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

Option (2), To detect penicillin-resistant mutants, the first step is to determine the wild type bacterial susceptibility to penicillin, thus establishing a baseline for identifying resistance in patient isolates.

Step-by-step explanation:

The first step in conducting an experiment to screen for penicillin-resistant mutants in a bacterial species is to determine whether the wild type cells of the same bacterial species are susceptible to penicillin. This is crucial as it establishes a baseline for comparison when testing the isolated bacterial strains from patients. Knowledge of the wild type's sensitivity ensures that any resistance observed is due to the presence of mutants rather than intrinsic resistance of the bacterial species.

To further understand the transfer of penicillin resistance, the experiment could involve a setup in which two cultures of bacteria are separated by a filter that allows the exchange of small molecules but not the bacteria themselves. After incubation, the appearance of resistant cells on the side with the previously penicillin-sensitive cells suggests possible genetic mechanisms at play such as bacterial transformation, transduction, or conjugation.

Finally, the Kirby-Bauer antibiotic susceptibility test is a common method used to determine the susceptibility of bacteria to antibiotics. This involves placing a disk saturated with the antibiotic on a bacterial culture and measuring the zone of inhibition created by the diffusion of the antibiotic in the medium, thereby identifying bacterial susceptibility or resistance.