Drug resistance variation in bacteria - R factor transfer assay

Summary

Some bacteria carry splicing R plasmids and can transmit resistance to sensitive bacteria through splicing, causing them to rapidly turn into drug-resistant bacteria. In addition to horizontal transfer of drug-resistant plasmids in the same species of bacteria, they can also be transferred between different species of bacteria, thus increasing the number of antibiotic-resistant strains and causing great difficulties in prevention and treatment.

Operation method

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Principle

E. coli with streptomycin R factor was used as the donor bacterium and E. dysenteriae sensitive to streptomycin was used as the recipient bacterium. After co-incubation, the streptomycin R factor of the donor bacterium is transferred to the recipient bacterium due to the joining of the donor bacterium and the recipient bacterium, and E. dysenteriae acquires streptomycin resistance, and thus grows on streptomycin-containing S-S plates. The colorless, translucent colonies of E. dysenteriae are colorless because they do not break down lactose. E. coli can break down lactose to produce acid, which makes the indicator (neutral red) colorful on the S-S plate, so it is a pink opaque colony.

Move

1. Inoculate streptomycin-resistant E. coli with streptomycin-sensitive E. coli and Fusarium dysenteriae in broth medium and incubate at 37 ℃ for 10-12 hours.

2. mix streptomycin-resistant E.coli and streptomycin-sensitive E.coli and Fusarium dysenteriae broth cultures in a sterile test tube according to l:4, and incubate at 37 ℃ for 1 hour.

3. Use inoculation ring to dip the above mixture and inoculate on the S-S (or China Orchid) plate containing 100 ug/ml streptomycin (for the preparation of S-S and China Orchid plate, please refer to Experiment IX Enterobacteriaceae), and incubate at 37 ℃ for 18～24 hours.

4. Take streptomycin-sensitive Escherichia coli and Fusarium dysenteriae and mix them according to the above method. 37 ℃ for 1 hour, inoculate S-S plate and S-S plate containing streptomycin, and incubate at 37 ℃ for 18～24 hours.

5. Observe the growth of the above bacteria on S-S (or Chinese orchid) plates and S-S plates containing streptomycin.

Caveat

What is meant by drug resistance variants? What is the practical significance of understanding drug resistance variants?

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