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Transduction and elimination of resistance determinants in methicillin-resistant Staphylococcus aureus
Abstract:
Elimination and transduction of drug resistance was examined in methicillin-resistant strains of Staphylococcus aureus. Irreversible spontaneous loss and "curing" by aging of cultures and by treatment with ethidium bromide indicated that the determinants for penicillinase production and chloramphenicol resistance, and probably also for neomycin resistance, were located extrachromosomally. On the other hand, the determinants of resistance to erythromycin, streptomycin, tetracycline, and methicillin could not be eliminated by acridines, ethidium bromide, rifampin, sodium dodecyl sulfate, ultraviolet (UV) irradiation, growth at 43.5 C, aging of cultures, or combinations of these treatments. The stimulation of transduction frequency by UV irradiation of phage in the case of the stable markers, but not in the case of the unstable ones, supported further the hypothesis of chromosomal location of the markers of methicillin, erythromycin, tetracycline, and streptomycin resistance and extrachromosomal location of the determinants for penicillinase production and chloramphenicol resistance. Neomycin resistance could not be transduced. Joint elimination and co-transduction of the determinants for penicillinase production and resistance to chloramphenicol and neomycin were not observed, indicating the location of these markers on separate, mutually compatible plasmids. Co-transduction of chromosomal resistance determinants was usually less than 1%, which makes the location of these genes in a circumscribed area of the chromosome improbable.
Insights
Drug resistance in Staphylococcus aureus strains was studied. Penicillinase, chloramphenicol, and neomycin resistance were extrachromosomal, while others were chromosomal, impacting treatment strategies.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) poses significant public health challenges due to its resistance to multiple antibiotics.
- Understanding the genetic basis of antibiotic resistance in MRSA is crucial for developing effective treatment strategies.
Purpose of the Study:
- To investigate the location (chromosomal vs. extrachromosomal) of antibiotic resistance determinants in MRSA.
- To differentiate between stable and unstable resistance markers and their implications for genetic manipulation.
Main Methods:
- Treatment of MRSA cultures with various agents (ethidium bromide, acridines, UV irradiation) to induce elimination of resistance markers.
- Transduction experiments using bacteriophage to transfer resistance genes between bacterial strains.
- Analysis of co-transduction frequencies to infer gene linkage and location.
Main Results:
- Penicillinase production, chloramphenicol resistance, and likely neomycin resistance determinants were located extrachromosomally and could be eliminated.
- Resistance to erythromycin, streptomycin, tetracycline, and methicillin was chromosomally located and resistant to elimination treatments.
- UV irradiation stimulated transduction of chromosomal markers but not extrachromosomal ones.
- Neomycin resistance was not transduced, and resistance determinants for penicillinase, chloramphenicol, and neomycin were located on separate plasmids.
Conclusions:
- MRSA exhibits a mixed genetic basis for antibiotic resistance, with some determinants on plasmids and others on the chromosome.
- The distinct locations of resistance genes have implications for the stability and transmissibility of antibiotic resistance in Staphylococcus aureus.
- Separate plasmids likely carry resistance to penicillinase, chloramphenicol, and neomycin, suggesting independent acquisition or maintenance mechanisms.