effective.
4) Set up an Ames test to see if any of the isolates are mutagenic.

Answer 1

The first step in screening for penicillin-resistant bacterial mutants is to confirm the susceptibility of the wild type cells to penicillin. This acts as a control and ensures the experiment's validity before performing an antibiotic susceptibility test, such as the Kirby-Bauer assay.

Step-by-step explanation:

The first step in conducting an experiment to screen a particular bacterial species for penicillin-resistant mutants would be to determine whether the wild type cells of the same bacterial species are susceptible to penicillin. This is a crucial control to establish a baseline of sensitivity before testing the isolated bacterial strains.

If the wild type is not susceptible to penicillin, the subsequent experiments would not be informative. However, if the wild types are susceptible, any detected resistance in the isolates could suggest the presence of penicillin-resistant mutants.

The antibiotic susceptibility test, such as the Kirby-Bauer disk diffusion assay, would then be performed to assess the susceptibility of the bacterial cells. The presence of a penicillinase enzyme, which some bacterial strains produce to break down penicillin, is a common mechanism of resistance.