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'DNA' as contaminants in antibiotics and its capacity to transform bacteria to drug resistance
A N Chakrabarty1, S G Dastidar, M Ganguli
1Department of Medical Microbiology and Parasitology, University College of Medicine, Calcutta University, India.
Abstract:
DNA/and deoxyribose sugars were detected in streptomycin (Sm), kanamycin, polymyxin, penicillin G, ampicillin, methicillin, cloxacillin and mitomycin C in small amounts/traces. Stained DNA could be feebly visualized directly in Sm run in agarose gel, which improved after its separation and concentration. These DNA materials were DNase sensitive, RNase and pronase resistant, and appeared to consist of fragments, c. less than or equal to 6 Mdal; this could repeatedly transform to SmR several recipient enterobacteria and vibrios; E. coli C600 and S. typhi 57, after such transformation revealed similar plasmid DNA bands that were absent in their wild-types. G + C mole% of plasmid and chromosomal DNA of recipient (57) along with that of Streptomyces griseus reference strain, suggested an extraneous origin for the plasmid DNA.
Insights
Antibiotics like streptomycin contain trace DNA that can transform bacteria. This extrachromosomal DNA, identified as plasmid DNA, was successfully transferred to recipient bacteria, altering their genetic makeup.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Antibiotics are known to have antimicrobial effects, but their potential to carry genetic material is less understood.
- Trace amounts of DNA and deoxyribose sugars were detected in several common antibiotics.
- The presence of DNA in antibiotics raises questions about potential horizontal gene transfer.
Purpose of the Study:
- To investigate the nature and functional capacity of DNA detected in antibiotics.
- To determine if antibiotic-associated DNA can be transferred to and expressed by bacteria.
- To characterize the origin of the transferred DNA.
Main Methods:
- Detection and visualization of DNA in antibiotic samples using agarose gel electrophoresis.
- Sensitivity assays using DNase, RNase, and pronase enzymes.
- Transformation experiments using enterobacteria and vibrios as recipient cells.
- Plasmid DNA analysis via gel electrophoresis and G+C content determination.
Main Results:
- DNA was detected in trace amounts in antibiotics including streptomycin, kanamycin, and penicillin G.
- The DNA was sensitive to DNase but resistant to RNase and pronase, indicating a DNA nature.
- The DNA fragments, approximately ≤6 Mdal, were capable of transforming recipient bacteria (Enterobacteria, Vibrios, E. coli C600, S. typhi 57) to streptomycin resistance (SmR).
- Transformed bacteria exhibited new plasmid DNA bands not present in wild-type strains.
- G+C content analysis suggested an extraneous origin for the plasmid DNA.
Conclusions:
- Antibiotics can contain functional DNA fragments capable of horizontal gene transfer.
- This DNA appears to be plasmid DNA of extrachromosomal origin.
- The findings highlight a potential mechanism for antibiotic resistance spread and genetic exchange in bacteria.