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Characterization of a novel bacteriocin-encoding plasmid found in clinical isolates of Staphylococcus aureus
M R Gamon1, E C Moreira, S S de Oliveira
1Departamento de Microbiologia Geral, Instituto de Microbiologia, Universidade Federal do Rio de Janeiro, Brazil.
Abstract:
Plasmids specifying bacteriocin production and immunity to its action were found in three clinical isolates of Staphylococcus aureus obtained in different hospitals located in Rio de Janeiro. These plasmids (pRJ28, pRJ29 and pRJ30) of 8.0 kb were found to generate identical restriction fragment patterns upon digestion with several enzymes, although the range of strains susceptible to the respective bacteriocin varied among the producer strains, when different Gram-positive bacteria were used as indicators, pRJ29 was then chosen for further characterization in order to compare it with pRJ6 and pRJ9, two small bacteriocin-encoding plasmids previously described in strains isolated from food. pRJ29 was found to code for a bacteriocin with chemical properties (sensitivity to proteases, heat resistance, activity under anaerobiosis, and estimated molecular weight) similar to those of pRJ6-encoded bacteriocin, conferring cross-immunity to it. However, its restriction map differed from those of pRJ6 and pRJ9. These studies together with hybridization, incompatibility, and mobilization analyses using a derivative of pRJ29 tagged with Tn917-lac suggest that pRJ29 is a mosaic composed of genetic determinants found on pRJ6 and pRJ9, and that IS257 was not involved in the recombination events which gave rise to pRJ29.
Insights
Three Staphylococcus aureus plasmids from Rio de Janeiro clinical isolates produce bacteriocins. These plasmids share identical restriction patterns but vary in bacteriocin activity, suggesting a mosaic genetic structure.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Bacteriocin production in Staphylococcus aureus is often plasmid-mediated.
- Understanding bacteriocin-encoding plasmids is crucial for antimicrobial resistance research.
Purpose of the Study:
- To characterize bacteriocin-encoding plasmids from clinical Staphylococcus aureus isolates.
- To compare these plasmids with previously described food-borne isolates.
Main Methods:
- Plasmid isolation and characterization using restriction enzyme digestion.
- Bacteriocin activity assays with Gram-positive indicator strains.
- Hybridization, incompatibility, and mobilization analyses.
Main Results:
- Identical 8.0 kb plasmids (pRJ28, pRJ29, pRJ30) were identified in clinical isolates.
- Bacteriocin activity varied among producer strains.
- pRJ29 exhibited similar bacteriocin properties and cross-immunity to pRJ6 but had a different restriction map, suggesting a mosaic structure derived from pRJ6 and pRJ9.
Conclusions:
- Clinical Staphylococcus aureus plasmids can possess mosaic genetic structures.
- The mosaic nature of pRJ29 may arise from recombination of genetic elements from different plasmids.
- IS257 insertion sequences were not implicated in the formation of pRJ29.