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Plasmid-mediated resistance to aminocyclitol antibiotics in group D streptococci
Abstract:
Streptococcus faecalis BM4100 was resistant to high levels of gentamicin, kanamycin, and structurally related antibiotics. The genes conferring resistance to aminocyclitols in this strain were carried by a plasmid, pIP800, self-transferable to other S. faecalis strains. The aminocyclitol resistance was mediated by constitutively synthesized phosphotransferase and acetyltransferase activities. It was inferred that phosphorylation occurred at the 2"-hydroxyl group and that acetylation occurred at the 6'-hydroxyl group of the aminocyclitols. The enzyme activities were not separable by gel filtration or by isoelectric focusing. Their apparent molecular weight was 31,000, and their isoelectric point was 5.3. With respect to substrate profile, size, and charge, the transferases from strain BM4100 resembled closely those with identical site specificity described in staphylococci. These results suggest that plasmid gene transfer may occur between the two pathogenic bacterial genera.
Insights
Streptococcus faecalis BM4100 exhibits high-level resistance to aminocyclitol antibiotics due to plasmid-borne genes. These genes encode enzymes that modify antibiotics, suggesting potential gene transfer between bacterial genera.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Streptococcus faecalis BM4100 displays resistance to gentamicin, kanamycin, and related antibiotics.
- This resistance is conferred by genes located on a self-transferable plasmid, pIP800.
Purpose of the Study:
- To investigate the genetic and enzymatic basis of aminocyclitol resistance in Streptococcus faecalis BM4100.
- To characterize the enzymes responsible for antibiotic resistance and their potential origin.
Main Methods:
- Plasmid analysis to identify resistance genes.
- Enzyme characterization including gel filtration and isoelectric focusing.
- Substrate specificity analysis of the identified enzymes.
Main Results:
- The plasmid pIP800 carries genes mediating aminocyclitol resistance.
- Resistance is due to constitutively synthesized phosphotransferase and acetyltransferase activities.
- Enzymes have an apparent molecular weight of 31,000 and an isoelectric point of 5.3.
- Enzymes modify specific hydroxyl groups on aminocyclitol antibiotics.
Conclusions:
- Plasmid-mediated gene transfer of antibiotic resistance mechanisms is evident in Streptococcus faecalis.
- The characterized resistance enzymes show similarities to those found in staphylococci.
- These findings suggest the possibility of horizontal gene transfer between Streptococcus and Staphylococcus genera.