In The X-Bacteria practical protocol, students will investigate the way in which bacteria can acquire antibiotic resistance.
Conjugation is the process in which DNA is transferred between cells through a special
sex pilus or tube. In effect, two strains of bacteria, each resistant to a different antibiotic, are
mated. The mated cells are then tested to find out if conjugation has occurred and antibiotic resistance has been transferred.
In this protocol the recipient strain (E. coli J-53R) carries on its chromosome a gene which confers resistance to the antibiotic rifampicin. The donor strain (E. coli HT-99) harbours a plasmid that includes a gene conferring resistance to a second antibiotic, chloramphenicol. Samples of the two strains of bacteria are mated.
Next, the recipient, donor and mated cells are plated on three different types of media: one containing rifampicin, one containing chloramphenicol and a third containing both antibiotics. After the incubation period, students interpret the results. They should find that antibiotic resistance has been transferred from one strain of E. coli to the other.
What's in the kit?
The X-Bacteria kit contains everything you need to carry out this experiment in school, including:
- slopes of both E. coli strains
- Petri dishes
- teacher notes
- a book – 99% Ape: How Evolution Adds Up, by Jonathan Silvertown
In addition, you'll find taste test strips for another experiment, A Question of Taste. You can try out this experiment with your class, then take part in a UK-wide survey. For more information on A Question of Taste, click here.
How long will it take?
There are three lessons required to carry out this investigation:
- preparation and
- streaking the plates with the cultures
examining and interpreting the results
Are the E. coli strains hazardous?
The strains of bacteria used in the X-Bacteria kit are classed as Hazard Group 1. You should read the following guidelines before handling them.
How do I order?
Whole kits and replacement bacteria and antibiotics can be purchased from here.
Even without a kit you can still carry out Survival Rivals experiments - see the not got a kit page for more information